April 2008

Shellfish Industry Development Strategy A Case for Considering MSC Certification for Shellfish Cultivation Operations

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CONTENTS

Page

Executive Summary 3

Introduction 5

Mollusc Cultivation Mussel Cultivation Bottom Culture 6

Spat Collection 6 Harvesting 7

Suspended Culture 7 Longline Culture 8 Pole Culture 8 Raft Culture 9 Spat Collection 10 Environmental Impacts 11

Scallop Cultivation Japanese Method 13 New Zealand Methods 15 Scottish Methods 15 Environmental Impacts 16

Abalone Cultivation 16 Hatchery Production 17 Sea Culture 17 Diet 18 Environmental Impacts 19

Clam Cultivation 19 Seed Procurement 20 Manila Clams 20 Blood Cockles 20 Razor Clams 21 Siting of Grow Out Plots 21 Environmental Impacts 21

Oyster Cultivation 23 Flat Oysters 24 Cupped Oysters 24 Hanging Culture 24 Raft Culture 24 Longline Culture 25 Rock Culture 25 Stake Culture 25 Trestle Culture 25 Stick Culture 26

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Ground Culture 26 Environmental Impacts 27

Crustacean Culture Clawed Lobsters

Broodstock 29 Spawning 29 Hatching 29 Larval Culture 30 Nursery Culture 30 On-Growing 31 Ranching 31 Environmental Impacts 32

Spiny Lobsters 32 Broodstock and Spawning 33 Larval Culture 33 On-Growing 33 Environmental Impacts 34

Crab Cultivation Broodstock and Larvae 34 Nursery Culture 35 On-growing 35 Soft Shell Crab Production 36 Environmental Impacts 36

Conclusions 37

Acknowledgements 40

References 40

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EXECUTIVE SUMMARY

The current trend within the seafood industry is a focus on traceability and sustainability with consumers and retailers becoming more concerned about the over-exploitation of our oceans. The Marine Stewardship Council (MSC) has a sustainability certification scheme for wild capture fisheries. Currently there is no certification scheme for products from enhanced fisheries1 and aquaculture2. It is the view of many producers that the production of shellfish in enhanced fisheries and aquaculture is more sustainable than the wild capture fisheries for these products and that certification for these products should be considered. The purpose of this report was to review the current scientific literature and compare the results to the criteria required for compliance to Principle 2 of the MSC s Principles and Criteria for Sustainable Fishing in order to determine whether such enhanced shellfisheries could proceed through MSC assessment.

Shellfish production can be divided into mollusc cultivation and crustacean cultivation. Mollusc cultivation mainly concerns bivalve molluscs such as mussels, oysters and scallops. For example mussel culture takes place on the seabed or in suspension from rafts and longlines. Bottom culture is characterised by the re-laying of wild harvested spat onto subtidal and intertidal beds. The mussels are grown for 1-2½ years before harvesting by either hand-collection, hand-raking or hydraulic dredge. Hand-collection and hand-raking support artisanal fisheries and have little impact on the environment, and as such may comply with the criteria for Principle 2. The use of hydraulic dredges has a greater impact on the environment which may prove too detrimental to allow compliance to Principle 2. For a definitive conclusion to be made research into this specific area should be conducted. The main issue with suspended culture concerns the increase in sedimentation below farm systems and the effect sedimentation has on the ecosystem. In the context of this report, sedimentation refers to the settlement of organic and inorganic particulate matter settling from the water onto the seabed. There are conflicting arguments within the literature; however the majority of research indicates that impacts are minimal and localised. It is possible to show that suspended culture could comply with Principle 2.

Scallop cultivation is similar to mussel culture in that it can be divided into suspended culture or bottom culture, although bottom culture is classified as stock enhancement due to the mobile nature of scallops. Suspended culture has the same potential impacts of mussel culture with sedimentation being the primary concern. There has been much less research into the cultivation of scallops but the current research suggests that there are no adverse impacts on the environment. The restocking of scallops has a more detrimental impact on the environment due to the harvesting method by dry dredge (scallop dredge), which is a high-impact gear which could be destructive if used in sensitive areas.

The environmental impacts of abalone culture have received little if any attention from the scientific community and as such no conclusion regarding compliance to Principle 2 could be made. It is noted that there may be issues with the use of wild harvested algae as a food source for the abalone.

Clam culture generally takes place in or on the seabed. As with other bottom cultures, the use of dredging to harvest the product could raise concerns regarding the environmental impacts of this activity if used in sensitive areas. More research is required in this area as the conclusions often have to be inferred from wild capture fisheries which impact much larger

1 An enhanced fishery is described as a wild capture fishery where the natural population is enhanced through the input of hatchery reared juveniles or the introduction of structures to enhance production. 2 Aquaculture can be defined in many ways; for the purpose of this report aquaculture is defined as the controlled farming of aquatic organisms from the larval stage to commercial size.

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areas. There are also examples of clams being grown in bags placed on trestles. This method has a reduced impact and may comply with the criteria for Principle 2.

Oyster cultivation is possibly one of the most sustainable types of shellfish culture. There are a wide range of methods for culturing oysters, mainly concerned with the use of a structure to support the growth of the oysters either in suspended culture or on the seabed. Concerns have been raised regarding the removal of large quantities of phytoplankton (Chapelle et al, 2000; Newell, 2004) and the increase in sedimentation, however, as with mussel culture there are conflicting arguments within the literature and it appears that local conditions have an important influence on the extent of impacts from culture systems. The major concern with oyster culture in the USA is the use of Carbaryl, a pesticide, to control burrowing shrimp populations. By removing organisms from the ecosystem such a practice could result in a failure to meet the criteria of Principle 2.

In contrast to mollusc culture, the culture of crabs and lobsters is in its infancy. Lobster culture is mainly concerned with taking wild broodstock and rearing larvae to a stage where survival rates are higher than in the wild, at which point the juvenile lobsters are re-introduced into the natural environment. The use of local broodstock and selective harvesting methods of the fishery could meet the criteria for Principle 2. Providing the natural population is not over exploited and healthy, the restocking exercises can improve the wild stocks. Spiny lobsters have received more attention in the tropics and the concerns with their culture are the low numbers of available larvae from wild stocks.

Crab culture is confined to the tropics where the current trend is to integrate the culture with mangrove regeneration. Integrated cultivation methods of this kind are improving the environment and could provide a good example to the rest of the aquaculture industry. The concerns over crab culture are the use of wild caught larvae for on-growing and the use of by-catch as a food source. At present the industry is perceived as small and sustainable and would likely meet the criteria for Principle 2, but to support a growth of the industry hatchery production of larvae and artificial feeds will need to be developed.

In conclusion, it appears that local conditions are vitally important as to whether the impacts from shellfish aquaculture are having a detrimental effect. A principle that should be considered when assessing the sustainability of a product is the carrying capacity of the culture site. In particular interest of environmental sustainability is the ecological carrying capacity, which is the level of production that an area can support without having a negative impact on the environment. The carrying capacity can be assessed using models and it is suggested that these models are used for each site when considering whether a product is sustainable. It should also be noted that shellfish culture can have positive effects on the environment by filtering the water column and removing excess nutrients and increasing benthic-pelagic coupling (Newell, 1988; Mann, 2000) and that this should be considered, and written into the criteria for principles of sustainability, as it is an important factor that wild capture fisheries cannot offer.

Enhanced shellfisheries should be considered as suitable for proceeding through MSC assessment as though a wild-caught fishery as they operate quite differently from traditional finfish aquaculture systems.

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INTRODUCTION

The shellfish industry relies on a complex relationship between producer, retailer and consumer. At present there is a lot of focus from the consumer on traceability, with sustainability of the product being a focal point of this traceability. The demand from the consumer for sustainable produce has led to retailers to search for such products. Sustainable accreditation is currently administered by the Marine Stewardship Council (MSC), who determines whether a fishery is managed effectively and fished in a sustainable manner. Currently, the MSC only certifies un-enhanced wild capture fisheries, but with more focus being placed on certified products, there is a call for certification of enhanced fisheries and aquaculture products from some of the larger retailers (http://www.msc.org/html/ni_346.htm). The purpose of this report is to examine the methods used to culture shellfish, or enhance their fisheries, and by reviewing the current scientific research illustrate; any environmental impacts which may prevent the sustainability of the activity, the gaps in the research, and whether there is scope for these products to be certified by the MSC.

The MSC have proposed that enhanced fisheries could be considered for certification if they can be categorised under one of the following production systems:

Type 1. Production systems that involve wild harvest followed by a grow out phase.

Type 2. Production systems that involve the introduction of fish either as eggs, larvae or juveniles. The introductions may be of native species (restocking) or exotic species.

Type 3. Production systems that involve the modification of habitats to make production easier or to favour desirable species.

The methods of cultivation will be categorised as one of the above production systems where possible and if not, additional categories will be proposed. In addition to categorising the production systems, the environmental impacts will also be assessed according to the MSC Principles and Criteria for Sustainable Fishing . In order to be considered sustainable, the impacts from a culture system must be covered by Principle 2 of the document which states;

Fishing operations should allow for the maintenance of the structure, productivity, function and diversity of the ecosystem (including habitat and associated dependant and ecologically related species) on which the fishery depends.

The environmental impacts will be assessed according to the criteria of Principle 2 and a judgement will be made as to whether they would likely pass, fail, or whether there is insufficient research in the area to make a definitive decision.

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MOLLUSC CULTIVATION

MUSSEL CULTIVATION

Mussel production extends to all regions of the globe. The majority of culture takes place in temperate climates and in particular Europe (467 658t in 2005) with Spain, the Netherlands, Denmark and Italy the leading producers, along with China (772 173t in 2005) (FAO, 2007). The primary species for production are the blue mussel, Mytilus edulis, and the Mediterranean mussel, Mytilus galloprovincialis, with green mussels, Perna spp., becoming increasingly important in tropical and sub-tropical climes such as New Zealand and the Far East. The cultivation of mussels can be categorised into two main forms; the two-dimensional bottom culture, or three-dimensional suspended culture, and for the purpose of this report each method will be assessed separately.

Bottom Cultivation

The cultivation of mussels on the seabed occurs in intertidal and subtidal areas in sheltered bays where there is typically an abundant natural spatfall. The main European centre for bottom cultured mussels is the Wadden Sea off the Netherlands, Germany and Denmark. The Dutch have leased large plots of the western area of the Wadden Sea to mussel producers. In the UK areas such as The Wash and Morcambe Bay have traditionally supported large mussel fisheries and production; however in recent years there has been a regular failure in mussel recruitment, leading to negligible production. Other areas however have seen increases in production. One such area is the Menai Strait in North Wales. The mussel production in the Menai Strait relies on collected spat from the Irish Sea, which is re-laid in plots around low water springs, where production of the mussels can be maximised. With the use of anti-crab fencing around these plots the farmers in the Menai Strait have obtained yields as high as 8:1 (Spencer, 2002). The bottom culture of mussels can be classified under the type 1 production system described previously (a wild harvest followed by grow out). Below the different stages are discussed with regard to methodology, environmental impacts, and how these effects can be classified.

