Species group report card – marine reptiles...Species group report card – marine reptiles...

Species group report card – marine reptiles

Supporting the marine bioregional plan for the North-west Marine Region

prepared under the Environment Protection and Biodiversity Conservation Act 1999

ii | Supporting the marine bioregional plan for the North-west Marine Region | Species group report card – marine reptiles

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© Commonwealth of Australia 2012

This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from the Commonwealth. Requests and enquiries concerning reproduction and rights should be addressed to Department of Sustainability, Environment, Water, Population and Communities, Public Affairs, GPO Box 787 Canberra ACT 2601 or email [email protected]

Images: Green Turtle – Tourism WA, Loggerhead Turtle – K.Crane, Raccoon butterfly fish – N.Wolfe, Display of colourful coral – Tourism WA, Red and yellow feather star (crinoids) – Tourism WA, Whale tail – Tourism WA, Snorkelling in Ningaloo Marine Park – Tourism WA, Black tip reef shark – N.Wolfe, Whale Shark – GBRMPA, Sea Grass Meadow – Lochman Transparencies, Clarks Anemone Fish – C.Zwick and DSEWPaC

iiiii | Supporting the marine bioregional plan for the North-west Marine Region | Species group report card – marine reptiles

CONTENTS

Species group report card – marine reptiles ..........................................................................11. Marine reptiles of the North-west Marine Region ....................................................................3

2. Vulnerabilities and pressures .................................................................................................10

3. Current protection measures ..................................................................................................21

References ................................................................................................................................23

Attachment 1: Marine reptiles in the North-west Marine Region .......................................32

1 | Supporting the marine bioregional plan for the North-west Marine Region | Species group report card – marine reptiles

SPECIES GROUP REPORT CARD – MARINE REPTILES

Supporting the marine bioregional plan for the North-west Marine Region prepared under the Environment Protection and Biodiversity Conservation Act 1999

Report cards

The primary objective of the report cards is to provide accessible information on the conservation values found in Commonwealth marine regions. This information is maintained by the Department of Sustainability, Environment, Water, Population and Communities and is available online through the department’s website (www.environment.gov.au). A glossary of terms relevant to marine bioregional planning is located at www.environment.gov.au/marineplans.

Reflecting the categories of conservation values, there are three types of report cards:

• species group report cards

• marine environment report cards

• heritage places report cards.

While the focus of these report cards is the Commonwealth marine environment, in some instances pressures and ecological processes occurring in state waters are referred to where there is connectivity between pressures and ecological processes in state and Commonwealth waters.


Species group report cards

Species group report cards are prepared for large taxonomic groups that include species identified as conservation values in a region; that is, species that are listed under Part 13 of the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and live in the Commonwealth marine area for all or part of their lifecycle. All listed threatened, migratory and marine species and all cetaceans occurring in Commonwealth waters are protected under the EPBC Act and are identified in the relevant marine bioregional plans as conservation values.

Species group report cards focus on species for which the region is important from a conservation perspective; for example, species of which a significant proportion of the population or an important life stage occurs in the region’s waters.

For these species, the report cards:

• outline the conservation status of the species and the current state of knowledge about its ecology in the region

• define biologically important areas; that is, areas where aggregations of individuals of a species display biologically important behaviours

• assess the level of concern in relation to different pressures.


1. Marine reptiles of the North-west Marine RegionThe North-west Marine Region is an important area for several species of marine reptiles, including marine turtles and sea snakes.

There are seven species of marine turtles in the world, belonging to two families: the family Cheloniidae, or hard-shelled turtles; and the family Dermochelyidae, which comprises a single species, the leatherback turtle. Six of the seven marine turtle species occur in Australian waters, and all six—the green turtle, hawksbill turtle, loggerhead turtle, flatback turtle, leatherback turtle and olive ridley turtle—occur regularly in the North-west Marine Region. The green, flatback and hawksbill turtles are all listed under the EPBC Act as vulnerable and migratory. The loggerhead, olive ridley and leatherback turtles are listed as endangered and migratory under the Act.

Twenty-nine species of marine snakes have been reported in the region (Guinea 2007a), representing four (of the possible five) lineages of sea snakes, including the family Hydrophiidae or ‘true sea snakes’. Of the 31 species of true sea snakes in Australian waters (Wilson & Swan 2003), 25 species (Attachment 1) are found in the waters of, or adjacent to, the North-west Marine Region (Guinea 2007a). Two of these species (short-nosed seasnake and leaf-scaled seasnake) are listed as critically endangered, and all are listed marine species under section 248 of the EPBC Act.

This report card focuses on the six species of marine turtles and 25 species of true sea snakes known to occur in the North-west Marine Region. These species were selected following consideration of their conservation status; distribution and population structure in the region; life history characteristics; and the potential for the populations in the region to be genetically distinct from populations elsewhere.

Flatback turtle

Flatback turtles (Natator depressus) are endemic to the northern Australian – southern New Guinea continental shelf, extending south in the North-west Marine Region as far as the Muiron Islands (Pendoley Environmental 2005). Flatback turtles eat jellyfish and soft-bodied benthic invertebrates such as sea pens, sea cucumbers, crustaceans, molluscs and soft corals in habitats with unconsolidated substrates. Flatback turtles have been observed foraging on the carbonate banks of the Joseph Bonaparte Gulf and around the pinnacles of the Bonaparte Depression (DEWHA 2007; Donovan et al. 2008). However, little is known about their non-nesting habitat preferences, foraging biology or regional abundance and distribution.


There are two breeding stocks of flatback turtles in the North-west Marine Region. Most of the flatback turtles in the region are part of the North West Shelf breeding stock, while the population that breeds in Cape Domett in the Joseph Bonaparte Gulf forms either a single stock or is part of the western Northern Territory stock (Limpus 2007). Cape Domett and the North West Shelf stocks are two of the largest nesting flatback stocks globally, with annual abundance in the order of several thousand individuals (Pendoley 2005; Whiting et al. 2008).

