La Explotacion Del Inter_Sub_tidal_en_Chile y SudAfrica

8/13/2019 La Explotacion Del Inter_Sub_tidal_en_Chile y SudAfrica

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1 The Exploitation of Intertidal andSubtidal Biotic Resources of Rocky Shores in

Chile and South Africa An OverviewW.R. Siegfried, P.A.R. Hockey, and G.M. Branch

1 1 Introduction

There are few maritime countries in the world whose rocky shores supportsimultaneously well-established, large-scale and successful industries for commerce, recreation and subsistence, based on the natural and man-assistedproduction of intertidal and subtidal algae and invertebrates. Subsistence ex-ploitation stems from at least 100000 years B.P. in South Africa (Thackeray 1988)and from about 10000 years B.P. in Chile (Llagostera 1979), and in both countries large-scale commercial and recreational industries have developed duringthe last 40 years.

On sandy shores in South Africa, small numbers of invertebrates, mainly thesand mussel Donax, are exploited. In contrast, some 35000 t (metric tonnes) ofclams Mesodesma, Venus and Protothaca) and scallops (Pectinidae) are takenannually in Chile, mainly (98 ) for the local market. This accounts for about10 , by mass, of all intertidal and subtidal organisms, excluding fish, takenannually in Chile. Fish are not an important resource in the intertidal subsistenceor commercial industries of either Chile or South Africa, although both countries have large offshore fisheries, and South Africa has a rapidly growing population of recreational shore-anglers. The alga Gracilaria, which grows on softsubstrata, is exploited in both countries, chiefly for export, and in Chile it increasingly is being cultured artificially in sheltered sandy embayments. Commerciallyexploited algae of rocky shores include Lessonia, Ecklonia, Laminaria, Durvil-laea, Iridaea and Gelidium. f importance here is that in both countries, marineorganisms of rocky shores constitute the principal intertidal resource exploitedfor subsistence, recreation and commerce. Moreover, in spite of a marked growthin mariculture in both countries during the last decade o r so (Winter et al. 1984;Cereceda and Wormald 1991; Hecht and Britz 1992), the removal of algae andinvertebrates from the wild remains the backbone of the commercial and subsistence industries.

Here, we provide a brief overview of the scope of the Chilean and SouthAfrican rocky-shore based algae and invertebrate industries, in terms of theirsize, value and prospects. This is preceded by prehistorical and historicalperspectives, providing an introduction to, and platform for, some of the moredetailed treatments contained in subsequent chapters.

W. R. Siegfried (ed.),Rocky Shores: Exploitation in Chile and South Africa Springer-Verlag Berlin Heidelberg 1994


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1 2 Prehistorical nd Historical Exploitation

1.2.1 Spatial Changes in Exploitation

W.R. Siegfried et al.

The widespread occurrence of shellfish in middens in South Africa and Chileindicates that prehistoric exploitation was locally intensive and geographicallyextensive in both countries prior to European colonization. To this day, exploitation remains widespread in Chile, although sections of the coast which are inaccessible serve as important buffer areas from which species can recolonizeadjacent shorelines where they are collected. or example, near-shore islets inChile, protected by their separation from the mainland and by frequent strongwave action, support high densities and a large biomass of the bull kelp Durvil-laea From these islets, recruitment takes place to the nearby m:Hnland where

the kelp is exploited (Castilla and Bustamante 1989 .The spatial pattern of subsistence exploitation in South Africa has changedconsiderably over time in response to demographic changes in human populations. or at least 50000 years, San hunter-gatherers exploited the shores of thewest coast (Volman 1978), although there are prolonged hiatuses in the middens recording their shore-based activities. The third century A.D. saw the arrivalof domestic livestock in the region; whether this signified the arrival of the distinct population of Khoi pastoralists or merely the acquisition of livestock bySan is uncertain. Pastoralists also collected shellfish (Smith 1987 , and, perhaps