Spat Collection

Spat are collected at an age of approximately 1 year old, when they measure between 10-30mm shell length (SL) (Spencer, 2002). Spat are generally collected locally from less suitable grounds and re-laid in higher densities in more productive areas. Such a method of local collection results in a minimal impact, if any, on the local genome. There has been little research regarding the collection of mussel seed by dredging, and this is likely to be the process which has the greatest effect on the ecosystem. There has been significant research into the effects of the heavy-duty dredges used to collect scallops in commercial quantities, with evidence showing dramatic decreases in numbers of species and abundance, with recovery periods in excess of 3 months (Thrush et al, 1995; Curry & Parry, 1996; Jennings et al, 2001). The differences between such dredging activities and the collection of mussel spat are numerous, and it is likely that such extreme effects will not be encountered. Firstly the mussel spat tend to be concentrated in high numbers in distinct areas, unlike the sparsely

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aggregated scallops and clams, leading to a reduction in the area affected by dredging. In the UK, licenses to collect mussel spat are issued only following the formation of mussel mud , which consists of dead shells, silt and pseudofaeces. The mussel mud

creates an unstable layer beneath the spat, which causes the spat to detach their byssal threads. At this stage the dredges are able to skim off the mussel mud, collecting the spat whilst leaving the substratum relatively undisturbed. In terms of reducing natural stocks of mussels by removing the spat, it should be noted that the unstable beds are likely to be destroyed by winter storms, resulting in the loss of the mussels from the fishery (Kaiser et al, 1998). The impacts of mechanical dredging on the environment are likely to be minimal and limited to small areas. The seasonal nature of spat collection also allows recovery periods of up to a year, which should be ample time for the recovery of the ecosystem. One potential impact on the ecosystem from the heavy exploitation of natural mussel beds is the removal of a valuable food source for predators. In 1991 and 1992 the entire intertidal mussel stock was removed from the Wadden Sea, leading to high levels of mortality in the eider duck population which utilised the mussel beds as a major food source. It has been suggested that these effects could persist for many years if beds are not allowed to redevelop and mature (Dankers & Zuidema, 1995). It is the opinion of the author, and others (Kaiser et al., 1998), that providing that entire stocks are not removed, the limited negative effects will be outweighed by the positive benefits. Although there has been little research into the effects of dredging for spat, and as such whether Principle 2 is met or not is inconclusive, attention should be paid to the removal of high proportions of spat. The problems encountered in the Wadden Sea illustrate a possible failure to meet the first criteria of Principle 2 as the functional relationship between mussel and eider duck is altered, resulting in high mortalities of the predator.

Harvesting

Harvesting bottom cultured mussels can vary from mechanised dredging and power dredging as used in the Dutch Wadden Sea and in Poole harbour, England, to simple hand-collection or hand-raking on lower yield operations (Spencer, 2002). As with the collection of spat there is no research into the environmental impacts of mussel collection using dredges. The dredges differ to those used in commercial capture fisheries and as such analogies should not be made. The gap in the research prevents a conclusion being made as to whether harvesting by dredging would comply with Principle 2. That said, it should be noted that the high densities of mussel result in a relatively small area being affected, and the plots are usually re-used soon after harvest and as such the ecosystem could be classified as a permanent commercial mussel bed. Hand-collection and hand-raking, although there is no scientific research supporting this view, are likely to have minimal environmental impact. Hand-collection may involve some trampling of benthos, but recovery rates are likely to be rapid. It is likely that the latter two methods of harvesting could comply with Principle 2 of the MSC criteria, providing the scientific research is performed to prove this.

Suspended Cultivation

The methods of suspended culture utilised in different regions originate from a combination of traditional methods, local availability of materials and site. The advantages of suspended culture methods are the increased exposure to water currents

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and the reduction of predation on the cultured population from benthic predators. There are three principle methods of off-bottom culture; longline, pole, and raft culture, and a variety of different designs and methods have arisen to take advantage of local conditions. All three types of suspended culture are classified as type 1 production systems.

Figure 1: A mussel longline in the River Fal, Cornwall, UK. Two longlines approximately 200m long are supported by a series of buoys.

Longline Cultivation

Longline culture of mussels is the method of choice in more exposed waters due to the flexibility of the structures. A typical arrangement will consist of a series of horizontal ropes that are held in the top 3m of the water column by buoys (Figure 1). From the headlines are a series of dropper ropes, which carry the mussels. The dropper ropes are typically 4-6m in length and spaced at 50cm intervals (Spencer, 2002). The carrying capacity of the longlines is dependant on the volumetric capacity of the floats, and as the mussels grow, additional floats are required to support the crop.

Pole Cultivation

The origins of pole culture lie in France, where it began as early as the thirteenth century, making this method the oldest of the mussel cultivation techniques. Known as the bouchot method, it consists of vertical poles driven into the seabed and is essentially a shallow water technique, with access to the poles at low tide or by diving. The poles are typically 4-7m long (with 2-3m rising above the seabed) and 25-30cm in diameter, and are made from hardwoods such as oak and pine, or more recently aluminium. The poles are places in parallel rows at right angles to the shore line, and are usually positioned around the ELWM3. For this method the spat are collected on poles or coir rope attached to metal frames placed in deeper water. The seed are then transferred to tubular nets, which are then wound around the bouchot

3 Extreme Low Water Mark, the lowest point the tide reaches on spring tides.

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poles and nailed into place. From these nets the seed will migrate out onto the surface of the poles and settle. Tropical culture methods based on the bouchot method include the use of bamboo poles placed in the seabed, and although the materials differ the methods are very similar.

Figure 2: A mussel farm on the River Fal, Cornwall, UK. Visible are the rafts (20m x 12m) and the dropper ropes which extend 8m below the rafts.

Raft Cultivation

The use of rafts to cultivate mussels is becoming increasingly popular and is utilised by many countries including Australia, Chile, USA, Ireland, Scotland, Singapore and Venezuela to name a few. Raft culture is based around a framework of timber supported by floats, with a series of ropes attached within the framework of the raft. The rafts require a water depth several metres deeper than the length of the ropes to prevent the grounding of the mussels during low tides, which would lead to damaging of the mussels and increased predation. Water quality, current speed and shelter are also important in the siting of mussel rafts. On the west coast of Scotland the Muckairn raft is extensively used. Wooden beams 11m in length (10 x 8cm), spaced 50cm apart, are supported by plastic foam-filled floats (120 x 80 x 65cm). Two hundred synthetic ropes, each 8m in length are spaced 25-40cm along the beams (Spencer, 2002). These rafts have a carrying capacity of over 10t each, equating to 6kg of mussel per metre of rope. In the River Fal, Cornwall, a Spanish raft design is used. Timber rafts are 20m long and 12m wide and support 600 dropper ropes, each 8m in length (Figure 2). There are ten rafts in total which results in a culture system 48km in length, producing 200-300 tonnes of mussels a year (S. Kestin, pers. comm.). The farm is situated in 12-14m of water, with depths in the estuary reaching 30m in the main channel. There is considerable current flow through the farm, yet it is still regarded as sheltered as there is little wind or wave action. Salinities are stable at 34ppt as freshwater influence does not reach the farm site. Spat collection occurs at the farm on ropes attached to the raft. The seed are then stripped from the ropes and placed into cotton socking which is then reattached to the ropes (Figure 3), which are

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then replaced onto the rafts. Thinning of the mussels occurs throughout the grow out process.

Figure 3: A hopper being used to fill cotton socking with mussel seed and attaching them to grow out ropes on a raft culture site, River Fal, Cornwall, UK.

Spat Collection

The continuity of suspended mussel cultivation is greatly dependant on the acquisition of spat. Currently the majority of spat is obtained from natural populations. Hatchery produced spat are available; however, for the majority of markets the use of these spat is uneconomical.

The collection of wild spat is highly dependant on local conditions and a successful farm manager will be able to judge when conditions for spatfall are optimal, and time the collection appropriately. A wide variety of materials are used for spat collection dependant on local availability, durability and cost. In the Far East bamboo poles are used in a similar way to the bouchot method, whereas the most common method is the use of ropes. This is mainly due to their relative cheapness and availability. Natural fibres are excellent for the collection of spat as the hairy nature provides an admirable substrate for settling. In the more developed countries, synthetic ropes are used due to their increased durability. Although they may not be as attractive to the spat as the natural fibres, settling on synthetic ropes can be increased by inserting lengths of unravelled rope to create crevices in which the spat can find shelter. The collecting ropes are attached to longlines or rafts, similar to those used for on-growing. The spat are removed from the collecting ropes when they reach 10mm SL and are placed in mesh sacks which are then attached to the culture ropes. The spat migrate out of the sacks and settle on the ropes using their byssus and are then cultivated as previously described.

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Environmental Impacts

The impact on the marine environment and ecosystems associated with suspended mussel culture is covered more extensively than most shellfish groups, the only exception perhaps being shrimp. There are many conflicting results in the literature and this stems from the characteristics of each individual test area. The main concern with suspended culture is a predicted increase in sedimentation beneath the rafts and longlines, caused by reduced flow because of the suspension structure, and increased levels of faeces and pseudofaeces from the mussels and associated epibiota. Generally investigations into the effects of suspended culture on sedimentation rates have shown that the effect is minimal and that the risk of adverse effects is low (Grant et al, 1995; Jeffs et al, 1999; Crawford, 2001; Crawford et al, 2001; Crawford, 2003; Crawford et al, 2003; Danovaro et al, 2004) although there are examples of suspended mussel culture having adverse effects on the local ecosystem (Freire et al,1990; Stenton-Dozey et al, 1999).

Hartstein and Stevens (2005) showed that there was no significant difference in sedimentation rates between farm and control sites in Marlborough Sound, New Zealand. They did however; find a significant difference in the total organic matter (TOM) between farm sites and control sites in sheltered bays. There were no significant differences between farm and control sites in more exposed areas, illustrating the importance of local hydrodynamic forces on the effects that aquaculture can have on the local environment. Increases in sedimentation have been attributed to the presence of mussel culture by several authors (Dahlbäck & Gunnarsson, 1981; Grant et al, 1995; Chamberlain et al, 2001; Giles et al, 2006). The increase in sedimentation below mussel culture is due to the excretion of faeces and pseudofaeces by mussels and the associated epibiota which grow amongst the mussels. The faeces are characterised by high levels of organic matter and phaeaopigments. Biodeposition can alter the characteristics of the sediment below culture systems. Sediments below culture sites tend to be characterised by finer grain sizes and increased silt/clay content, with decreased porosity and water content (Giles et al, 2006). Faecal based sediments are also characterised by increased C:N ratios and increased organic content (Christensen et al, 2003). An increase in sedimentation and change in sediment character does not constitute a failure to meet the criteria of Principle 2, and as such the impact on the environment could comply with the criteria. However, the sediment can itself affect the ecosystem and these effects are now considered separately.