The North West Shelf stock nests from approximately Exmouth Gulf to the Lacepede Islands and has significant rookeries on Thevenard Island, Barrow Island, the Montebello Islands, Varanus Island, the Lowendal Islands, islands of the Dampier Archipelago, coastal areas around Port Hedland, along much of Eighty Mile Beach, and inshore islands of the Kimberley region where suitable beaches occur. Nesting is also widespread along mainland beaches adjacent to the region such as Mundabullangana. On Barrow Island, flatback turtles breed every two years on average. Nesting begins in late November–December, peaks in January and finishes by February–March. It is estimated that up to thousands of individuals nest on the North West Shelf annually (Pendoley Environmental 2005). Flatback turtles that nest on the Pilbara coast disperse to feeding areas extending from Exmouth Gulf to the Tiwi Islands in the Northern Territory.

Flatback turtles differ from other marine turtles in that they do not have a pelagic phase to their lifecycle. Instead, hatchlings grow to maturity in shallow coastal waters thought to be close to their natal beaches. This may explain why flatback turtles are one of only two species of marine turtles not to have a global distribution (Hamann et al. in press; Walker & Parmenter 1990), although there is evidence that some flatback turtles undertake long-distance migrations between breeding and feeding grounds (Limpus et al. 1983).

Green turtle

Three distinct breeding stocks of green turtles (Chelonia mydas) occur in the region: the North West Shelf stock, the Scott Reef stock and the Ashmore stock (Dethmers et al. 2006).

Green turtles forage for seagrass and algae in estuarine, rocky and coral reef and seagrass habitats. They occasionally feed on macroplankton including jellyfish, dead fish and small crustaceans, as well as mangrove leaves and fruit (Limpus 2008b; Limpus & Chatto 2004). There have been few studies of green turtle feeding areas in the region. Documented sites include Montgomery Reef (Prince 1993), Shark Bay (Environment Australia 2003), the waters surrounding Thevenard Island, possibly over the Barrow Shoals off the south-east coast of Barrow Island, and on the algae-covered rocky intertidal and subtidal platforms off the west coast (Pendoley Environmental 2005). Green turtles also forage around the pinnacles of the


Bonaparte Depression (DEWHA 2007; Donovan et al. 2008). However, based on knowledge about their ecology and habitat use in other parts of Australia, it is likely that green turtles would be found foraging in any seagrass habitat and much of the coral reef habitat that occurs along the Western Australian coast from at least Shark Bay to the northern extent of the North-west Marine Region.

Throughout their lives, adults display a high level of philopatry (a tendency to return to a specific area for different parts of their lifecycle) both to their natal nesting areas and to their feeding areas, irrespective of the distance between them. Tagging studies by Limpus et al. (1992) showed that distances between nesting and feeding areas can range from 2 kilometres to 2600 kilometres. North-west Australian breeding green turtles have ranged as far afield as the Warrior Reef system in central Torres Strait (M Hamann, pers. comm., 2011), parts of the Indonesian archipelago, and south-west Western Australia.

Green turtles are the most common marine turtle breeding in the North-west Marine Region. Green turtles breed extensively throughout the region, and along the coastal (state) areas adjacent to it (Limpus 2008b). Western Australia supports one of the largest remaining green turtle populations in the world, estimated to be in the tens of thousands of adult turtles. Principal near-coastal rookeries include the Lacepede Islands, some islands of the Dampier Archipelago, Barrow Island, the Montebello Islands, and North West Cape and the Muiron Islands. Smaller rookeries adjacent to the Kimberley region include the Maret Islands, Browse Island, Cassini Island and other islands of the Bonaparte Archipelago, and Sandy Islet on Scott Reef. Ashmore Reef is also a significant breeding area for green turtles, providing critical nesting and internesting habitat (Environment Australia 2003), and supporting large and significant feeding aggregations of green turtles.

On Barrow Island the green turtle nesting season begins in November, peaks in January–February and ends in April (Pendoley Environmental 2005). This seasonal profile is likely to be similar for other rookeries for North West Shelf stock. The re-nesting interval for these female green turtles is approximately five years (Hamann et al. 2002). Green turtles nest at Sandy Islet at South Scott Reef year round, with a peak in summer (Smith et al. 2004). Similarly, nesting occurs at Ashmore Reef and Cartier Island year round with a mid-summer peak (DEH 2005).

Hawksbill turtle

Hawksbill turtles (Eretmochelys imbricata) are generally associated with rocky and coral reef habitats, foraging on algae, sponges and soft coral (Pendoley Environmental 2005). Hawksbill turtle feeding grounds are known to occur in the Mary Anne and Great Sandy Island groups to the south of the Barrow Shoals. However, based on what is known about their ecology and habitat use in other parts of Australia, it is likely that hawksbill turtles would be found foraging in any of the coral and/or rocky reef habitat that occurs along the Western Australian coast from at least Shark Bay to the northern extent of the North-west Marine Region.


Hawksbill turtles breed extensively throughout the region and along the coastal (state) areas adjacent to it. There is a single breeding stock in the region: the Western Australian stock, which is centred on the Dampier Archipelago (Limpus 2009a). It is the largest stock in the Indo-Pacific region (Limpus 2002). The most significant breeding areas include Rosemary Island in the Dampier Archipelago, Varanus Island in the Lowendal group, and some islands in the Montebello group. In particular, Rosemary Island supports the most significant hawksbill turtle rookery in the Western Australian region and one of the largest in the Indian Ocean; tens to hundreds of animals nest on the island annually, more than at any other Western Australian rookery (Pendoley Environmental 2005). The hawksbill turtle nesting range extends south from North West Cape to around Coral Bay on the Ningaloo coast. The apparent scarcity of nesting in the Kimberley is due in part to the lack of suitable nesting beaches among the numerous islands. Nesting females dispersing from Pilbara beaches may disperse to Kimberley waters, but this is yet to be confirmed (Pendoley Environmental 2005).

Hawksbill turtles nest in the region all year round with a peak between October and January. Individuals may migrate up to 2400 kilometres between their nesting and foraging grounds. On Rosemary Island, the re-nesting period for hawksbill turtles is generally three years.