due to territorial disputes, it is likely that the adventof

pastoralism affected themobility patterns of the San. Khoi pastoralists and San hunter-gatherers werecertainly present in the area at the time of European colonization, but theirdays were numbered. During the eighteenth century A.D., both the Khoi andSan populations were dramatically reduced by colonial raids and introduced diseases (Elphick 1985; Penn 1987 . Further changes to the San life-style arose asthey became integrated into other cultural groups and were used as a source oflabour in Dutch settlements (Penn 1987 . Within 50 to 100 years of Europeancolonization, the hunter-gatherer life-style of the San ceased to exist on the west

coast, and a once extensive subsistence economy, based to a substantial extenton shellfish, also came to an end. On the southern and eastern Cape coasts, traditional exploitation of the shore has taken place for at least 100000 years (Thackeray 1988 . The subsequent history of pastoralism and persecution by Europeancolonists is similar to that of the west coast, although the hunter-gatherer lifestyle persisted for slightly longer following colonization.

From the Kei River eastwards, the situation was slightly different. Thehunter-gatherers' life-style was impacted by the arrival of agro-pastoralists fromthe north. Whilst the earliest arrivals, in the second and third centuries A.D.,were predominantly agriculturalists, pastoralism played an increasingly important role in their economy with time (Hall 1987 . There are also hiatuses in thearchaeological record of their use of coastal resources, but east-coast subsistencecollectors survived the advent of colonialism, and a modified form of the huntergatherer life-style persists today.

Whereas the behaviour of the east-coast shellfish collectors provides a


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Exploitation Overview 3

valuable window onto the past, changes that have taken place since the early1960s have probably resulted in their having a more severe impact on theshellfish resources than was ever the case previously. The politically motivated

establishment of bantu homelands has resulted in the black African population becoming concentrated, the main coastal concentrations being in Ciskei,Transkei and KwaZulu. The detrimental effects of this shift have beenexacerbated by an accelerating population growth rate.

Even more recently, political changes in South Africa have seen the abolitionof most apartheid laws and the removal of constraints limiting the movementand settlement of people. This has heralded yet another demographic shift, withlarge numbers of people moving from the homelands to the cities. Cape Townhas, for example, almost trebled its population from about 900 000 in 1980 to

an estimated 2.5 million in 1992. Associated with this shift, subsistence exploitation, previously virtually absent from the area since the eradication of the Khoiand San, has intensified locally in the western Cape, and is now influencing thecomposition of intertidal biotas in certain areas. Shores previously dominatedby grazers now are dominated by algae, as a result of the exploitation of limpets(G.M. Branch and R. Bustamante, unpubl. data).

Subsistence exploitation in southern Africa is aimed largely at mussels andlimpets, with smaller amounts of winkles, whelks, octopus and redbait Pyura)being collected. In total, about 35 species are taken in South Africa and some

32 species are exploited in Chile (Jerardino et al. 1992 . Modern commercial ex-ploitation of the intertidal and shallow subtidal zones in South Africa scarcelyoverlaps with subsistence cropping, either spatially or in terms of the targetspecies-a strong contrast with the sit,uation in Chile. Commercial exploitationin South Africa is centred on the southwest and west coasts, the most important species being the west-coast rock'lobster Jasus lalandil), abalone Haliotismidae), two species of kelp Ecklonia maxima and Laminaria pallida), and seaweeds of the genus Gelidium. The potential for commercial exploitation of thelimpets Patella granatina and p argenvillei is currently being explored along

the west coast.Commercial activities are directed at individual, highly profitable species(rather than providing a bulk supply of protein). As a result, the diversityof commercially exploited species is much lower than the diversity of speciesexploited for subsistence. Without exception, the commercially taken speciesare abundant, are relatively easy to collect in bulk, and are collected in largequantities over extensive areas. Commercial collecting rights are concentrated inthe hands of a small number of companies. In all cases the level of exploitationis controlled by rigorous sets of regulations aimed at sustainable utilization,

although the success of such regulations has varied considerably from speciesto species. Subsistence exploitation, by contrast, is extremely difficult to controlby legislation, partly because it involves a large number of people, each operatingat a relatively low and extremely local level.


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1.2.2 Temporal Changes in Exploitation and the Role ofEnvironmental Change

W.R. Siegfried et al.