A change in sedimentation rate and sediment characteristics can potentially lead to a change in the macrobenthic community below culture systems. A study by Giles et al (2006) showed that although there was a significant difference in sedimentation rate, the benthic macrofaunal community was not significantly effected, along with molar C:N ratio, and organic matter content; a fact mirrored by other investigations (Grant et al, 1995). Stenton-Dozey et al (1999) found that the presence of mussel farms had a significant effect on macrobenthic community structures in Saldanha Bay, South Africa. The general pattern observed under mussel rafts and long-lines is a shift towards opportunistic deposit feeders and carnivores (which scavenge on mussels falling from the rafts). Outside the farm areas communities tend to be dominated by deposit and suspension feeders, although this obviously varies between areas (Stenton-Dozey et al, 1999; Christensen et al, 2003). Trophic webs can also be

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altered by the presence of mussel culture structures. Freire et al (1990) demonstrated how the diet of the Arch-fronted swimming crab, Liocarcinus arcuatus, was significantly affected by mussel rafts in the Ría de Arousa, Spain. They concluded that the change in diet was due to a change in the macrobenthic community, and that the crabs were responding opportunistically to these changes, and taking advantage of the more abundant species below the rafts. Such changes in macrobenthic community and trophic relationships could constitute a failure to meet Principle 2 according to both criteria 1 and 2. There are however conflicting results in the literature, which poses a problem when regarding the culture system as a whole. A study by Chamberlain et al (2001) in southwest Ireland helps to clarify the problem. They compared transects at an exposed site and a sheltered site, and found that there was little difference in species diversity along the transect at the exposed site, illustrating that the farm had little effect. However, at the sheltered site there was a decrease in diversity closer to the farm, and the community was impoverished, becoming dominated by opportunistic, deposit feeding polycheates. In sheltered areas there is little movement of water leading to impacts confined to a localised area. The study by Chamberlain et al (2001) demonstrated little or no effect beyond 40m of the farm site. In exposed areas the sediment arising from mussel culture is likely to be spread over a wider area, although this will have a dilution effect so whilst a larger area may be affected the effect will be reduced. The local hydrographic conditions should therefore be considered before reaching a conclusion as to whether a culture operation is having an adverse impact on the macrobenthic community.

Another concern regarding the effect of mussel culture on the environment is the recycling of nutrients, and the changes to the cycle created by aquaculture operations. It has been noted that aquaculture operations can create a concentration of nutrients in the culture area (Christensen et al, 2003). In the mid-1980 s there was a fluctuation in the meat quality of P. canaliculus, which was attributed to differences in food availability (Kaspar et al, 1985). The shortage in food was linked back to a reduction in nutrients required by phytoplankton, possibly linked to the removal of nutrients by mussel culture. A study by Kasper et al (1985) found that at a reference site 97% of ecosystem nitrogen was found in the sediment, whereas at a farm site between 59% and 71% of ecosystem nitrogen was found in the sediment with as much as 40% being present in the mussels. Although the mussels excrete ammonium which is directly available to phytoplankton and increases primary production, the harvest of mussels leads to an export of nitrogen from the system, resulting in an imbalance in nutrient cycling within the ecosystem. A calculation by Christensen et al (2003) estimated that a harvest of 4200t mussels from Beatrix Bay, New Zealand, would result in an export of ~ 59t of nitrogen. The alteration to nutrient cycles could potentially result in changes to community structure or trophic webs, which could result in a failure to meet criteria 1 of Principle 2. There is no evidence for such an effect although specific research into this area has not been performed. It should also be noted that in areas of enrichment, the removal of nitrogen could be beneficial to the ecosystem. Reviewing the current literature there is no adverse effect on the environment and as such the culture system could comply with Principle 2 with regards to nutrient cycling, however, it should be noted that there is a potential risk.

One of the major problems associated with sediment accumulation below finfish aquaculture systems is the formation of anoxic sediments. The majority of studies concerning mussel culture have demonstrated that the formation of such sediments

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does not occur (Grant et al, 1995; Christensen et al, 2003; Giles et al, 2006 ). There is however one exception where the presence of Beggiatoa spp on the sediment surface was noted, indicated an anoxic environment beneath a mussel farm in Sweden (Dahlbäck & Gunnarsson, 1981). The formation of anoxic sediments creates a significant impact to the ecosystem and could constitute a failure to meet the criteria of Principle 2; however, with the majority of studies failing to demonstrate the formation of anoxic studies it should be considered that Principle 2 could be met in this regard.

SCALLOP CULTIVATION

Of the numerous pectinid species occurring across the globe, only 33 species are viewed as commercially important, 5 of these species coming from European waters. Global scallop culture production totalled 1.3 million tonnes in 2005 (FAO, 2007), a decrease from previous years (reaching 1.7 million tonnes in 1997 [FAO, 1999]). Scallop production is a relatively young venture, starting in the 1930 s in Japan, where many of the major advances were made, particularly during the 1960 s when a rapid decline in wild capture fisheries led to increased concentration on the mariculture of pectinid species, particularly the Japanese Scallop, Patinopectin yessoensis (Spencer, 2002). The Japanese and Chinese continue to dominate global scallop production, contributing 97.9% of global production in 2005 (FAO, 2007). Although many countries have tried to use the methods developed by the Japanese, different species of scallops require specific conditions and have required further research, particularly in the area of hatchery production of spat. Here, methods used in different countries are discussed in order to illustrate the differences, whilst attempting to represent the global picture.

Japanese Culture Methods

Although the majority of scallop production in Japan is concentrated around Patinopectin yessoensis (a cold water species), two temperate species are also cultured towards the southern islands, namely Chlamys senatoria nobilis and Pecten albicans. The Japanese have developed successful methodology for the hatchery production of spat, however it remains relatively expensive and the high abundance of natural spat provides a more economically viable option. Scallops spawn from March to April and spatfall occurs after 5-6 weeks, between April and June, and is largely dependant on the area and local conditions. Following larval development, the spat settle onto suitable surfaces, attaching themselves with byssal threads. This attachment is temporary and is followed by settlement on the seabed. The spat are collected in mesh sacks, filled with monofilament, which are suspended from longlines and deployed in anticipation of spatfall (a method used globally for the collection of wild seed). Spatfall for P. yessoensis can be predicted when approximately 50% of developing larvae reach a size of 200 m.

Spat are removed from the collecting sacks between July and September, when approximately 5mm SL in size, and graded into size groups. At this young stage the spat are placed into pearl nets at around 100 individuals per net, and suspended from longlines. Stocking densities are continuously reduced as the scallops grow and can

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be expected to reach 50mm SL within a year, with survival rates as high as 90%. When the scallops reach 30mm SL in size they can either be placed in lantern nets, again suspended from longlines, for on-growing to market size (100mm SL), which usually occurs within 2 years. Although lantern nets can produce higher growth rates than bottom culture methods, they are also liable to produce misshapen scallops due to the scallops biting each other within the nets. In some areas pocket nets are utilised in a similar way to lantern nets. The pocket nets consist of a vertical netting containing pockets, which is suspended in the water column. Scallops are stocked at densities of 2-3 per pocket and can achieve similar growth rates to lantern nets, whilst utilising two-thirds of the area. The grow out of scallops in lantern nets can be categorised as a type 1 production system as described in the introduction.

Scallops can also be re-laid, or sown , on the bottom for on-growing after dredging has occurred to remove starfish predators from the culture plots. Scallops tend to be stocked at around 5 individuals per m2 and can reach market size in 2.5-3.5 years. Although growth is slower in bottom culture and survival reduced (around 30% for bottom culture) the scallops are not misshapen. Harvesting is usually performed by dredges and can result in up to 80% of the stock being recaptured. The relaying of scallops for bottom culture can be classified as a type 2 production system. As there is no containment of the scallops, it is basically a restocking exercise.

Figure 4: Chilean Scallops (Agropecten purpuratus) being prepared for ear-hanging

culture. The scallops are connected to the rope through a hole drilled into the ear of the shell.

Another method of culture used in Japan is the ear-hanging method (figure 4). This method can only take place in more sheltered conditions away from wave and wind disturbance, and generally takes place in areas with depths of less than 10m. Ear-hanging is labour intensive at the initial phase, as each year-old scallop (40-60mm SL) is attached to a synthetic string or hook passed through a hole drilled into its ear . The scallops are attached to dropper lines, suspended from longlines, and

spaced 8-15cm apart. A longline of 100m can support up to 45 000 shells, a capacity of 3 times greater than a longline supporting lantern nets. Due to the freedom of water flow around the scallops, growth rate, survival and shell shape are all improved

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when compared to lantern net culture, and although initially labour intensive, there is less expenditure on structures and servicing of the culture area. Ear-hanging is similar to lantern net culture in that both systems involve suspension from longlines. The similarity is continued with the classification of ear-hanging under the type 1 production system described in the introduction.

New Zealand Culture Methods

New Zealand is an example of a country where the Japanese methods have proven unsuccessful. Although large amounts of seed from the New Zealand scallop, Pecten novaezelandiae, can be collected using mesh bags, the on-growing of the spat has been plagued with fouling problems. Removal of fouling organisms is labour intensive and has proven too costly to allow intensive culture economically viable. The New Zealand methods have since become extensive and since the early 1980 s the wild caught seed have been sown in the traditional wild capture fisheries around Marlborough Sound. The wild fishery has since been abandoned for a managed fishery, which is funded by a levy placed on the harvested scallops. This is another example of restocking and can be classified as a type 2 production system.

Scottish Culture Methods

Although there are many natural beds of scallops around the UK coastline, the switch to cultivated stocks has centred on Scotland. The main reason for this are the sheltered, clean and cool sea lochs along the west coast that lend themselves favourably to good spat settlement and growth. Initial research focussed on both the King Scallop (Pecten maximus) and the Queen Scallop (Chlamys opercularis), however it was soon realised that the low value of the latter would make cultivation uneconomical. This created a problem for the culturists, as the collection of spat invariably resulted in a mixture of spat from both species, with C. opercularis dominating. A method of separating the two species has now been developed, where a plastic grid is placed in the tank of mixed spat. Due to the more active behaviour of C. opercularis spat the two populations become separated. Following occasional failures in natural spatfall, the industry has looked towards hatchery production of seed as a more reliable source and using the methods outlined by the Fisheries Laboratory in Conwy, North Wales, a successful hatchery has been established in Orkney. Transportation of spat is a risky business, as too much stress can cause high mortalities during transit and lead to low survival once placed into the culture system. In order to minimise the risk to the spat they must be kept cool and moist.

Grow out methods used in Scotland are similar to those in Japan, adjusted for the local conditions, and market sizes are reached in 4-5 years for P. maximus (100mm SL), and 3 years for C. opercularis (60mm SL). As in other scallop producing countries, the Scottish industry has encountered problems with fouling and the high cost of labour and equipment associated with the removal of fouling organisms. Bottom culture is the best way to reduce these costs, however the problem of predation then arises from organisms such as starfish (Asterias rubens), brown crab (Cancer pagurus), and the velvet crab (Necora puber). Utilisation of lantern net culture and ear-hanging results in Scottish culture being classified as a type 1 production systems.

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Environmental Impacts

The overstocking of Zhikong scallops, Chlamys farreri, has been linked to environmental issues in Sishilli Bay, China (Zhou et al, 2006). The main result of these impacts has been increased mortality rates and stunted growth of the scallops themselves. This is an important factor to be considered for all bivalve culture. Bivalves require a high standard of water quality in which to grow, and although they have been shown to improve water quality in heavily polluted waters, these organisms are likely to be unfit for human consumption. It is in the interests of the shellfish farmers to ensure that the water quality around the culture site is of a high quality, and there are often conflicts between shellfish farmers and other water users who locally cause pollution. The presence of scallops has been shown to decrease seston and chlorophyll a concentrations, and increase sedimentation rates. The two trends are connected through the filtration of the water column and the subsequent production of faeces and pseudofaeces (Zhou et al, 2006). It has been noted that overstocking of scallops, and bivalves in general, can have a detrimental impact on the environment, but the general belief is that if the carrying capacity (see conclusion) is not exceeded the benefits of scallop culture systems would far outweigh the minimal costs. There has been no research suggesting that the suspended culture of scallops has a negative impact on the environment and as such, suspended culture could fulfil all the criteria described for Principle 2. The restocking of scallops to enhance wild fisheries may not comply with Principle 2. Due to the harvesting methods of the wild capture fishery, i.e. the use of mechanical dredges, there are many possible adverse effects on the environment. Scallops are dredged using dry dredges, which consist of a steel frame that has steel rings and netting attached. As the dredge is pulled along the seabed the weight of the dredge, and sometimes the addition of steel teeth, dig into the sediment facilitating the capture of the scallops (Messieh et al, 1991). The potential impacts of dredging activity include changes to sediment characteristics, benthic community structure and biodiversity (Jones, 1992).