Leatherback turtle

Leatherback turtles (Dermochelys coriacea) have the broadest distribution worldwide but are uncommon throughout their Australian range. The leatherback turtle is an oceanic, pelagic species that feeds primarily on jellyfish, sea squirts and other soft-bodied invertebrates at all levels of the water column from the surface to the benthos (Limpus 2009b). It rarely breeds in Australia, although there have been at least two unconfirmed reports of nesting attempts in Western Australia (Limpus 2009b). However, it regularly forages over Australian continental shelf waters. These leatherbacks may have migrated from the larger nesting populations in Indonesia, Papua New Guinea and Solomon Islands, or from populations in the Americas or India (Limpus 2009b).

Loggerhead turtle

Australia has two populations of loggerhead turtle (Caretta caretta)—eastern Australian and western Australian—which are genetically distinct from each other, and from other nesting populations of the Indo-Pacific region (Dutton et al. 2002). Based on annual breeding numbers the western breeding stock is the larger of the two Australian stocks, one of only three stocks in the Indian Ocean (Limpus 2002) and the third or fourth largest stock (of nine) in the world (Conant et al. 2009). Loggerhead turtles occur throughout the North-west Marine Region and forage across a wide range of habitats including rocky and coral reefs, seagrass pastures and estuaries (Limpus & Chatto 2004). Loggerhead turtles are known to forage on the carbonate banks of the Joseph Bonaparte Gulf and around the pinnacles of the Bonaparte Depression


(DEWHA 2007; Donovan et al. 2008), and Shark Bay has critical feeding habitat for loggerhead turtles (Environment Australia 2003). In their pelagic post-hatchling phase loggerheads eat macrozooplankton including medusae, hydrozoans, crustaceans and molluscs (Limpus 1997). In their inshore benthic feeding phase they eat benthic gastropod and bivalve molluscs, crustaceans, echinoderms, jellyfish (Limpus 1997) and anemones (Bjorndal 1997).

In the North-west Marine Region, loggerhead turtles breed principally from Dirk Hartog Island in the south, along the Gnaraloo and Ningaloo coast to North West Cape and the Muiron Islands region in the north, although there have been occasional nesting records from Varanus and Rosemary islands in the Pilbara, and occasional records as far north as Ashmore Reef. The annual nesting population in the region is thought to be several thousand females (Limpus 2008a). Based on current knowledge, all nesting adult loggerhead turtles dispersing from Dirk Hartog Island beaches (near Shark Bay) have remained within Western Australian waters from southern Western Australia to the Kimberley. Turtles dispersing from the North West Cape – Muiron Islands nesting area have ranged north as far as the Java Sea and the north-western Gulf of Carpentaria, and to south-west Western Australia. Dirk Hartog Island in Shark Bay contains the largest breeding rookery for loggerhead turtles in Australia, with up to 1500 females nesting annually on the northern beaches (Baldwin et al. 2003). Hence Dirk Hartog Island has critical nesting and internesting habitats for loggerhead turtles (Environment Australia 2003), and may accommodate up to 75 per cent of the Western Australian breeding population (Prince 1994).

Olive ridley turtle

Olive ridley turtles (Lepidochelys olivacea) are the most abundant marine turtle species breeding globally but the least common in the North-west Marine Region. Their occurrence in the region is presumed to be primarily for foraging purposes. They have been recorded foraging as far south as the Dampier Archipelago – Montebello Islands area, as well as around the pinnacles of the Bonaparte Depression (DEWHA 2007; Donovan et al. 2008). Olive ridley turtles are primarily carnivorous, feeding on gastropod molluscs and small crabs from soft bottom habitats ranging in depth from 6 to 35 metres (Limpus 2008c). Olive ridley turtles may also forage in pelagic waters.

They breed at low densities on Northern Territory beaches outside the North-west Marine Region and no nesting has been reported in Western Australia (Limpus 2008c).


Sea snakes

Sea snakes found in the North-west Marine Region include common species such as the elegant seasnake (Hydrophis elegans) and the ornate seasnake (Hydrophis ornatus), as well as rare species such as the fine-spined seasnake (Hydrophis czeblukovi), and regionally endemic species, such as the Shark Bay seasnake (Aipysurus pooleorum), the brown-lined seasnake (Aipysurus tenuis) and the dusky seasnake (Aipysurus fuscus). Sea snakes in the region occupy three broad habitat types: shallow water coral reef and seagrass habitats, deepwater soft bottom habitats away from reefs, and surface water pelagic habitats (Guinea 2007a).

Information about the species present in the North-west Marine Region comes from field collections (Smith 1926), scientific expeditions (Berry 1986, 1993; Lonnberg & Andersson 1913; Minton & Heatwole 1975) and trawling for fish (Shuntov 1971) and prawns (Ward 1993, 1996). Sea snakes feed on several species of fish including gobies and eels and their eggs. Except for the yellow-bellied seasnake (Pelamis platurus), all species forage over or within benthic habitat (Guinea 2007a). The yellow-bellied seasnake is pelagic and resembles driftwood when motionless, which allows it to prey on small fish that mistakenly seek shelter beneath it. Feeding occurs during the day and snakes are inactive at night. Females are generally larger than males and give birth to their young at sea. Young of most species are born during summer after a 5–7 month gestation. Female sea snakes typically take several years to reach reproductive maturity, have few young, but may breed every year (Heatwole 1997). Species in the North-west Marine Region appear to be resident throughout the year.

The North-west Marine Region contains eight endemic species of sea snake. Five of these species are in the genus Aipysurus and very little is known about them. Two of these, the leaf-scaled seasnake (Aipysurus foliosquama) and the short-nosed seasnake (Aipysurus apraefrontalis), are endemic to the North-west Marine Region and Hibernia Reef, which lies adjacent to the region, 42 kilometres north-east of Ashmore Reef. The small amount of ecological data available indicates that sea snakes have a restricted and patchy distribution and the number of species increases towards the northern parts of the North-west Marine Region.

Areas in the region that are particularly significant for some species include the Sahul Shelf (for short-nosed, leaf-scaled, turtle-headed (Emydocephalus annulatus) and slender-necked (Hydrophis coggeri) sea snakes); Shark Bay (for Shark Bay and elegant sea snakes); the Pilbara coast (for brown-lined and north-western mangrove (Ephalophis greyi) sea snakes); and the Kimberley coast (for brown-lined, Stokes’ (Astrotia stokesii), black-ringed (Hydrelaps darwiniensis) and northern mangrove sea snakes).