Shell middens which have accumulated over prolonged periods provide aunique record of changing patterns of exploitation over time. In Chile, one ofthe oldest-known middens, at Punta Curaumilla, dates back to 8500 years B.P.(before present), and indicates two major phases of occupation. The first, in theArchaic, stretches between about 8500 and 4000 years B.P. After a hiatus of 1500years, the second phase of occupation occurred between 2500 and 1300 years B.P.

Despite a substantial period of time elapsing between the two occupations atPunta Curaumilla, the deposits evidence little change in the composition of shellfish species. Five species of chiton, a wide range of keyhole limpets, the loco

Concholepas concholepas, a mussel Perumytilus purpuratus) andan

urchinLoxechinus albus) are the dominant species present in the midden at PuntaCuraumilla. Modern techniques, such as underwater breathing apparatus,which allow more efficient collecting of subtidal organisms, have expanded therange of species that can easily e gathered. or instance, subtidal giant barnacles Austromegabalanus psittiacus), rare in middens, now appear regularly inmarkets. Although there is little change in the species' composition of the PuntaCuraumilla midden over time, changes do occur in the size structure of two of themost abundant of these species, the loco and a keyhole limpet, Fissurella Iimbata.

Oneof

the problems confronting archaeologists isthat

changes in speciescomposition and size structure in middens do not necessarily reflect overexploitation or modification of the behaviour of prehistoric people, but mayresult from changes in environmental conditions (Jerardino, in press). InChile, for example, coastal uplift and EI Nino events can alter the nature ofavailable coastal resources (L1agostera 1979; Castilla 1988). On the southerncoast of South Africa, faunal remains at Nelson Bay also suggest an environmentally induced change in intertidal assemblages. Between about 11 900 and10200 years B.P., the deposits were dominated by a cold-water mussel Choromyt-i us meridionalis); around 9000 years B.P. there was an abrupt switch to a warmwater species Perna perna) (Klein 1972).

On a global scale, changes in sea level will have altered patterns of depositionin middens simply because the coast will periodically have regressed sufficientlyto make it uneconomical for human foragers to carry intertidal organisms to themidden. Temporal changes in the composition of a midden in a cave at Eland'sBay on the west coast of South Africa illustrate the point. During the period50000-] 1 000 years B.P., the late Pleistocene regression would have resulted insea levels falling about 120 m below present, and this site would then have beensituated some 40 m from the coastline, beyond the likely exploitation range ofpeople then occupying the cave. Not surprisingly, the faunal remains depositedin the cave prior to 11 000 years B.P. are dominated by the bones of terrestrialanimals (Klein and Cruz-Uribe 1987 . Subsequently, with the advance of thecoastline closer to the cave, the deposits become swamped by marine remains,including marine mammals, fish and a dense assemblage of molluscs (Parkington


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1981, 1986). More specifically, after 11 000 years B.P. the shellfish deposits aredominated by two species of limpets Patella granatina and P. granularis) whichcomprise >95% of the remains; this situation being maintained for almost 1000

years. Thereafter, mussels Choromytilus meridionalis) and whelks Burnupenaspp.) contribute significantly but variably to the deposits for almost 9000 years(with a hiatus between 7900 and 4350 years B.P.).

One of the more curious features of the Eland's Bay cave is the appearance ofa distinct stratigraphic layer, dated about 9600 years B.P., with dense concentrations of whelks (making up almost 60% of the molluscs). Given that whelks areseldom as abundant as either mussels or limpets, yield less meat and are more difficult to extract from their shells, this apparent change in diet is a puzzle. Avoidance of mussels following incidents of shellfish poisoning caused by toxic red

tides (Horstman 1981) may explain the absence of mussel shells in some lenses,but it does not explain why whelks should be collected in preference to limpets.Between ca. 3000 and 1800 years B.P., rock shelters at Eland's Bay were

scarcely used by humans, and coincident with this, massive open-air middenswere formed immmediately adjacent to rocky platforms in the area. These

mega-middens -up to 30000 m 3 -consist almost entirely of mussels, togetherwith abundant charcoal. Henshilwood et al. (1992) surmise that mega-middensaccumulated at sites where mussels were cooked and dried on the shore, fortransport inland. Mussels are enriched in b13 C compared with terrestrial ani

mals, and Henshilwood et al. (1992) note that human skeletons from the megamidden period are also strongly enriched (Sealy and van der Merwe 1988). Thisimplies that the intake of marine foods was substantial and that transport ofdried mussels may have contributed significantly to the diet, even inland.