In parts of the UK, and possibly globally, there are small artisanal fisheries where scallops are collected by divers. Although the scallops are collected from wild populations there is scope for such fisheries to be assisted by stock enhancement through bottom culture. There are no scientific reports regarding the effects of hand collection by divers, but it is likely that any effect will be minimal, as there is no disturbance of the seabed and landings are limited by the weight that can be carried by a diver and the time constraints related to diving activities (C. Pringle, pers. comm.). The method is also very selective as only scallops above the minimum landing size are harvested. If such fisheries were enhanced through bottom culture then they would be classified as type 2 production systems.

ABALONE CULTIVATION

Abalones are gastropod molluscs with the generic name Haliotis, and they possess a shallow, ear-shaped shell with a series of holes along the dorso-lateral margin, through with respiratory tubes protrude (Spencer, 2002). They feed on algae and benthic diatoms by scraping away the layers with their radula, and as such are different to the filter-feeding bivalve molluscs previously discussed. The landings of abalone are a very small proportion of global landing statistics accounting for only

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0.16% of shellfish landings (quantity) in 2005 (FAO, 2005); however they are a highly prized gastronomic delicacy in many countries, particularly in the Far East where they can command a high price (a global average of US$10.57 kg-1 [FAO, 2005]). This high price has made the abalone a strong candidate for commercial culture operations.

The culture of abalone began in Japan at the end of World War II following the collapse of wild fisheries. Originally hatcheries were used to produce juvenile abalone, 15-20mm SL, for restocking into the natural environment (Spencer, 2002). This practice has continued to the present day, however some abalone are now retained and grown-on to a relatively small market size of 50-80mm SL, which can be achieved in 3-4 years. There are three main areas of abalone cultivation; (1) spat procurement (hatchery produced to 8-10mm shell length), (2) growth of juveniles (8-26mm SL), (3) and final ongrowing to market size (26-65mm SL) (Mgaya & Mercer, 1995). Different species of abalone require different conditions and rearing techniques, however the general set up of culture facilities are similar.

Hatchery Procedures

The first step in cultivating a species is the successful spawning, fertilizing and hatching of larvae (Fleming & Hone, 1996). In Haliotis tuberculata spawning can be achieved by placing organisms in individual tanks and exposing them to ultra violet irradiated water (irradiation causes an increase in hydrogen peroxide which stimulates spawning) (Hayashi, 1982). Generally spawning can be induced over a longer time period by conditioning, involving a light regime of 12 hours of light and 12 hours of darkness, in conjunction with filtered seawater at summer temperatures (10-20 C). Conditioning in this way usually takes 1000-1500 degree-days (number of days x temperature above biological zero [7 C in H. tuberculata]) (Spencer, 2002). Eggs usually hatch within 18 hours of fertilization (Hayashi, 1982). Trochophore larvae are transferred into stock tanks containing settlement plates. These plates are conditioned (with a film of benthic diatoms and microalgae) prior to the introduction of larvae in order to provide the larvae with a food source. Following settlement the abalone are transferred to larger vessels for ongrowing to juvenile size or market size (figure 5). The nature of such vessels can vary according to the species being cultivated and the region in which the culture facility exists, typically cages or barrels are used (Fallu, 1991).

Sea Culture

The use of barrels and other such containers suspended from longlines for the growout of abalone is common place and occurs in sheltered bays. The requirements for successful abalone growth are clean waters with low suspended particulate matter. Ease of access is also important in order to service the culture structure and feed the abalone. The barrels used are either purpose built or adapted from other uses, with the ends removed and replaced with a mesh to allow increased water flow through the system. The use of cages is also undertaken in areas of California. The cages contain vertical sheets of plastic which are spaced 20cm apart, which act as a refuge for the abalone. Vigorous aeration below the cages ensure that the inner most levels of the cage receives well-oxygenated water and that waste products are removed effectively. Up to 20 000 juvenile abalone can be stocked in a cage, which is 10 times greater than

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a conventional 250l barrel, and growth rates are said to be 25% better than those achieved from comparable barrel culture (Spencer, 2002).

Figure 5: An abalone hatchery system where the abalone have settled onto plates and are being grown on before being placed into sea culture systems. The tanks are connected to a flow-through system and contain corrugated plastic as a shelter for the abalone.

Picture courtesy of wikipedia.com

Growth rates obtained during culture can vary widely dependant on the environmental conditions, for example temperature and stocking densities. Lopez et al (1998) obtained relatively high growth rates of 3.21, 3.78, and 3.81mm shell length per month at 15, 18, and 22 C respectively, when compared to other authors who have obtained growth rates around 1mm shell length per month (Hayashi, 1982; Kelly & Owen, 2002) although it should be noted that these were laboratory based growth trials. In sea cages in Korea, growth rates of around 0.83mm shell length per month are achieved, when averaged over a yearly cycle. At these growth rate, the juveniles take around 4 years to reach market size (>60mm SL) (Spencer, 2002). Stocking density is also known to affect the growth of abalone and it is generally accepted that lower stocking densities tend towards increased growth, and it is the aim of a farm manager to find the correct balance between optimal growth and optimal economic gain.

Diet

Another important aspect of commercial abalone culture is the use of artificial diets and the sourcing of suitable feeds to optimise growth and reduce economic input. Artificial diets have been studied for over 30 years in Asia (Fleming et al, 1996). Nutritional value is obviously an important aspect of artificial diets, however other factors are equally important, including cost-effectiveness, availability off nutrients,

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stability and palatability. Despite the differences in nutritional requirements between abalone species, proximate analysis of artificial diets reveals that there is a high level of similarity between them (Fleming et al, 1996). In general, an artificial diet for abalone will be high in protein (20-50%) and carbohydrates (30-60%), with low levels of lipids (1.5-5%) and fibre (Wilding, 2006).

Although much of the current research is concerned with artificial diets, there is still interest in the use of cheaper algal feeds. These algal feeds can be found in the natural environments, or more recently, can be cultured, particularly in polyculture systems where algae such as Ulva lactuca are used as effective biofilters. This cheap food source has been found to be an acceptable diet for abalone culture (Shpigel & Neori, 1996), and is sustainably sourced. Other algal species suitable for the culture of abalone include Gracilaria cornea, Hypnea spinella, Hypnea musciformis, and Palmaria palmate (Mai et al, 1995; Viera et al, 2005).

Environmental Impacts

As the production of abalone in a culture environment generally utilises hatchery reared larvae, it cannot be classified under any of the production systems described in the introduction. A new category must therefore be proposed. As the cultivation procedure is closed from the wild population the new category shall be named closed production . Production systems categorised as closed systems should not

involve the use of wild caught broodstock and should utilise hatchery produced larvae. The on-growing stage of production should occur in cages, or similar structures in the natural environment, to prevent escape, or in land based facilities.

There are no known studies into the environmental impacts of abalone culture, and as such it would be inappropriate to comment on whether abalone culture could comply with criteria for Principle 2. Points that can be inferred from the culture methods are discussed here but it is imperative that before decisions are made regarding the environmental impacts of abalone culture that specific studies are made, whether these are field studies or through the use of reliable models. The hatchery production of abalone larvae is now widespread and as such there is no impact on the environment with regard to obtaining larvae. One possible issue that can be raised is the use of algae which is taken from the wild. Whilst algae can be seen as less polluting than formulated diets, the use of algae taken from the wild could affect the local ecosystems by removing an effective filter and basic food source. The switch to artificial diets could also lead to problems with high nutrient loads in effluent waters, although recirculation systems could reduce these effects. The best practice could be to utilise algae which is cultured, as this removes the strain on wild populations and can also be used to reduce organic loads of effluent water, and as such is an excellent candidate for sustainable poly-culture.

CLAM CULTIVATION

Clams include cockles, razor-clams, manila clams, and quahogs among others. The most important of these species in a commercial sense is the Manila clam (Tapes philippinarum) which accounts for 70.57% of all global clam landings (FAO, 2007). The majority of world clam landings come from wild capture fisheries, with many

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stocks being regulated in order to prevent over-exploitation. Regulatory measures are often placed on the fisheries restricting the number of licences issued, gear used, season, minimum landing size (MLS) and quotas. Examples of regulated fisheries are the cockle (Cerastoderma edule) fisheries in the Netherlands and the UK. In some regions of the world there are fisheries for spat which are then relayed in shellfish parks for cultivation, where there is more control over environmental conditions. Quantities of commercially harvested clams are difficult to derive and aren t precisely known as they are often not distinguished from wild caught clams when landed or reported. This problem is compounded by the grey area in defining what is classed as cultivated product and what is classified as regulated fisheries (Spencer, 2002).

Seed Procurement

The source of cultivated clams can come from either wild seed or hatchery produced seed. In general, clam seed is easy to produce in a hatchery, however there are only a few species for which hatchery produced seed is available in commercial quantities. Hatchery production of seed tends to be for species which locally suffer from unpredictable spatfall in the wild. In the UK there is hatchery production of Tapes philippinarum and Tapes decussates (Grooved Carpet Shell) on a regular basis with Mercenaria mercenaria (Hard Shell clam) occasionally being produced (Spencer, 2002). The Manila clam was introduced into the UK and as such is unable to reproduce in the natural environment. The cultivator is therefore reliant on hatchery produced seed, which can be obtained at a range of sizes between 5mm and 30mm shell length.

The collection of wild seed can range from simple hand collection using rakes and sieves to the mechanised use of hydraulic dredges which allow access to deeper water where dense patches of seed may occur. Once obtained, the seed are sown in culture plots at more productive densities; however, in order to obtain improved production levels the stock must be protected from predators. One of the main users of wild captured seed for clam cultivation is China, with the focus being on three main species; the Manila clam, the blood cockle, and the razor clam.

Manila Clams

Shallow ponds are created low on the intertidal zone, each several hectares in area, to collect the settling spat. The ponds are inoculated with algae such as Chaetoceros in order to provide the larvae and spat with a food source. The tidal flushing of the ponds is controlled in order to prevent the loss of larvae, spat and food. The yield of such ponds is typically between 750-1500 clams (5mm SL) per m2. The small clams are re-laid into prepared plots at densities of 180 per m2, and can produce yields of 2-4kg m-2 within a year (Spencer,2002).

Blood Cockles

As with the Manila clam, shallow ponds are used for the collection of spat and initial growout stage. If spatfall is particularly dense in an area then thinning may be required where the spat are re-laid in intertidal beds. Growout is usually around 2 years, with cockles reaching 20mm SL (Spencer, 2002).