Biologically important areas

Biologically important areas are areas that are particularly important for the conservation of the protected species and where aggregations of individuals display biologically important behaviour such as breeding, foraging, resting or migration. The presence of the observed behaviour is assumed to indicate that the habitat required for the behaviour is also present. Biologically important areas have been identified for some EPBC Act listed species found in the North-west Marine Region, using expert scientific knowledge about species’ distribution, abundance and behaviour in the region. The selection of species was informed by the availability of scientific information, the conservation status of listed species and the importance of the region for the species. The range of species for which biologically important areas are identified will continue to expand as reliable spatial and scientific information becomes available.

Biologically important areas for sea snake species have not yet been identified in the North-west Marine Region. It is noteworthy, however, that Ashmore Reef and Cartier Island reserves have been recognised for their high diversity and density of sea snakes. Although recent research has revealed a steep decline in sea snake numbers at Ashmore Reef (Guinea 2007b), at least 13 species were present in the 1990s (Environment Australia 2002).

Biologically important areas have been identified for five species of marine turtle in the region: the hawksbill turtle, loggerhead turtle, flatback turtle, green turtle and olive ridley turtle. Behaviours used to identify biologically important areas for marine turtles include foraging, nesting, internesting and mating.

Biologically important areas are included in the North-west Marine Region Conservation Values Atlas (www.environment.gov.au/cva).

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2. Vulnerabilities and pressures

Vulnerabilities

Marine turtles

The life history patterns of marine turtles, including long life spans and late sexual maturity, make them vulnerable to a range of pressures in the marine environment. Marine turtles spend their life at sea, with females returning to beaches in their natal region to nest as adults (Chaloupka & Limpus 2001; FitzSimmons et al. 1997). While at sea marine turtles are vulnerable to choking and suffocation from marine debris as floating plastics can resemble prey items (Environment Australia 2003).

During the breeding season females are vulnerable to land-based pressures due to limited mobility and, when they return to the sea, may become disoriented by artificial light sources if nesting sites are near industrial and urban areas. Hatchlings are also sensitive to light.

Sea turtles have life history characteristics, physiology and behavioural traits that are heavily influenced by environmental temperature. This is particularly the case during the egg incubation phase (Spotila & Standora 1985) because successful incubation of sea turtle eggs occurs within a narrow thermal range of 25–33 °C (Miller 1985), and all species of marine turtle have temperature-dependent sex determination. Higher nest temperatures may result in a greater number of female hatchlings and reduced hatching success (Feuntes et al. 2009).

The management of marine turtles is difficult because of their complex ecology. The size and status of these populations are difficult to quantify because:

• most of their lives are spent in the marine environment

• hatchlings disperse throughout entire oceans

• individuals follow their own migratory path

• they are migratory, crossing Commonwealth, state and international boundaries

• only the females return to their natal beach, where they lay several clutches of eggs, and not all females nest each year

• they are long lived and slow to mature

• they occupy different habitats at different life stages

• they are subject to a wide range of impacts at different stages of their life.

As a result of the importance of the North-west Marine Region for marine turtles, pressures on marine turtles in the region have the potential to impact on the species of marine turtle that occur elsewhere in Australian and international waters.


Sea snakes

Because sea snakes are slow growing and have few offspring they cannot recover quickly from declines in population size. Large snakes produce more young in a litter than do smaller females that are early in their reproductive lives (Fry et al. 2001). A limited number of benthic species such as eels and gobies comprise the bulk of the diet of most sea snakes in the North-west Marine Region (Fry et al. 2001). This restricted diet increases susceptibility to changes in the trophic structure of the region than for more generalist feeders such as the spine-bellied seasnake (Lapemis curtus) (Fry et al. 2001). Sea snakes are therefore vulnerable both to direct impacts of trawl fishing (bycatch) and to indirect impacts due to habitat destruction and disruption of the trophic structure.

Analysis of pressures

On the basis of current information, pressures have been analysed for the listed marine reptile species discussed in this report card. A summary of the pressure analysis for marine reptiles is provided in Table 1. Only those pressures identified as of concern or of potential concern are discussed in further detail below. An explanation of the pressure analysis process, including the definition of substantial impact used in this analysis, is provided in Part 3 and Section 1.1 of Schedule 1 of the plan.


Table 1: Outputs of the marine reptile species pressure analysis for the North-west Marine Region

Pressure Source

Species

Flatback turtle

Green turtle

Hawksbill turtle

Leatherback turtle

Loggerhead turtle

Olive ridley turtle Sea snakes

Sea level rise Climate change

Changes in sea temperature

Climate change

Ocean acidification Climate change

Changes in terrestrial sand temperature

Climate change

Chemical pollution/ contaminants

Urban development

Agricultural activities

Nutrient pollution Urban development

Agricultural activities

Marine debris Shipping

Vessels (other)

Fishing boats

Land-based activities

Noise pollution Seismic exploration

Onshore and offshore construction

Light pollution Offshore-based activities

Onshore-based activities

Except Cape Domett

Except Ashmore

Physical habitat modification

Dredging

Dredge spoil

Tourism (diving, snorkelling)

Fishing gear (active and derelict)

Onshore/offshore construction

Human presence at sensitive sites

Tourism

Recreational and charter fishing

Research

Except Cape Domett

Except Ashmore

Extraction of living resources

Commercial fishing (domestic)

Extraction of living resources Indigenous harvest

Eggs Eggs and turtles

Eggs and turtles overseas

Bycatch Commercial fishing (domestic)

Oil pollution Shipping

Oil rigs

Collision with vessels

Tourism

Fishing

Invasive species Shipping

Fishing vessels

Land-based activities

Except Ashmore

Legend of concern of potential concern of less concern not of concern data deficient or not assessed