Part of the answer to determining whether changes in the species compositionof the Eland's Bay midden over time were due to environmental, rather thananthropogenic, factors may lie in the shells themselves.

One approach to measuring the amount of past environmental change hasbeen to use oxygen isotopes (which reflect the temperature at which shells are

deposited) and carbon isotopes (which may serve as indicators of upwellingperiodicity). The percentage of aragonite in the shell of living representatives ofthe limpet Patella granularis correlates with sea temperature, and a simple andstrong correlation exists between mean sea temperature and the relative widthsof two shell layers in this species (Cohen 1988; Cohen and Branch 1992). Oxygenisotopes ratios for this species and Patella granatina also correlate with mean seatemperature, and carbon-isotope values of P. granatina reflect estimates of localprimary production.

Using shells of known ages from middens on the southwestern African coast,

Cohen et al. (1992) have traced Holocene sea-surface temperatures. They document three periods of 0 isotope enrichment and parallel reductions in thearagonite content of shells. All three correspond to periods of Holocene glacialexpansion: the Younger Dryas 11 000-10000 years B.P.), a neoglacial advance(3000-2000 years B.P.) and the Little Ice Age (ca. 400 years B.P.). The temperature deviations amount to about I-2C lower than present, and their cause


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6 W.R. Siegfried et al.

remains unresolved. One possibility is that interruptions in the production ofAtlantic Deep Water (and, hence, the oceanic conveyer belt ) would have reduced the contribution of warm water from the Agulhas Current into the south

ern Benguela area (Berger and Vincent 1986). Alternatively, lower-than-norma1sea temperatures may reflect increased upwelling induced by an intensificationof atmospheric circulation in the region. Further analyses of shells taken frommiddens on the southeast coast where upwelling is less frequent may resolve theissue.

Differences in the nutrient status of waters washing rocky shores profoundlyinfluence the productivity of intertidal algae and, hence, the growth rates andmaximum sizes of grazers such as limpets (Bosman et al. 1986, 1987; Bosman andHockey 1988a). By analysing isotope ratios in shells from middens and lenses of

known age, it may be possible to derive indices for past changes in the distribution and intensity of upwelling. In time, approaches such as these may help todisentangle the frustrating ambivalence that surrounds present interpretationsof faunal changes in middens (i.e whether they reflect human activities, preferences and rates of exploitation, or are a reflection of environmental change). Thequestion is far from being a distant, academic one; current arguments over thelevels of a sustainable yield for the South African rock lobster revolve aroundthis very issue. The recent slump in the rock lobster industry is caused by a decreased growth rate of the animals. I f slow growth is a manifestation of environ

mental change and is likelyto

be sustained, then the prognosis for a recoveryis

poor, and yields will only be sustainable at a much reduced level of exploitation.On the other hand, the reductions in growth may simply e due to a short-termshortage of food for the rock lobsters, and recovery may then be expected in thenext f w years. The debate is contemporary and non-trivial, potentially involvingmany millions of dollars, but the resolution may well come from developing anunderstanding of historical climate change and its consequences for the marinefauna and flora.

1.2.3 Early uman Impacts on Shellfish Populations

The rates of removal of intertidal organisms by early collectors cannot be quantified from midden remains alone, even though lenses within middens can befairly accurately dated. The proportions of the organisms collected that were deposited in middens is unknown, and the importance of these organisms in thediets of early coastal dwellers fuels a continuing debate (Parkington 1976, 1991;Sealy and van der Merwe 1986; Noli and Avery 1988). Studies of modern exploited intertidal communities show that intensive subsistence exploitation canhave major impacts on both the populations of exploited species and on bioticcommunity structure and functioning. However, there is also evidence that thestability (sensu, Pimm 1984) of some rocky-shore communities is high, with rapidrecovery when exploitation ceases (e.g. Hockey and Bosman 1986; Moreno et al.1986), although this is not always the case (Lambert and Steinke 1986).