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Razor Clams

Plots are conditioned by loosening and smoothing of sediment in intertidal areas. Larval content of the water column is monitored to predict the time of spatfall, and 3-5 months following the predicted spatfall the seed are collected. At this stage they are approximately 10mm in length, and are re-laid into growout beds at a density of 900-1800 per m2. After 6 months the clams have reached 50mm SL and are harvested (Spencer, 2002)

Siting of Grow out Plots

Clam cultivation plots are generally in more sheltered areas away from extreme wind and wave action. Although cultivation is possible in more extreme environments, the structures need to be more robust, with service and labour costs increased. There is also a danger that net-covered clams can be smothered before the problem can be rectified. Access to the culture plots is also an important aspect of site choice. If the sediment is too soft then the use of boats is required to access the plots, whereas harder substrates can support wheeled and tracked vehicles, as in France. Many suitable substrates can be found in estuarine areas, however some species such as the Manila clam and the Palourde prefer salinities above 24 psu, and as such are not suited to estuarine areas where the salinity is likely to drop below this level on a daily basis. Although clams can grow effectively high on the intertidal zone, improved growth is achieved further down the shore where they are covered by water for longer periods and hence feeding for longer periods.

There are different methods of grow out for clam cultivation, each being categorised under a different production system described in the introduction. The simplest form of culture is the re-laying of spat into culture plots. With little or no modification to the plots such methods can be classified as type 2 production systems; i.e. restocking. The use of growbags to culture clams, generally on trestles, can be considered as type 1 production, with wild harvested spat being cultured through a grow out phase. The final method is similar to re-laying spat in the sediment; however the use of netting to reduce predation creates a favourable environment and can be classified as a type 3 production system.

Environmental Impacts

Little attention has been paid to the environmental impacts of clam cultivation, and although analogies can be made to other cultured species that have been more extensively researched, it should be noted that there are likely to be differences and that such analogies can only suggest possible impacts, and the actual effects should become the focus of future research. The anticipated environmental impacts caused by the cultivation of clams can be separated into three main areas; 1. The effects of collecting spat from wild populations. 2. The effect of stocking clams at high densities on the local ecosystem. 3. The effect caused by harvesting the clams.

There is little research into the effect of removing spat from the natural populations to support clam cultivation, although evidence from mussel studies suggest that if too much of the natural spatfall is removed natural populations fail, causing increased mortality in organisms which predate in them. An example of this is the increased mortalities of eider ducks witnessed in the Wadden Sea, the Netherlands, in 1990 and

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1991, following the removal of the natural spatfall (Kaiser et al, 1998). The removal of clam seed by hydraulic dredges could potentially damage the benthic ecosystem and the communities residing there, although it should be noted that there has as yet been no research into such activities. In the UK the majority of clam seed is produced by hatcheries and thus removes the problems associated with wild spat collection. The use of hatchery seed will allow the spat procurement phase to comply with Principle 2. Further research is needed in order to assess whether wild collection of spat could comply with the criteria for Principle 2.

The on-growing of clams occurs either in or on the bottom, and as such results in a lower stocking density per m2 of seabed than that of mussel culture. It is possible however, that similar effects associated with sedimentation and removal of phytoplankton (and nutrients) could occur. A study by Mojica and Nelson (1993) investigated the effect of Mercinaria mercinaria culture (in growbags) in a lagoon in Florida. Results indicated that, as with mussel culture, the sediment below the culture system had a lower mean grain size than the control sites, with an increased percentage silt/clay component. The redox layer was also much shallower within the farm site at 0.5mm, compared to 24.33mm and 16.5mm at the control sites. The study showed significant variation in nutrient and plankton concentrations between the sites, although no trend could be detected. No significant effect on the benthic community was detected although there was a reduction in seagrasses within the culture site. The authors concluded that, although the significant change in sediment characteristics could potentially alter the ecosystem dynamics, such alterations were not evident and that there were no negative impacts on the environment from the culture site. It should be noted that no stocking densities were given and that an increase in intensity could result in negative impacts. A negative impact on seagrass beds could potentially lead to a failure to meet the second criteria of Principle 2, as many seagrass beds are endangered or protected habitats. The seed for this operation were produced in a commercial hatchery and harvest was by hand, by removal of the growbags. Such activities are likely to cause minimal environmental impacts, if at all.

With regards to growbag culture, impacts from harvesting are likely to be minimal as bags are removed by hand, with the possible assistance of motorised vehicles to carry the bags to shore. Such activities limit the effects of trampling to small tracks between the rows of growbags. With harvesting likely to be limited to a yearly activity at its most frequent, recovery of these tracks is likely to be rapid. Such production systems will comply with the Principle 2 criteria and could be seen as sustainable.

Harvesting of cultured clams has received little attention from researchers, although the effects of the different harvesting methods can be inferred from other harvesting activities. This is especially true for the hydraulic dredging of clams from sediment, which has received considerable attention regarding the wild capture fisheries. The hydraulic dredge works by blasting water infront of the dredge, which liquefies the sediment allowing a blade to cut through it and harvest the clams (Messieh et al, 1991). The action of the hydraulic dredge has a significant impact on the physical appearance of the sediment and on the benthos. The sediment is left scarred and the scars, which can be detected with side-scan sonar, can remain there for long periods of time (over 3 months [Thrush et al, 1995; Curry & Parry, 1996]) and if harvesting is repetitive on a short timescale, full recovery may never be achieved (Jones, 1992).

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Other impacts that can occur include; increased mortality and damage to non-target species, increased predation of infaunal species due to increased exposure, changes to the chemical and physical characteristics of the sediment (Messieh et al, 1991). Such dramatic changes to the sediment or the benthos are unlikely to be covered by the criteria of Principle 2, therefore harvesting by hydraulic dredge could result in a failure to comply with Principle 2.

A further cause of impacts worth mentioning is the structures associated with the culture of clams. When clams are re-laid into the sediment they are vulnerable to predation. Netting can be placed above the clams to reduce mortality from predation, but such activities can potentially affect sedimentation and local hydrography. A study by Munroe and McKinley (2007) demonstrated that although the netting appeared to increase the population of clams there were no significant effects on sediment composition. An increase in organic carbon was detected beneath the netted areas, but this was attributed to the increased density of clams beneath the netting, rather than increased sedimentation caused by the structure itself. They concluded that the netting had little effect on the environment and that increases in sedimentation noted in other studies are likely to be due to the individual oceanographic characteristics of each site. As the netting is not having an effect on the ecosystem or the benthos the use of netting could comply with the criteria for Principle 2.

OYSTER CULTIVATION

Oyster cultivation is centred on one main species, the Pacific Oyster, Crassostrea gigas, a cupped oyster. Originally from the western Pacific, C. gigas has been introduced to almost all areas of the globe whether it was intentionally or unintentionally. Between the 1920 s and 1960 s several consignments of oysters were introduced to the USA and Canada and they have since established natural populations and now support fisheries. France imported Pacific oysters in the 1960 s and 1970 s to support its Portuguese oyster fishery which was affected heavily by disease during this period. Natural populations have now established along the French coast op to the Brittany peninsula and now supports a successful spat collection each year, which when grown on in trestles result in annual landings of 140000t (Spencer, 2002). It has not always been a welcome introduction however, due to its success in the natural environment it is causing problems in Australia where it is competing for resources with the Sydney Rock Oyster, with similar problems being encountered in New Zealand. In the UK Pacific oysters were first introduced from Portugal in 1926 to the River Blackwater in Essex as a cultivation crop. Having established that conditions in the UK would prevent the establishment of wild populations, broodstock was sent to hatcheries across the country to widen the area where oyster cultivation could take place.

Although landings of flat oysters are low throughout the world, they are highly sought after gastronomically, and can command a higher price than the cupped oysters. The UK once had large populations of the European flat oyster, Ostrea edulis, which supported successful fisheries. They have since been decimated by the disease bonamiasis. This disease is caused by the microscopic organism Bonamia ostreae, which invades the blood cells of O. edulis, causing mass mortalities in the UK, Ireland, France and the Netherlands.

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Flat Oyster Cultivation

Although greatly reduced by disease, the high market price of flat oysters supports small operations in Europe and New Zealand. In England the main fisheries are in the Solent and in the River Fal, Cornwall, with a derived fishery in Essex using seed re-laid from the two former sites. Techniques used to culture flat oysters have remained relatively unchanged since the 19th century. In order to encourage spat settlement lime is placed in areas of the lower shore where settlement is known to take place. Originally the lime was in the form of roofing tiles (and this practice persists in some areas of France), before cheaper alternatives were discovered including old mussel and oyster shells. In Norway, Italy and Croatia the use of bundles of twigs is still used to collect spat, with new materials being investigated. Once the spat have settled they are removed and placed into mesh bags for continued growth. These culture systems are categorised as type 1 production systems.

Cupped Oyster Cultivation

The cultivation of cupped oysters is the most commercially important and widespread of all oyster culture. Naturally warm water species they have been transferred to many other countries as previously described. There are a variety of growing methods used across the globe based on either traditional methods or more modern methods developed and copied from the methods of other countries.

Hanging Culture

Originating in the 1920 s this is one of the oldest of the modern methods, although its use today is decreasing with new methods using its basic principles proving more successful. The hanging method uses scallop or oyster shells threaded onto a wire or ren , which are suspended from bamboo frameworks placed near the low water mark.

Spat settle on the shells and grow in a three-dimensional environment which tends towards increased growth and fattening. This method also removes limitations with type of seabed and can be placed below the low water mark, allowing increased feeding and avoidance of benthic predators. Following settlement the oysters are placed on racks positioned progressively further up shore for a period of 6 months, during which time hardening occurs, before returning to the low shore for ongrowing to market size. Hanging culture is another example of a type 1 production system.

Raft Culture

Typically, rafts of 20m x 10m, made of bamboo, are linked together in chains and anchored to the seabed. To the structure 1200 rens are suspended, each approximately 2m long and holding 60-70 shells. Deployment of the rens is assisted by sampling the water for the presence of eyed larvae, indicating that settlement is imminent. As with hanging culture the young oysters are placed along the higher shore for a period of hardening before they are returned to the rafts. At the on-growing stage the oysters are restrung 20cm apart on a 9m wire and placed in deeper water. Similar to hanging culture this is another example of type 1 production.

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Longline Culture

Longline culture consists of two parallel ropes anchored at each end by concrete blocks and suspended by a series of buoys, whose number depends on the load of oysters being cultivated. As with raft culture, shells with settled spat are suspended from the ropes. The advantage of longline culture over raft and rack culture is the ability for the equipment to be placed in more exposed conditions offshore, and the majority of longline farms exist in coastal rias and offshore. Longline culture is a type 1 production system.

Rock Culture

Typically a Chinese method of cultivating oysters, rock culture involves the deployment of large stones and boulders, often in bridges to raise the oysters off the seabed. The stones are frequently marble, which is cleaned and covered with lime to encourage settlement. As many as 60 000 stones can be placed in a hectare and can produce up to 3t of flesh. For the culture of Crassostrea ariakensis, lime tiles are used for the settlement of spat. These tiles are easily moved and can be thinned out during the grow out process to prevent overcrowding and so maximise the yield obtained from each spatfall. The grow out of C. ariakensis takes 4 years and with up to 145 000 tiles per hectare, yields of 15t of oyster flesh per hectare can be obtained. Rock culture is considered to be type 3 production, since the rocks modify the natural habitat to encourage settlement and improve growth of the oysters.

Stake Culture

Used in areas with a soft substrata, stake culture involves the use of 1.2m stakes, 20-30mm in width, placed in a variety of patterns in the seabed. Initially the stakes are placed in bundles until spat have settled on the surface, at which point they are thinned out and placed into grow out patterns. The grow out period is about 18 months and yields around 0.5t per 10 000 stakes, up to 6t per hectare. Stake culture is similar to rock culture in that there is modification to the natural environment to improve settlement and growth, and as such is classified as type 3 production.