Marine turtles

Changes in sea temperature—climate change

Increasing sea temperature is of potential concern for flatback, green, hawksbill, leatherback, loggerhead and olive ridley turtles. Sea temperatures have warmed by 0.7 ºC between 1910–1929 and 1989–2008, and current projections estimate ocean temperatures will be 1 ºC warmer by 2030 (Lough 2009). Increasing sea temperature has the potential to impact on marine turtles in a number of significant and varied ways, including causing shifts in distribution that may either increase or decrease species range (Davenport 1997; Hawkes et al. 2009; Milton & Lutz 2003), altering life history characteristics (e.g. growth rates, age at maturity and reproductive periodicity) (Balazs & Chaloupka 2004; Chaloupka & Limpus 2001; Fuentes et al. 2010), and reducing prey availability (Chaloupka et al. 2008; Fuentes et al. 2009). However, there is likely to be inter- and intra-species variation. For example, a negative correlation between the slowly increasing mean annual sea temperatures in the core foraging areas for loggerhead turtles, and the trend in the size of annual nesting populations during the following summer in eastern Australia has been identified (Chaloupka et al. 2008). Yet, for green turtles, increased sea temperature could improve seagrass growth, distribution and quality, or alter metabolic rate and growth of individual turtles leading to a positive impact (Hamann et al. 2007). Lack of quantitative data do not allow accurate predictions of impacts; however, rises in sea temperature could have repercussions for all marine turtle species in the region, resulting in a range of effects.

Changes in terrestrial sand temperature—climate change

Increased sand temperature is considered to be of potential concern for flatback, green, hawksbill and loggerhead turtles. Although not strictly linked with sea temperature, another effect of rising global temperatures is the trend towards an increasing female bias in the sex ratio of hatchlings (Fuentes et al. 2009). Actually a result of increasing sand temperature, this temperature-dependent sex determination characteristic is present in all turtle species. It is postulated that this impact may result in the feminising of populations (Fuentes et al. 2009). A rise in sand temperatures may also compromise egg incubation, leading to lower hatchling success and survival of hatchlings (Fuentes et al. 2009). Both changes are concerning given their potential to negatively impact on population viability; however, emerging literature suggests that turtles are responding to these pressures in a highly adaptive manner by, for example, shifting nesting periods to correspond to lower temperatures (Poloczanska et al. 2010). Such a response highlights the difficulties associated with predicting environmental outcomes of climate change and developing effective management responses.


Nutrient pollution—urban development; agricultural activities

Nutrient pollution from urban development and agricultural activities is considered of potential concern for green turtles. Nutrient pollution, known also as eutrophication, refers to an increase in the rate of supply of organic matter—particularly nitrogen, phosphorus and silica—into an ecosystem. These elements are derived from a number of sources including industrial outfalls, aquaculture operations, effluent from vessels and agricultural run-off. Their impacts are mediated by a range of factors including the mixing characteristics of the water, water temperature and available light. Eutrophication is now considered a global threat to coastal marine environments, leading to increased frequency of harmful algal blooms, loss of ecosystem integrity and changes to biodiversity.

Algal blooms have been associated with substandard diets in turtles, which may hamper growth and development, and lead to reduced reproduction (Arthur et al. 2006). It has also been suggested that there is a correlation between pesticide residue and incidences of the fibropapilloma virus, but this has not been proven (Limpus 2008b). Given the expected increase in nutrient pollution associated with the expected growth in industrial and coastal development within the region, this pressure is considered to be of increasing concern to turtle populations.

Marine debris

Marine debris is of concern for flatback, green, hawksbill, leatherback, loggerhead and olive ridley turtles in the region. Marine debris is defined as any persistent, manufactured or processed solid material that has been disposed of, or abandoned, in the marine and coastal environment (UNEP 2005). This includes a range of material from plastics (e.g. bags, bottles, ropes, fibreglass, insulation) to derelict fishing gear and ship-sourced, solid non-biodegradable floating materials (DEWHA 2009).

Marine debris is listed as a key threatening process under the EPBC Act and marine turtles are particularly susceptible to its effects. The internal structure of their throats prevents regurgitation of swallowed items, trapping them in the gut where they decompose, leaking gases into the body cavity that cause the animal to float and ultimately die. White plastic debris (e.g. plastic bags) is of most concern to turtles who mistake it for jellyfish, a key prey item for some species (Derraik 2002). Young turtles are especially vulnerable, possibly because they drift within convergence zones (e.g. rips, fronts and drift lines formed by ocean currents) where high densities of marine debris are known to accumulate. In a recent study by Boyle & Limpus (2008), synthetic materials accounted for up to 46 per cent of total stomach content in green turtle post-hatchlings. Given that hatchlings are not able to compensate for the intake of non-nutritional items, such levels of ingestion of marine debris would result in reduced energy and nitrogen uptake. In addition to the direct impacts of plastic ingestion, research also indicates toxins in the materials are being absorbed by the animals, with unknown, but potentially adverse effects on their demography (Bjorndal et al. 1994).

http://www.ozcoasts.org.au/indicators/sediment_org_matter.jsp


Marine debris data for the region is limited; however, key vectors for the introduction and spread of debris within the system are present. These include high levels of commercial shipping, major current systems (Leeuwin Current and Indonesian Throughflow), active commercial and recreational fisheries, and significant coastal urban development. Despite the paucity of marine debris information for the North-west Marine Region, there are clear indications that debris is having a negative impact on turtles in other parts of the world (Wabnitz & Nichols 2011).

Noise pollution—seismic exploration; offshore and onshore construction activities

Noise pollution is listed as of potential concern to flatback, green, hawksbill, leatherback, loggerhead and olive ridley turtles. There are limited data on the potential impacts of noise pollution to marine turtles. However, industrial development is widespread within the region and noise generated through operations such as seismic surveys and construction (e.g. pile driving, blasting) may adversely impact marine turtles, particularly if these activities occur in areas known to be important for the species and/or during critical life cycle stages (e.g. nesting). Evidence regarding the hearing sensitivities of turtles suggests a hearing range of 250–700 Hz (Weir 2007). Pile driving contains most energy in the low-frequency bandwidth around 1000 Hz or less, depending on pile material, diameter and other properties (Salgado Kent et al. 2009). There have been few studies on the effects of seismic surveys on turtles, although one study indicated turtles exhibit avoidance behaviour when proximate to noise emitted during seismic surveys (McCauley et al. 2000). Noise pollution may induce a startle response and disturb foraging, breeding and migration. Understanding the influence of noise pollution on marine turtles warrants further investigation.