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Exploit ation Overview 7

Prehistoric and historical human influences on species populations are mostlikely to be reflected either in a change in relative species abundances or in thesizes of the animals collected. In the face of modern exploitation, these parame

ters can change on temporal scales from hundreds of years to less than a decade(Branch 1975; Siegfried et al. 1985; Hockey 1987).

Excavations at the Punta Curaumilla midden in Chile have documentedchanges in the relative abundance and sizes of several exploited species betweenca. 8800 and 1300 years B P (Ramirez et al. 1991; lerardino et al. 1992). Duringthis period there was a steady decrease in the mean size of locos Concholepasconcholepas from a length of ca. 75 mm to a length of ca. 50 mm. This decreasein size was paralleled, although not to such an extent, by a decrease in the abundance of locos in the midden. The sizes of fissurellid limpets also decreased over

this period, but their abundance increased. At the comparably stratified middenat Eland s Bay, South Africa, the mean size of the limpet Patella granularis decreased by 2 mm over a 10 OOO-year period, and the mean lengths in the lenseswith the smallest and largest limpets differed by only 7 mm (N = 13 lenses). Therewas no comparable change in the sizes of the larger, and generally more abundant, P granatina (Parkington et al. 1992 . At a nearby, recent midden (ca. 650years B.P. , a patchy distribution of limpet sizes and species is apparently consistent with the hypothesis that, over a relatively short time, collectors impactedboth the size structure and relative abundance oflimpet populations (Parkington

et al. 1992).The trophic level or guild to which an exploited species belongs influencesthe confidence that can be placed in ascribing changes in mean size to theactivities of subsistence collectors. In most cases where intraspecific competitionfor food occurs, a reduction in density will lead to an increase in growth rate.This may result in a change in size structure of the population. or example,thinning of limpet populations regularly leads to increased growth rates,coupled with an increased maximum size of individuals. However, patternsthat emerge from manipulating populations of primary consumers through

selective removal can be confounded by environmental influences. The growthrate of limpets is strongly influenced by primary productivity (Bosman andHockey 1988a). Primary productivity in turn is affected by the nutrient regime(Bosman et al. 1986) and also by rock slope (Bosman and Hockey 1988b).Intertidal slope may be altered by the interaction of changing sea level and localtopography. In Chile, such effects may be further exacerbated by tectonic activity(Castilla 1988).

Biological interactions also complicate the effects of exploitation. orexample, locos prey on the filter-feeding mussel Perumytilus purpuratus The

productivityof

such filter-feeders is not linked to the productivityof

epilithicalgae, in contrast to the productivity of grazers. However, reductions in locodensities lead to increased abundances of mussels on the shore, which shouldincrease the growth rate oflocos on the shore. The gradual decrease in the sizes oflocos in the Curaumilla midden (Jerardino et al. 1992 is thus strong evidence that early collectors influenced the size structure and density of animal


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populations. To date, it is probably the best evidence for such effects in eitherChile or South Africa.

The problems and pitfalls inherent in inferring early human impact on

animal populations are magnified when trying to identify effects of exploitation at the community level. Several examples of community-level effects ofmodern exploitation are detailed elsewhere in this volume, but archaeologicalevidence from South Africa and Chile is scant. The early lenses at Eland's Bayare dominated (>90%) by limpets. Approximately 1 000 years ago, mussels andwhelks became increasingly common and, subsequently, the relative importanceof all three groups fluctuated dramatically. Even if one makes the simplifyingassumption that collecting by early exploiters was frequency-dependentto a large degree, and that temporal variations in midden contents reflect

community-level rather than cultural changes, there is still no direct evidenceto support an anthropogenic forcing mechanism over an environmentalone.

The most likely situation in which midden material may provide evidenceof community-level change that can be ascribed to man's activities is when akeystone species (sensu, Paine 1974) is exploited. The potential magnitude of

the effects of such targetted exploitation is well illustrated in the interactionoccurring between Aleutian Island subsistence collectors, sea otters, sea urchinsand seaweeds (Simenstad et al. 1978). Sea otters playa keystone role in regulat

ing subtidal communities in the Aleutian Islands. They remove urchins, resulting in a proliferation of seaweeds due to reduced herbivory. Middens spanning2500 years of aboriginal exploitation indicate that the prey types taken by Aleutsvaried dramatically over time. These dietary changes reflect major differences inthe prey available due to local over-exploitation of sea otters by Aleuts andsubsequent destabilization of the subtidal communities.