Trestle Culture

Both spat procurement and grow out can be performed on intertidal trestles, which are 3m long and 0.5m high. For spat collection the trestles can hold a variety of settlement surfaces from traditional stones and slate to more modern materials such as PVC tubes, which have a corrugated surface to improve settlement. Spat are removed from the collectors at 20-30mm shell length and placed into bags, called pôches in France, which are 1m long and 0.5m wide. The oysters are initially stocked at 5kg per bag, which results in a yield of 15-20kg per bag. The trestle method is the most commonly used method for culturing Pacific oysters in France (figure 6). Trestle culture is another example of a type 1 production system.

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Figure 6: The cultivation of oysters using trestles in Belon, France.

Picture courtesy of wikipedia.com

Stick Culture

The Sydney Rock oyster is a species typically grown using stick culture. An intertidal method of culture, it comprises of hardwood sticks coated in tar to resist boring organisms. The sticks are 180cm long x 2.5cm square cross-section, and are secured in layers on to a frame to create a crate , which is in turn secured to a rack positioned close to low water in spat collecting areas. Spat settle and attach directly to the sticks, and once the spat have grown to 2-3cm SL and are more resistant to predators, the sticks are removed from the crates and laid individually on the racks, about 20cm apart. The oysters reach market size in approximately 1-2 years, and when the oysters are harvested they are graded for plate or bottling, with smaller oysters being reattached to the sticks to continue grow out. Some farms remove the oysters at a smaller size and complete the grow out process with 3-15 months in trays, producing a better shell shape and improved flesh content. Stick culture could fall into type 3 production as the grow out stage takes place on the same structure as the settlement stage, however the structure is rather complex with modifications occurring throughout the grow out process, and as such is more likely to be considered type 1 production.

Ground Culture

Along the Atlantic and Gulf coasts of the USA American oysters, Crassostrea virginica, are fished from public grounds rather than cultured on private plots; however some additional materials are added to the environment to improve the productivity of the fishery. The use of cultch (shell fragments obtained from processing facilities or dredged from the seabed) enhances the seabed to improve settlement of spat. Once the spat have settled a variety of methods can be used for the grow out of the oysters as described above, however some are left on the seabed to support the fisheries and continue to grow on the cultch. The growth of oysters on

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shells is common in many species and this can lead to the formation of reefs. These reefs were once extensive across Chesapeake Bay, USA, before over fishing and pollution decimated them. Ground culture consists of two production types. Ground culture that continues throughout the grow out stage is type 3 production, since the addition of cultch is an environmental modification. If other grow out methods are used, then the culture becomes type 1 production.

Environmental Impacts

The anticipated environmental impacts caused by the presence of oyster culture operations are similar to those of mussel culture, as both bivalves can be grown in suspended or bottom culture. The presence of oyster rafts has been shown to alter the characteristics of the sediments below the farms (Hayakawa et al, 2001) although the effect of such a change in sediment character was not considered. The use of a model by Chapelle et al (2000) illustrated that in an enclosed Mediterranean lagoon, an oyster farm led to increased ammonium concentrations, and decreased concentrations of phytoplankton, zooplankton and oxygen. The increase in ammonium was attributed to direct excretion by the oysters, with decreases in plankton and oxygen due to filtration and respiration of the oysters. As has been found in other studies, sedimentation was greater in the area of the farm, leading to higher levels of organic matter. Using the model, Chapelle et al (2000) found that by halving the oyster biomass, there was an increase in phytoplankton and zooplankton. They also illustrated a change in the dominance and succession of both phytoplankton and zooplankton and this is likely to be due to a shift from oyster predation to zooplankton predation on the phytoplankton. An alteration in phytoplankton and zooplankton concentrations represents a shift in the trophic balance within the ecosystem and as such may result in a failure to comply with criteria 1 of the MSC s Principle 2.

Cultivation of oysters, namely Crassostrea gigas, has been shown to affect the macrobenthic community. De Grave et al (1998) took samples from a trestle culture site, from both beneath the trestles and the access lanes, and compared the results to samples from a control site. The diversity of organisms beneath the trestles was lower than the control site, with lower numbers of individuals and a lower number of species. The samples from the access lanes, however, showed an increased diversity when compared to the control site. De Grave et al (1998) concluded that the presence of oyster trestles, whilst not increasing the organic content of the sediment, induced a slight shift in total species and displaced some species. It was also noted that the trestles acted as a refuge for mobile scavengers such as Carcinus maenas and Paleamon serratus as few were found on open sand compared to larger numbers beneath the trestles. Results from this study suggest that although there is a minor effect on the benthic community structure, there is still a stable community present and when compared to other aquaculture systems the effects are negligible. A decrease in biological diversity could constitute a failure to comply with the second criteria of Principle 2. Although it should be noted that the area under the trestles which exhibits a decreased biodiversity is only a small area of a wider ecosystem, and if the ecosystem were considered to include the areas outside of the farm then the effect is likely to be negligible. Providing that culture sites do not dominate an ecosystem, then the second criteria could be met and Principle 2 complied with.

A major impact of oyster culture on the environment is the use of Carbaryl, a broad spectrum pesticide, which is used in the USA to control burrowing shrimp

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populations. There are two species of burrowing shrimp, Neotrypaea californiensis and Upogebia pugettensis, which burrow into the mud beneath oyster reefs in the Pacific Northwest region of the USA (Dumbauld et al, 2006). The Carbaryl is added to the sediment every 6 years as part of ground cultivation plot preparation (Simenstad & Fresh, 1995). The use of Carbaryl can potentially alter the community structure and trophic web and could result in a failure to comply with Principle 2 criteria.

There are also positive impacts of cultured oysters, as with other bivalve mollusc culture, which are often overlooked. Oysters are efficient filters of the sea and can remove heavy metals, organic matter, suspended solids and phytoplankton, which can be especially useful in heavily polluted waters and eutrophic conditions. Oyster reefs have been shown to effectively remove faecal coliform bacteria and chlorophyll a (in the form of phytoplankton) from the water column, and form an important part of the nutrient cycle releasing ammonium into the environment (Cressman et al, 2003). It should be noted that oyster beds were once much more prolific (Keiser et al, 1998) and as such their re-introduction into estuaries could be an effective way of resetting the balance of these ecosystems by removing urban and agricultural waste entering the marine environment through the rivers and runoff. An example of how prolific oyster beds were in previous times is illustrated in Chesapeake Bay, USA. The estimated biomass of oysters occurring in the bay pre-1870 was 188 x 106 kg (dry weight) and the oysters could filter the entire volume of water within the bay in 3-6 days. The biomass in 1988 was calculated at 1.9 x 106 kg (dry weight) and the turnover time had increased dramatically to 325 days (Newell, 1988). The dramatic decrease in oyster biomass has been attributed to continued overexploitation by capture fisheries and by the pressures of disease. The result of the dramatic decrease has been the formation of an anoxic layer below the pycnocline during the summer months. The re-introduction of oysters would help to reverse these effects through their role as a major benthic-pelagic coupler (Mann, 2000), and is an example of how the enhancement of shellfish fisheries and shellfish culture can improve the natural environment and stabilise endangered ecosystems.

Oysters have also been shown to successfully reduce the organic load in aquaculture effluents. The Sydney Rock oyster, Saccostrea commercialis, reduces the total suspended solid (TSS) content of shrimp pond effluent to 49% of initial levels when stocked at high density (Jones & Preston, 1999). Such studies show promise for the poly-culture of oysters with other commercially cultured species, reducing the environmental impact of the operation and increasing the economic gains. The use of pearl oysters to remove heavy metals has been investigated and illustrates a method of aquaculture to improve the environment whilst producing an economically viable product without the concerns over human consumption (Gifford et al, 2004). The production of pearl oysters could comply with the criteria for Principle 2, although whether the flesh would be edible is not the focus of this report and would be dependant on the level of pollution in the locality of the culture site.

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CRUSTACEAN CULTURE

CULTIVATION OF CLAWED LOBSTERS

The cultivation of clawed lobsters involves two species; the American lobster, Homarus americanus, and the European lobster, Homarus gammarus. Technically the culture of homarid lobsters is simple, however problems arise throughout the culture process with cannibalism and fighting, resulting in the need to individually confine the lobsters.

Broodstock

The use of wild caught broodstock is common place and relies on either the capture of berried (egg-bearing) females, or the conditioning of females in captivity. The former is the easiest method of obtaining eggs, however the landing of berried females is prohibited in many areas as a conservation measure and licences are required. The mating of captive broodstock can be achieved using natural copulation of intermoult females, or through artificial insemination. Once lobsters have been acquired they can be stored either at sea in boxes moored to buoys or in land-based pond facilities, which provide easier access. In the land-based systems the lobsters are held in communal tanks, with hides added to provide refuge for the lobsters and reduce stress. Various hides have been tried and tested and a popular choice is the use of concrete ridge tiles (Burton, 1992). To prevent fighting between the lobsters the claws are banded (Europe) or pegged (USA). Pegging involves a small wooden peg being inserted into the articulation joint, preventing the use of the claw, although it should be noted that this can lead to increased susceptibility to infection (Lee & Wickens, 1992).

Spawning and Incubation

The conditioning of lobsters for spawning and incubation differs between the two Homarus species. The National Lobster Hatchery, Padstow, Cornwall, follows the procedure described by Burton (1992) (D. Boothroyd, pers. comm) where lobsters are acclimated to 16 C and held at this temperature during the incubation process. The salinity is maintained above 30ppt. If the temperature is raised above 16 C the larval development time is reduced, however the survival rate of the larvae is also reduced.

Environmental conditions are important for the success of attachment of eggs to the pleopods following spawning. Homarus americanus is held at winter temperatures (0-5 C) for 5 months prior to spawning to improve this attachment, although for reliable spawning the lobsters have to be exposed to this conditioning for a number of years. An incubation period of 4-18 months, depending on temperature, follows spawning. The development of the eggs during this time can be monitored by the colour change that occurs, and later by the size of the eye of the developing larva. By monitoring in this way the hatching time can be predicted to within a few weeks.

Hatching

The period of hatching usually lasts 3-5 days, with the first eggs from a brood likely to be more robust than those hatching later. Often only the larvae which hatch in the first couple of days will be used in culture as the rate of mortality for the later

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hatching larvae is too high. The number of larvae produced is variable and dependant on the size of the female. Lee and Wickens (1992) report that typically females in the range of 450-1500g will produce 800-13000 larvae each, whereas Burton (1992) found that female H. gammarus produced between 1000 and 2600 larvae each. The free-swimming larvae are collected by passing a current through the incubation chamber and allowing the larvae to pass into a separate container with a 1.5mm mesh. Whilst the hatching of eggs form wild caught larvae is successful and appropriate for small scale culture and research, a larger operation is likely to require eggs on a more regular basis and will need to employ the use of conditioned broodstock to produce larvae outside of the natural season.

Larval Culture

Larval culture takes place in upwelling tanks ranging from 40-80 l capacity, which can be linked together in a recirculation system. The length of the larval phase is largely dependant on temperature; at 18 C the larval stage of H. gammarus lasts for 14-18 days, with metamorphosis lasting up to 10 days. Initial stocking densities are approximately 2000 larvae per 80 l tank (Burton, 1992). During the larval cycle a variety of diets can be used including live and frozen Artemia, frozen Mysid shrimp, chopped molluscs or artificial feeds. The most favoured feed is live Artemia, since dead and formulated feeds can lead to increased organic concentrations in the water and reduce water quality. At the National Lobster Hatchery a diet of enriched Artemia supplemented with frozen Mysid shrimp (D. Boothroyd, pers. comm.). Lighting is important in the survival of the larvae, with dim light being preferred to complete darkness. Heavy mortalities can occur between stage 4 and stage 6 of larval development, and as with initial hatching of larvae, it is suggested that only the earliest larvae to reach stage 4 be kept for further culture. The separation of stage 4 larvae from the stage 3 larvae is a labour intensive, but important part of the culture process as cannibalism is extensive at this stage.