Light pollution—onshore-based activities

Light pollution at or near nesting beaches is of concern for flatback, green, hawksbill and loggerhead turtles. Light pollution is defined as excessive or obtrusive artificial light that is distinct from natural light in five key ways: source, scattering, reflection, directivity and direction (Salmon 2003). Light quality is also an important factor for turtles—white light (containing both short and long wavelengths) repels the animals, while yellow light (composed of a single long wavelength) has no behavioural effects (Salmon 2003). Light pollution along, or adjacent to, nesting beaches poses a particular issue for turtles because it alters critical nocturnal behaviours, particularly the selection of nesting sites and the passage of adult females and emerging hatchlings from the beach to the sea (Limpus 2009a). Consequences of these changes include a decrease in nesting success, beach avoidance by nesting females, and disorientation that leads to increased mortality through predation, vehicles driving on beaches or dehydration (Limpus 2009a; Lorne & Salmon 2007; Witherington & Martin 1996).


Given the particular sensitivity of turtles during nesting, light pollution originating from coastal and industrial development on or near key nesting areas poses a serious threat to turtle populations. Industrial development along the coastal fringe of the North-west Marine Region is extensive and likely to increase. Ongoing investigations are occurring in the region to quantify the impacts of industrial-based lighting on hatchling orientation and dispersal (Pendoley 2005).

Physical habitat modification—dredging/dredge spoil

Physical habitat modification by dredging is of concern for flatback turtles and of potential concern for green, hawksbill, loggerhead and olive ridley turtles. Dredging occurs extensively in state waters and to a lesser extent in the North-west Marine Region. It is projected to become more frequent as port developments and industrial activities expand. The impacts of dredging on marine turtles are twofold: direct mortality of individuals; and indirect mortality arising from habitat modification. Direct mortality is well established in stranding records—turtles killed in this manner have extensive and characteristic injuries (Greenland et al. 2004; Haines & Limpus 2001).

Dredging has the potential to increase sedimentation, reduce water quality and smother benthic habitats. The reduction in suitable benthic habitats may adversely affect marine turtles if the dredged area or sediment spoil ground is in a particularly important foraging area. Dredging also removes existing bottom sediments, leaving smooth channels. Anecdotal reports suggest these channels are used by turtles for resting and may place them in the path of high vessel traffic, thus increasing their exposure to vessel strike injuries (M Hamann, pers. comm., 2011).

Physical habitat modification—fishing gear (active and derelict)

The modification of benthic habitats from bottom trawling is of potential concern for flatback, loggerhead and olive ridley turtles. Trawling impacts on benthic communities are becoming better documented. Data indicate that trawling activities can change the diversity and abundance of fauna as well as potentially change the ecosystem function (Sainsbury et al. 1992; Pitcher et al. 2009). Empirical links between changed benthic habitats and marine turtle diet ecology have not been made but are possible. For example, it is possible that trawl fisheries have influenced benthic communities that correspond with important foraging areas for benthic foraging species (such as flatback, loggerhead and olive ridley turtles) (Moran and Stephenson 2000; Wassenberg et al 2002).


Human presence at sensitive sites—tourism; recreational and charter fishing; research

The presence of humans at sensitive sites is of concern for flatback, green and loggerhead turtles. Marine turtles reside along the region’s coastal zone and breed on numerous sandy beaches adjacent to the region. Marine turtles are particularly sensitive while on shore for nesting and can be easily disturbed by movement and light, hence they are sensitive to people walking or driving along beaches. Clutches of eggs are buried about 50 centimetres deep, and incubating nests and emerging hatchlings can be disturbed by vehicles, camp fires, pets (e.g. dogs), and vehicle and human tracks. The potential impact varies among the species and differs among sites; however, its management warrants precaution.

Extraction of living resources—Indigenous harvest

Indigenous harvest of turtles is of potential concern for flatback, green and hawksbill turtles in the North-west Marine Region. Indigenous harvest of marine turtles has occurred for millennia, the animals being taken for their meat and to make a range of products that includes leather, cosmetics, jewellery and other ornaments (Limpus 2008b). Indigenous harvest continues across the region today under provisions outlined in section 211 of the Native Title Act 1993, which preserves the right of native title holders to continue traditional hunting activities for personal, non-commercial purposes. Adult female green turtles tend to be preferentially taken for meat; eggs of most species are harvested (Limpus 2008b).

There are no data on the levels of marine turtle harvest across northern Australia (Limpus 2008b), but it is likely that marine turtle harvest varies widely across communities and geographic areas adjacent to the region.

Bycatch—commercial fishing

Bycatch from commercial fisheries is of potential concern for flatback, green, hawksbill and loggerhead turtles in the North-west Marine Region. Globally, bycatch is considered to be one of the most significant threats to the survival of turtles (Lewison et al. 2004). Turtles are particularly vulnerable to trawl, gillnet and longline fisheries gear and bycatch interactions typically result in the death of individuals from drowning. All three gear types are used across the North-west Marine Region. Fisheries in which turtles have been recorded as bycatch are the Pilbara Trawl, Exmouth Gulf Prawn and Shark Bay Prawn fisheries. However, since bycatch excluder devices became mandatory for these fisheries, turtle bycatch has reduced (Chaloupka & Limpus 2001; Fletcher & Santoro 2009; Limpus 2007; Limpus 2008b).

Fisheries monitoring programs indicate marked improvement in affected turtle populations over the past decade in eastern Australia since the introduction of mandatory bycatch excluder devices (C Limpus, pers. comm., 2011).