None of the species in the Eland's Bay midden can be considered as keystonespecies, sensu stricto. By comparison, the Chilean loco is a keystone species onrocky shores and has been exploited throughout the period of the archaeological

record (Jerardino et al. 1992). In the present-day situation, a reduction in locodensity leads to an increase in intertidal species richness (Castilla and uran1985). A similar increase in species richness was recorded over the 8000 yearstime window of the Punta Curaumilla midden, as locos became smaller and rarer(Jerardino et al. 1992). Whilst this is apparently good circumstantial evidencefor a community-level effect being detectable from archaeological material, theincreased species richness in the more recent deposits of the midden may simplyreflect an increase in the abundance of shells in these lenses, an effect equivalentto a species-area relationship.

The prehistorical and historical exploitation of locos is likely to have had lessof an effect than has modern exploitation. The majority oflocos occur subtidallyand, prior to the advent of diving equipment, this portion of the loco populationwould have had a refuge from human predators and could have acted as a sourcepool for intertidal colonization. On the south and east coasts of South Africa,the ability of the brown mussel erna perna to persist intertidally despite intense


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depredation almost certainly relates in part to the large, unexploited subtidalpopulation (Lasiak and Dye 1989).

There are some instances where recent, intensive exploitation (subsistence and

commercial) has driven exploited populations to very low levels (e.g. Choro-mytilus chorus in Chile; Winter et al. 1984 , or to local extinction (e.g. Patellacandei in the Canary Islands; Hockey 1987 . In the Canary Islands, intensive ex-ploitation of intertidal organisms is considered as one of the factors contributingto the global extinction of the endemic Canarian black oystercatcher Haemato-pus meadewaldoi (Hockey 1987 . There is no evidence, as yet, from Chile, SouthAfrica, or anywhere else in the world that subsistence collection, ancient or modern, has led to the global extinction of any algal or invertebrate species. Severalfactors militate against such extinctions, including prey-switching (frequency

dependent predation) by collectors, the existence of remote stretches of coastor offshore islands which have the potential to act as recruitment sources for ex-ploited shores, and the capacity of many marine species for widespread dispersal.In contrast to terrestrial environments, where there are numerous examples ofman-mediated faunal extinctions, such extinction in marine environments as adirect result of exploitation is rare. The only examples of which we are aware arethe great auk Alca impennis of the north Atlantic, the spectacled cormorant Pha-lacrocorax perspicillatus of the north Pacific and Steller s sea cow Hydrodamalisgigas of the Bering Sea (Greenway 1967; Bertram and Bertram 1973).

Fossil evidence from southern Namibia indicates th t Concho epas conc-holepas once occurred on southern African shores, although t is now restrictedto the coasts of Chile and Peru (Kensley 1985). How widespread Concholepaswas in southern Africa is unknown. Kensley (1985) speculates that the Namibian specimens represent part of a pioneer (founder) population which resultedfrom trans-Atlantic larval drift during the Pleistocene, but did not persist forlong. Similarly, there is fossil evidence for an abundance of large fissurellids onthe northwest coast of South Africa (G.M. Branch, unpubl. data). Large speciesof fissurellids are common on the coasts of Chile and have been throughout

the recorded periodof

subsistence exploitation, but no longer occur in SouthAfrica. Neither locos nor large fissurellids occur in archaeological middens inSouth Africa J. Parkington, pers. comm.). Their extinction from South Africashores was almost certainly environmentally mediated and predated subsistenceexploitation.

1 3 Scope o Modem Exploitation

Accurate and reliable statistics for the take and trade valueof

intertidal andsubtidal resources are difficult, and sometimes impossible, to obtain. There aremany reasons for this, not least the one of secrecy practised by many commercial operators, especially those who operate illegally. Accurate and long-termmonitoring of subsistence takes is non-existent.