Nursery

If reared communally, juvenile lobsters are likely to fight, intimidate and cannibalise each other, leading to increased heterogeneity of growth, increased mortalities and increased numbers of crippled of damaged individuals. Although cannibalism occurs throughout the larval cycle, at the nursery stage of culture this becomes unacceptable as it can be more easily avoided. Typically, the juvenile lobsters are separated by plastic dividers which allow the flow of water through the tank whilst confining the lobsters to individual compartments. Such dividing systems must meet certain requirements. They must not restrict the growth of the lobsters, and as such they must be changed throughout the culture period. The compartments must also allow access of oxygenated water, be self-cleaning and be suitable for the application of automatic feeding. One suitable system that has been developed is the use of racks of mesh cages which are placed in a tank. Live Artemia are added to the water and can pass through the mesh where they can be preyed upon by the lobsters. The drawback with such systems is that the mesh allows the lobsters to access neighbouring cells with their claws which can lead to fighting and intimidation, albeit at a reduced scale when compared to communal rearing. In confined conditions survival rates of 80% or greater can be obtained (Lee & Wickens, 1992). The National Lobster Hatchery uses a system of troughs containing plastic dividers with a mesh base. Each cell contains a

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post-larval lobster, which are fed a commercially available formulated diet (D. Boothroyd, pers. comm.).

On-growing

The on-growing of lobsters to market size takes place in battery systems similar to nursery culture where the lobsters are individually confined. The design of these culture systems is centred on four main factors; (1) Sizing of compartments in order to prevent retardation of growth and to minimise the number of changes made throughout the culture period, (2) use of cost-effective materials for container production, (3) removal of wastes and adequate water exchange in each container, (4) rapid and accurate distribution of food to each container. Some of the designs currently in use include troughs divided into compartments using plastic dividers and mesh screens through which water freely flows; Rectangular tanks in which blocks of containers are placed. The containers have perforated floors allowing the flow of water through specialised flushing systems.

Feeding through the on-growing stage can be separated into two stages. Smaller lobsters of up to 20mm carapace length (approx 4 months old) can be fed live Artemia and reared in systems similar to the mesh cage design described in the previous section. Larger lobsters can be fed on a variety of different diets including formulated diets, frozen and fresh natural foods.

Figure 7: A juvenile lobster reared at the National Lobster Hatchery, Padstow, Cornwall, released into the natural environment as part of the hatcheries restocking programme.

Picture courtesy of D. Boothroyd, National Lobster Hatchery, Padstow, Cornwall.

Ranching

There are several examples of hatchery produced juvenile lobsters being released into the wild to help support wild capture fisheries. One such example of a ranching project is the National Lobster Hatchery in Padstow, Cornwall. The hatchery grows juvenile lobsters up to the age of 3 months (figure 7) in using methods previously described. The juvenile lobsters are then released onto specified lobster grounds around the Cornish coast where they grow and support the local fishery, enabling it to become sustainable. The use of hatchery reared juveniles to enhance wild populations falls under the second production system described in the introduction.

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Environmental Impacts

There is little impact on the environment from the National Lobster Hatchery system. The hatchery utilises a recirculation system, and has a water exchange of approximately 10% per week, with water being filtered prior to release into the marine environment (D. Boothroyd, pers. comm.). The use of wild broodstock would potentially effect the wild population if the lobsters were to be grown on to commercial size. However, the hatchery operation is concerned with restocking the natural populations and as such, there is an improvement in the natural population, since survival rates in the hatchery are higher than those expected in the wild. By using naturally sourced lobsters there is no genetic impact on the local population. If broodstock were brought in from further afield there could potentially be an effect on the local genetic pool. There is no conflict with the criteria for Principle 2 and as such the production of lobsters for stock enhancement programs can be seen as a sustainable practice.

CULTIVATION OF SPINY LOBSTERS

The Panulirid lobsters that are cultured include the Western rock lobster (Panulirus Cygnus), California spiny lobster (P. interruptus) (figure 8) and the Japanese spiny lobster (P. japonicus) amongst others. Two other species of spiny lobster are also cultivated, namely the red and green rock lobsters (Jasus edwardsii, J. verreauxi). Two main obstacles need to be overcome when cultivating spiny lobsters. The first is the rearing of phyllosome larvae, which encounters technical difficulties. There is also a problem with a shortage of juvenile lobsters for fattening.

Figure 8: A mature Californian spiny lobster, Panulirus interruptus, in its natural environment.

Picture courtesy of wikipedia.com

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Broodstock and Spawning

Breeding tends to be reliant on natural spawning methods. Males and females are kept together in broodstock tanks until the females spawn, at which point they are removed and placed into individual tanks until the eggs complete development and phyllosoma are released. The female is then reintroduced to the broodstock tank where further mating can take place. Murugan et al (2005) produced 3 spawnings in a 6 month period with a single pair of lobsters. It is believed that with commercial numbers of broodstock, phyllosoma can be produced throughout the year (Vijayakumaran et al, 2005). It should be noted that in a commercial environment, lobsters grown for consumption rather than broodstock should be separated into male and female groups to prevent mating, as this decreases growth rates and weight of the individual lobsters.

Larval Culture

The main problem concerning the larval culture of spiny lobsters is the length of the pelagic stage, which can last up to 10 months. During the phyllosoma stage there can be between 9 and 29 instars, depending on the species being cultured. The phyllosoma are fragile and susceptible to damage and infection if water quality is not of the highest standard. Each species has its own specific cultivation requirements; however the following account is a generally recognised methodology. The culture vessels are keisel style tanks with an upwelling system to maintain the larvae in suspension. The water can be inoculated with microalgae such as Chaetoceros spp. and supplemented with mussel gonad tissue or live Artemia. Three main feeds are used in larval rearing. The first is the use of Artemia, with nauplii being fed to early instar stages, and adult Artemia being fed at later stages. Mussel gonad tissue is also a popular choice of food. It is chopped and added to the culture medium. There are problems associated with feeding mussel flesh to the larvae, concerning water quality. It has been noted that the flesh can become entangled on the pereiopods, leading to deterioration of water quality (Kittaka, 1997). The final diet which can be used successfully is fish larvae, for example the larvae of Arctoscopus japonicus. The problem with using fish larvae is the question of sustainability. Care should be taken if obtaining larvae from natural sources that the natural population will not be adversely effective.

Survival rate of larvae is dependant largely on water quality within the system and the contamination of the system with microorganisms. Contamination can occur for a number of reasons such as seawater source, phyllosoma density, food source, microalgal concentration etc. The exact effects of inoculation with microalgae is not known, but it is evident that there is improved water quality when microalgae are added to the culture medium (Kittaka, 1997)

On-growing

One method of on-growing juvenile Panulirus spp., whether they be wild caught or hatchery reared, is to use portable containers which can be placed directly into the sea. This method was researched by Lozano-Alverez (1996), using 3m x 3m x 1m cages made from a steel piping frame and plastic-sheated wire mesh. A door at the top of the cage allowed the introduction of lobsters and food to the cage. The results from this trial suggested that the method would be suitable for the fattening of wild caught

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lobsters, or maintaining larger lobsters in times of plenty until numbers start to dwindle. However, the system may not be suitable for the ongrowing of hatchery reared juveniles as after 45 days there was a marked increase in mortality and a reduction in growth rate, possibly caused by fighting and intimidation due to the confined space of the enclosure. The on-growing of spiny lobsters on containers is considered type 1 production.

Environmental Impacts

With little research into the culture of spiny lobsters in general, there is practically no information regarding the environmental impacts associated with their culture. The general concerns are similar to those for crustacean culture in general. In order for commercial culture to become viable hatchery production of larvae must be achieved. Not only is the use of wild caught larvae detrimental to wild stocks, the numbers of wild larvae available are insufficient to support large commercial production operation. One of the major environmental problems associated with shrimp culture is the release of organically enriched water from production systems. Organic enrichment occurs due to high stocking densities and the use of formulated feeds. In order to achieve successful culture of spiny lobsters on a commercial scale the formulation of artificial feeds will be paramount, reducing the use of fresh fish and shellfish (Rimmer, 2006). It is important that the feeds that are developed that are environmentally friendly to avoid the problems that have been experienced in shrimp culture. Not enough research has been conducted to make a definitive conclusion regarding Principle 2 compliance, although without the development of hatchery techniques or a switch to stock enhancement production it is likely that wild caught larvae will be unable to support the industry, and as such there could be failure to meet the criteria of Principle 2.

CRAB CULTURE

The majority of crab culture takes place in the Far East and concerns the culture of the mud or mangrove crabs (Scylla spp.). Other species which are cultured include the blue crab (Callinectes sapidus), the swimming crab (Portunus trituberculatus), and the Caribbean king crab. Originally culture was concerned with restocking the wild fisheries, however in recent years commercial cultivation of Scylla serrata has become an important industry, especially in Taiwan where it has been differentiated into hatchery, nursery, on-growing and fattening operations (Lee & Wickens, 1992). Cultivation takes place in extensive poly-culture or semi-intensive mono-culture systems. The reliance of the industry on wild caught broodstock results in the culture of crabs being classified as type 1 production, although with development of successful hatchery techniques and closure of the lifecycle, a closed production system could be achieved.

Broodstock and Larval Culture

The use of wild-caught broodstock is still common place, and eyestalk ablation allows increased control over the spawning cycle. Larval survival can be as high as 60%, however this needs to be at low densities (6 larvae per litre) since the long spines of the zoeae lead to entanglement, increasing larval mortality. At a temperature of 25-

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28 C incubation will last for 10-15 days. The first zoeae stage larvae are fed minced Artemia nauplii, with later stages receiving a diet of live nauplii. At the first megalopa stage minced fish or bivalve flesh can be fed. Tanks similar to those used for lobster cultivation are used and can be connected to recirculation systems (Lee & Wickens, 1992).

Nursery

Nursery culture tends to take place in earthen ponds of 15-20 m2 lined with a 10cm layer of beach sand. Juvenile crabs are stocked at 2000-3000 m-2 and are held in these nursery tanks for 2 weeks until they reach 1cm carapace width. Crabs are fed a diet of minced trash fish at 1kg per 30 000 crabs. Temperature is controlled by shading, salinity is maintained at around 20 ppt and where possible, water is exchanged at a rate of 1 pond volume per day.

On-growing

The polyculture of mud crabs with shrimp, fish or seaweed (e.g. Gracilaria spp.) is popular in the Philippines and takes place in extensive systems. The juvenile crabs can either enter pond systems from the wild populations or be stocked at 1000 ha-1

using wild caught or hatchery produced juveniles. If intentionally stocked, the ponds will be surrounded by an overhanging fence of bamboo canes to prevent loss of stock. Crabs grow to a market size of 8cm carapace width in around 4-6 months, resulting in yields of around 340 kg ha-1 yr-1. The conditions in these ponds are often governed by the requirements of the species cultured alongside the crabs rather than those required by the crabs themselves (Lee & Wickens, 1992).