Collision with vessels—tourism; fishing

Collision with tourism and fishing vessels is of potential concern for green, hawksbill and loggerhead turtles. Boat strikes are a common cause of death and injury in marine turtles. Turtles are most vulnerable to boat strike when they are in shallow waters, at the surface basking or coming to the surface to breathe. In the North-west Marine Region there are few quantitative data on mortality of turtles from boat strike, but in the East Marine Region, boat strikes account for a large number of turtle deaths. For example, many tens of green turtle deaths are reported each year in Queensland from boat strike or propellar cuts, but the actual figure is estimated to be in the high tens or low hundreds (Limpus 2008b).

With increasing coastal development in the North-west Marine Region and the associated rise in boating activity, mortality rates in the region are expected to increase in the absence of mitigation measures.

Invasive species

Invasive species are of concern for flatback, green and loggerhead turtles. An invasive species is one occurring beyond its accepted normal distribution, as a result of human activities, and which threatens valued environmental, agricultural or other social resources by the damage it causes. Invasive species adjacent to the North-west Marine Region include foxes and pigs, which pose a significant threat to turtles through egg predation. European red fox and feral pig have both had catastrophic impacts on stocks, particularly the western loggerhead and mainland nesting populations (Limpus & Limpus 2003; Limpus & Parmeter 1985). A fox eradication program by the Western Australian Government and private land-holders has been successful in reducing fox impacts to low levels in some sites (e.g. Ningaloo and Gnaraloo), but uncontrolled egg predation remains an issue, particularly by feral pigs along the northern part of the region.

Sea snakes

Changes in sea temperature—climate change

Changes in sea temperature associated with climate change are of potential concern for sea snakes. Sea temperatures have warmed by 0.7 ºC between 1910–1929 and 1989–2008, and current projections estimate ocean temperatures will be 1 ºC warmer by 2030 (Lough 2009). True sea snakes depend on the water temperature for their body heat (Guinea 1995; Heatwole 1981). Even dark-coloured sea snakes can raise their body temperature by only about 3 °C by basking on the sea surface. Little is known of the thermal requirements and the thermal tolerances of sea snakes and how increased temperatures will affect their behaviour and physiology (Hamann et al. 2007). However, the yellow-bellied seasnake has an upper thermal


tolerance of 36 °C and its distribution has been linked to sea temperature patterns (Dunson & Ehlert 1971). In tropical reef habitats such as Ashmore Reef, surface waters approach its maximum tolerance temperature (36 °C) (Dunson & Ehlert 1971; Graham et al. 1971; Heatwole 1981) and during summer spring tides exceed this maximum for several hours (Guinea 1995). Cooler oceanic water remains a few metres below the surface. These daily thermoclines are predicted to deepen as water bodies warm, and the shallow waters of the North-west Marine Region may become excessively heated throughout the water column. Predicted changes may affect trophic structures and processes and the availability of prey species (Hamann et al. 2007).

Ocean acidification—climate change

The effects of ocean acidification on sea snakes are unknown but are of potential concern. Driven by increasing levels of atmospheric CO2 and subsequent chemical changes in the ocean, acidification is already underway and detectible. Since pre-industrial times, acidification has lowered ocean pH by 0.1 units (Howard et al. 2009). Furthermore, climate models predict this trend will continue with a further 0.2-0.3 unit decline by 2100 (Howard et al. 2009).

The impacts of changes in seawater chemistry include metabolic changes in both adults and young and trophic changes associated with the availability of prey species and suitable habitats, particularly coral reefs. Without further focused research and data accumulation, any predicted changes remain unknown (Hamann et al. 2007).

Physical habitat modification—onshore and offshore construction

Physical habitat modification associated with port construction and maintenance is of potential concern for sea snakes. The North-west Marine Region is under pressure from an expanding and developing oil and gas industry and establishing port facilities for the export of minerals, especially iron ore from the Pilbara. This development requires dredging, pile driving and shoreline modification that have the potential to negatively impact on sea snakes.

No data are available on the impact of these activities on sea snakes in the region. However, a local decrease in sea snake abundance was observed during the construction of extensions to the Broome wharf (Guinea 2007a). Potential impacts to sea snakes from construction activities include physical entrainment in equipment; removal from the area by excessive shock waves from explosions, pile driving and seismic surveys; removal of habitat of prey species; increased turbidity affecting species that rely on vision for feeding; and the covering of foraging habitat with the dredge spoil. Data on sea snakes from elsewhere indicate that once removed from an area, recolonisation takes considerable time and may not occur at all (Burns & Heatwole 1998; Lukoschek et al. 2007).


Bycatch—commercial fishing

Bycatch in commercial fishing activities is of concern for sea snakes. Sea snake bycatch has been recorded in the Northern Prawn Fishery (Ward 2000) (although only a small component of the fishery operates in the North-west Marine Region), the Pilbara Trawl Fishery, the Pilbara Trap Fishery and the Northern Demersal Scalefish Fishery (Penn et al. 2005). Trawling, because of the mesh size of nets, captures more of the larger, more fecund, females (Fry et al. 2001). Being air breathers, sea snakes need to surface at least every 20 minutes when actively foraging. As a consequence, many more survive being captured in trawl nets when the tow time is short, as in the banana prawn fishery. Longer tows—up to three hours in the tiger prawn fishery—may cause increased mortality from drowning.

During the early 1990s, trawlers in the Northern Prawn Fishery were estimated to catch around 100 000 sea snakes each year (Ward 1996; Wassenberg et al. 1994), with 50 per cent of these drowning or being crushed by the weight of the catch (Wassenberg et al. 2001). However, improved gear technology has enabled a reduction in the number of vessels in the fishery without reducing the catch (Milton 2001; Milton et al. 2009). The fishery has developed into a more sustainable industry with reduced pressures on sea snakes through technological innovations in bycatch reduction devices. In 2009, logbook records indicated 7369 sea snakes were caught in the Northern Prawn Fishery (Wilson et al. 2010), although most of this bycatch would occur outside the North-west Marine Region.

Openings in the top of the nets are successful in reducing the incidental capture of sea snakes by 50 per cent (Heales et al. 2008; Milton 2001; Milton et al. 2009). Bycatch reduction devices also reduce the volume of catch in the net and prevent crushing of sea snakes among the catch. Research is continuing into designing and implementing more efficient bycatch reduction devices. Even with these improvements, shallow-water prawn trawling presents the greatest pressure on sea snake populations in the region.