Monoculture of crabs also takes place in smaller semi-intensive systems. Earthern ponds of 0.2-0.5 ha are stocked with 0.5-3 crabs m-2. Crabs are fed live snails and trash fish, and grow to 8cm carapace width in 3-4 months during the summer or 5-6 months in the winter. Yields are in the region of 1800 kg ha-1 yr-1. More recently the use of pens and cages has been utilised for the on-growing of portunid crabs. The cages are constructed from bamboo, polyethylene netting or galvanised metal mesh. They are placed in shallow lagoons and ponds and supported in the upper layers of the water. Cages of 3 x 3 x 2m are stocked with 30-60 kg of crab for grow out (Williams & Primavera, 2001).

The most recent development in the culture of Scylla spp. is the integration with mangrove reforestation. During the explosion of shrimp (and crustaceans in general) culture during the 1970 s and 1980 s, large areas of mangrove were removed to make way for culture ponds. In more recent years the consequences (loss of capture fisheries, income for local populations and coastal defences) of such actions have been made clear and reforestation of mangroves is now an important conservation issue in many parts of tropical Asia. The integration of crab culture into reforestation project shows promise of a sustainable aquaculture system, beneficial for both the environment and the local communities (due to the low level of investment required). Pen culture is the main method of integration. The pens are about 200 m2 in size and are placed in areas replanted with mangrove species such as Rhihzophora spp., Avicennia spp. and Sonneratia spp. The design of the pens allows the area to be inundated during the highest tides, maintaining the natural mangrove environment. The pens are enclosed with nylon mesh to prevent the crabs from escaping. Canals

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are dug to a depth of 50cm around the periphery and through the centre of pen enclosure to provide refuge for the crabs at low tide. A mesh screen of 5mm is placed over the drain gates to allow the entrance of juvenile fish and crustaceans, which would naturally use such mangrove areas as nursery grounds. The feed used in such systems is similar to other crab culture with the use of fish by-catch and bivalve flesh obtained locally (Triño & Rodriguez, 2002). Crabs are stocked at 1 crab m-2 and a hectare of these pens can produce yields of 1400 kg (Yap, 1999).

Soft Shelled Crab Production

The market for soft shelled crab is generally small; however as a gourmet food the market for soft shelled blue crab, Callinectes sapidus, is growing. Production is a short term activity and may not involve any feeding of the crabs. Wild caught crabs are held in one of two systems until they moult and take on a soft shelled form. The first system involves floating boxes of approximately 2 m3 holding 200-300 crabs. Added stability comes from a 20cm lip around the edge of the box, however problems can still arise from strong currents, as well as predators. The second method of producing the soft shelled crabs is a shore based method, using tables with a continuous flow of water passing through them and connected to a recirculation system. The typical dimensions of a table are 2.4 x 1.2 x 0.25m, and are filled to a depth of 10cm. The design lends itself to self cleaning, reducing the disturbance to the crabs. Flow rates are typically 3-4 table volumes per hour.

The crabs are caught in pots and traps from wild populations and checked for the presence of peelers or busters . Peelers are identified by a split in the shell along the last pair of pereopods, and are likely to moult in 3-4 days. Busters are identified by a split along the posterior edge of the carapace and moulting is likely to occur within 3 hours. The tables are checked for the presence of busters every 4-6 hours. Busters are removed to moult in separate trays, and once swelling to full size has taken place the crabs are removed from the water to prevent hardening of the shell. If moulting crabs are in short supply, inter-moult crabs can be held and fed until moulting occurs (Lee & Wickens, 1992).

Environmental Impacts

The main environmental impact of crab culture is the procurement of larvae from wild broodstock, and the on-growing of wild crablets. Whilst the crab cultivation industry remains small such impacts are minimised, however expansion of the industry without development of hatchery techniques to provide a reliable source of larvae will lead to over exploitation of natural stocks, potentially leading to the collapse of local fisheries (Williams & Primavera, 2001). Another major issue with the sustainability of crab culture is the use of trash fish. Although the trash fish are often unfit for human consumption and as such would otherwise be wasted, an expanding industry is unlikely to be supported by bycatch alone, and an increase in demand could draw local fishermen into targeting bycatch species to sell to farmers, putting further strain on natural stocks. It should also be note however that poly-culture of crabs with other species is less harmful to the environment than the monoculture of shrimp or fish. The poly-culture with mangroves is also an important economic incentive for the local communities (generally the rural poor) to conserve the mangroves, whilst providing a regular income. Whilst the industry remains small, the adverse effects described are minimal and as such compliance with Principle 2 could be achieved.

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However expansion of the industry is likely to put too much pressure on the wild stocks of crab and trash fish, in which case there could be a failure in compliance to Principle 2.

An issue which has plagued the shrimp culture industry is the release of effluent from farm sites leading to localised eutrophication and organic enrichment. At present crab culture takes place in extensive and semi-intensive systems and as such only low concentrations of organic matter are produced and little is released. In the poly-culture with mangroves, the organic matter is likely to be retained in the sediment by the mangrove plants and aid their growth, further developing the recovery of the ecosystem. With further research into hatchery production of viable larvae and the development of feeds that are cheap, nutritionally suitable and environmentally friendly, mud crab cultivation could become a benchmark for other forms of crustacean culture to aspire to.

CONCLUSIONS

There are a lot of conflicting results within the literature regarding the impacts of shellfish aquaculture on the environment. For every investigation that finds a significant adverse impact, there is another investigation demonstrating no adverse impacts. The conundrum can be broadly explained by one main feature; local conditions. The local conditions can include a variety of other factors, including hydrodynamic conditions, local benthic communities, prevailing winds etc. Local hydrodynamic conditions will control the spread of sediment from a culture site in terms of distance and direction. Generally more sheltered conditions are favoured from a culture perspective, since there is a reduced impact on the culture system from wind and wave action, thus reducing the servicing costs. However, from an environmental impact viewpoint, the more exposed sites are more favourable. With an increase in currents, the extra sediment produced by the culture system will be carried further, and whilst this may appear to be increasing the impact area, the literature shows that the effect on the environment is greatly reduced when spread over a wider area. The importance of local conditions to the effects a shellfish culture site has on the environment can be linked to what is known as carrying capacity . Carrying capacity is one of the most contentious issues in aquaculture currently, and with respect to shellfish culture it can be divided into four sub-categories (McKindsey et al, 2006):

1. Physical Carrying Capacity

the total area of culture operations that can be accommodated in the physical space available.

2. Production Carrying Capacity

the stocking density at which the harvest is maximised.

3. Ecological Carrying Capacity

the stocking density at which unacceptable ecological impacts occur.

4. Social Carrying Capacity

the level of farm development causing effects that are socially unacceptable.

In relation to the current report, the most relevant is the ecological carrying capacity. In simple terms the ecological carrying capacity is the maximum level of production

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that doesn t result in ecosystem degradation, although it must also include the procurement of seed (if from outside the culture ecosystem) and usable area to some degree. Whilst there have been several studies into the production carrying capacity (Carver & Mallet, 1990; Bacher et al, 1998; Bacher et al, 2003) there have been few studies with limited success for modelling the ecological carrying capacity of mollusc culture systems. In terms of decision making regarding the sustainability of aquaculture operations models for ecological carrying capacity should be established and applied to each area, and providing the carrying capacity is not exceeded then the aquaculture product can be regarded as sustainable.

There is legislation put in place by the EU regarding shellfish production and water quality in general. The EC quality of shellfish growing waters directive (79/923/EEC) concerns the protection and improvement of water quality in shellfish waters in order to maintain a high standard of shellfish products for human consumption. The EC Shellfish Directive (91/492/EEC) concerns the quality of shellfish waters and sets criteria for the commercial production of shellfish based on bacterial levels and the degree of contamination by faecal indicator bacteria. The EC Environmental Impact Assessment (EIA) Directives (85/337/EEC amended by 97/11/EEC) require an EIA to be performed for certain projects, dependant on scale, intensity and local conditions (Read & Fernandes, 2003). There are other EC directives applicable to shellfish aquaculture in the EU, however those stated here are the most relevant. In order to meet the criteria for these directives, shellfish farms must ensure that effluent from the farms is minimal and not detrimental to water quality. The use of EIA s ensures that any environmental impacts are anticipated and considered during the planning process, theoretically removing the possibility of shellfish culture sites having negative impacts on the environment. It is in the interest of the shellfish farmers themselves to ensure that water quality remains high in order to maximise growth of their product. The reality is that many shellfish farmers are actually in conflict with terrestrial land users surrounding their farms and associated watersheds as agricultural and urban run-off can cause problems with larval survival, spat settlement and growth rates (S. Kestin, pers. comm.; C. Leverton, pers. comm.).

There are examples of each type of production system proposed by the MSC as described in the introduction within the shellfish production industry. There is also an example of a production system which is not covered by the MSC proposals, that of abalone production. Due to the closure of the life-cycle of the abalone, larvae that are produced in a hatchery can be grown to commercial size without re-introduction to the marine environment and there is no reliance on natural stocks for the procurement of larvae or broodstock. This Closed Production system has been given it s own category, which could be extended to other species and groups once successful hatchery techniques have been developed. A summary of the production systems is shown in table 1.

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Table 1: A summary of shellfish cultivation methods categorised according to MSC production system types. Production systems that are not captured by the categories proposed by the MSC are assigned a new category.

Production System Type 1 Type 2 Type 3 Other

Mussel Bottom Culture

Mussel Off-bottom Culture (E.g. longlines, rafts, poles)

Scallop Bottom Culture

Scallop Suspended Culture (E.g. earhanging, lantern nets)

Abalone Culture Closed Production System

Clam Trestle Culture

Clam Ground Culture

Clam Ground Culture (with addition of netting)

Oyster Bottom Culture (E.g. rocks, stakes)

Oyster Ground Culture

Oyster Off-bottom Culture (E.g. longlines, rafts, trestles, sticks)

Clawed Lobster Culture (Ranching)

Spiny Lobster Culture

Crab Culture

Shellfish aquaculture in general can have many positive effects on the environment. For example, bivalve shellfish are known to be effective filters of the marine environment removing particulate matter and thus reducing turbidity (Shumway et al, 2003; Newell, 2004). There can be positive effects in removing excess nutrients, particularly nitrogen, along with improving critical habitats and aiding the survival of endangered species, for example seagrasses. Whilst there are questioned raised regarding the use of large areas of intertidal and subtidal areas for the culture of shellfish, it should be noted that in the past, shellfish beds covered much wider areas

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and increased culture could be restoring the natural balance (Newell, 1988; Kaiser et al, 1998). As with any organism, an overabundance or overstocking could potentially lead to adverse effects, and it is for this reason that the ecological carrying capacity is an important factor.

Taking into account the literature reviewed in the current report and the positive nad negative impacts that can be associated to enhanced shellfisheries and shellfish aquaculture it is the opinion of the author that there is a strong case for the MSC to consider these production operations for certification. The important factors to remember are that local conditions are critical, and it is advised that each site be modelled in order to ensure sustainability. Monitoring of sites could ensure that criteria continue to be met and that impacts remain within the constraints of the guidelines. The author suggests that the principles may also require some modification in order to capture all possible effects of aquaculture.

ACKNOWLEDGEMENTS

Thanks are extended to the staff of Cornwall Fisheries Resource Centre for the use of their computer facilities. Thanks are also extended to Dominic Boothroyd of the National Lobster Hatchery and to Steve Kestin of Cornish Mussels who provided valuable information regarding commercial operations, and to Dr Tom Pickerell of the SAGB for his guidance throughout the project.

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