Oil pollution—oil rigs

Oil pollution from oil rigs is of potential concern. Australia has a strong system for regulating industry activity that is the potential source of oil spills and this system has been strengthened further in response to the Montara oil spill. While oil spills are unpredictable events and their likelihood is low based on past experience, their consequences, especially for threatened species at important areas, could be severe. Sea snakes are susceptible to oil on the sea surface (AMSA 2010; Watson et al. 2009). Being air breathers and obligate bottom feeders, oil, its residue and dispersants are either inhaled or ingested (Gagnon 2009). At least two sea snakes were killed in the Montara incident in August–October 2009 (Gagnon 2009; Gagnon & Rawson 2010; Watson et al. 2009). The expansion of oil and gas exploration and extraction in the North-west Marine Region could result in an increased risk of oil spills occurring which may lead to additional pressure on sea snakes in the region.


3. Relevant protection measuresAll six species of marine turtle found in the North-west Marine Region are listed under the EPBC Act as vulnerable or endangered, as well as migratory and marine species. The management of marine turtles is difficult because of their complex ecology. For example, the size and status of marine turtle populations is difficult to quantify because most of their lives are spent in the marine environment; hatchlings disperse throughout entire oceans; individuals follow their own migratory path; they are highly migratory, crossing domestic and international boundaries; only females return to their natal beach to nest; and not all females nest each year. Additionally, they are long-lived and slow to mature, they occupy different habitats at different stages of their life, and are subject to a wide range of impacts at different life stages.

Two species of sea snake are listed as critically endangered (short-nosed seasnake and leaf-scaled seasnake), and all are listed marine species under section 248 of the EPBC Act.

Under the Act it is generally an offence to kill, injure, take, trade, keep or move listed marine, migratory or threatened species on Australian Government land or in Commonwealth waters without a permit.

Alongside the EPBC Act, a broad range of sector-specific management measures to address environmental issues and mitigate impacts apply to activities that take place in Commonwealth marine areas. These measures give effect to regulatory and administrative requirements under Commonwealth and state legislation for activities such as commercial and recreational fishing, oil and gas exploration and production, ports activities and maritime transport. In some instances, as in the case of shipping, these measures also fulfil Australia’s obligations under a number of international conventions for the protection of the marine environment from pollution and environmental harm.

Protection and conservation measures administered under the EPBC Act and relevant to the species described in this report card are listed below.

EPBC Act conservation plans and action plans• Recovery plan for marine turtles in Australia (Environment Australia 2003)

• Threat abatement plan for the impacts of marine debris on vertebrate marine life (DEWHA 2009).

• Threat abatement plan for predation by European red fox (DEWHA 2008)

• Threat abatement plan for predation habitat degradation, competition and disease transmission by feral pigs (DEH 2005)


International measures

Australia is a signatory to the following international agreements for the conservation of marine reptiles:

• Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES)—www.cites.org

• The Bonn Convention: Conservation of Migratory Species (CMS)—www.cms.int• Memorandum of Understanding on the Conservation and Management of Marine Turtles

and Their Habitats of the Indian Ocean and South-East Asia (IOSEA MoU)— www.ioseaturtles.org.

For more information on conservation listings under the EPBC Act and related management objectives and protection measures, visit:

• www.environment.gov.au/coasts/species/marine-species-list.html (listed marine species)

• www.environment.gov.au/epbc/protect/species-communities.html (listed threatened species)

• www.environment.gov.au/epbc/protect/migratory.html (listed migratory species)

• www.environment.gov.au/cgi-bin/sprat/public/sprat.pl (species profile and threats database).


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ATTACHMENT 1: MARINE REPTILE SPECIES OCCURRING IN THE NORTH-WEST MARINE REGION

Table A1: Marine reptile species known to occur in the North-west Marine Region

Species (common name/scientific name) Conservation status

Marine turtles

Flatback turtle (Natator depressus) Vulnerable, migratory, marine

Green turtle (Chelonia mydas) Vulnerable, migratory, marine

Hawksbill turtle (Eretmochelys imbricata) Vulnerable, migratory, marine

Leatherback turtle or leathery turtle (Dermochelys coriacea) Endangered, migratory, marine

Loggerhead turtle (Caretta caretta) Endangered, migratory, marine

Olive ridley turtle or Pacific ridley turtle (Lepidochelys olivacea) Endangered, migratory, marine

Sea snakes

Horned seasnake (Acalyptophis peronii) Marine

Black-ringed seasnake (Hydrelaps darwiniensis) Marine

Brown-lined seasnake (Aipysurus tenuis) Marine

Dubois’ seasnake (Aipysurus duboisii) Marine

Dusky seasnake (Aipysurus fuscus) Marine

Elegant seasnake (Hydrophis elegans) Marine

Fine-spined seasnake (Hydrophis czeblukovi) Marine

Leaf-scaled seasnake (Aipysurus foliosquama) Critically endangered, marine

Northern mangrove seasnake (Parahydrophis mertoni) Marine

North-western mangrove seasnake (Ephalophis greyi) Marine

Olive seasnake (Aipysurus laevis) Marine



Olive-headed seasnake (Disteira major) Marine

Ornate seasnake (Hydrophis ornatus) Marine

Shark Bay seasnake (Aipysurus pooleorum) Marine

Short-nosed seasnake (Aipysurus apraefrontalis) Critically endangered, marine

Slender-necked seasnake (Hydrophis coggeri) Marine

Small-headed seasnake (Hydrophis mcdowelli) Marine

Spectacled seasnake (Disteira kingii) Marine

Spine-bellied seasnake (Lapemis curtus) Marine

Spine-tailed seasnake (Aipysurus eydouxii) Marine

Stokes’ seasnake (Astrotia stokesii) Marine

Turtle-headed seasnake (Emydocephalus annulatus) Marine

Yellow-bellied seasnake (Pelamis platurus) Marine

Table A2: Marine reptile species known to occur in the North-west Marine Region on an infrequent basis


Plain seasnake (Hydrophis inornatus) Marine

Sea snake (Hydrophis ocellatus) Marine

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