The information for the following analysis was obtained from a variety


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Mussels and octopus are heavily exploited along the east coast o SouthAfrica, mainly by anglers for bait. The indirect benefits o these resources aspart o the base o the South African tourist industry, now worth some US 1.5

billion annually, has not been estimated but could be substantial. Recreationalangling and coastal tourism generally are far less developed in Chile.

1.3.4 Prospects for Commercial Exploitation

The South African commercial takes o lobsters and abalone are close to, if notalready at, maximum levels for sustained yields. The exploitation o these organisms is closely managed by governmental agencies.

In recent years, the market value for South African abalone has increasedmuch faster than that for lobsters. Similarly, in Chile the value o C. o -holepas increased relative to that o lobsters and crabs in the 1980s but thecommercial take o this species has decreased drastically as a consequence oover-exploitation and subsequent protective measures enforced by governmental agencies. Significant growth in the trade o any o these animals from the wildin either South Africa or Chile is unlikely in the foreseeable future, and prospectsfor mariculture are not encouraging, except possibly for abalone.

Less than 25% o the South African oyster trade is based on animals taken

from the wild. The bulko

the commercial product (some 5 million table-sizedoysters annually) is cultured artificially, in part from imported spat. The localmarket is near saturation and freight costs make it expensive to export freshwhole oysters. Moreover, there are relatively few places along the South Africancoast that are suitable for the culturing o oysters. In Chile, however, prospectsfor expansion in the trade o oysters are better, and growing steadily. Most(95%) o the total Chilean production (ca. 1000 t) in 1985 was sold on the localmarket. About 25% o this production stems from the cultivation o oysters atsome 30 sites along the coastline. A modern mariculture industry, making use o

the abundanceo

sheltered natural embayments on the southern Chilean coast,could become a major exporter o mussels, clams and oysters to the Atlanticseaboard o South America.

The artificial culturing o mussels has expanded dramatically in recent years,producing thousands o tonnes per annum in both Chile and South Africa. Thesubsistence and recreational takes o mussels along parts o the South Africancoast continue to grow, and exceed levels o sustainable exploitation in somelocalities. Similarly, untenably high subsistence takes o intertidal limpets areoccuring locally but, elsewhere along the South African coast, particularly thewestern seaboard, prospects are fair for a small, but viable, export industry.Chile's intertidal limpets, mainly keyhole limpets Fissurella spp.), are heavilyexploited for subsistence and for export.

Taken together, in both South Africa and Chile, it appears that the prospectsfor significant increases in the takes o all presently commercially valuable intertidal and subtidal invertebrates from rocky shores in the wild are not good.


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Apart from oysters and mussels, mariculture at present promises little for boosting the production of the most valuable animals, with the possible exception ofabalone. The prospects for increasing the take of intertidal and subtidal algae,

in both regions, however, could be quite different.The commercial value of algal products is increasing, and new artificial

methods for anchoring plants are being developed. Both Chile and South Africacould benefit by increasing their algal production, and by refining their algalproducts before exporting them.

Acknowledgements. We are grateful to the Foundation for Research Development and the University of Cape Town Research Committee for financialsupport. We also thank Professor John Parkington and Antonietta Jerardino

for access to unpublished data and for commenting on earlier drafts.

eferences

Berger WH, Vincent E 1986) Sporadic shut-down of North Atlantic deep-water productionduring the glacial-holocene transition. Nature 324:53-55

Bertram GCL, Bertram CK 1973) The modem Sirenia: their distribution and status. Bioi JLinn Soc 5:297-338

Bosman AL, Hockey PAR 1988a) The influence of primary production rate on the populationdynamics of Patella granularis an intertidal limpet. PSZNI Mar EcoI9:181-198Bosman AL, Hockey PAR 1988b) Life-history patterns of populations of the limpet Patella

granularis: the dominant roles of food supply and mortality rate. Oecologia 75:412--419Bosman AL, du Toit IT Hockey PAR, Branch GM 1986) A field experiment demonstrating

the influence of seabird guano on intertidal primary production. Estuarine Coastal Shelf Sci23:283-294

Bosman AL, Hockey PAR, Siegfried WR 1987) The influence of coastal upwelling on thefunctional structure of rocky intertidal communities. Oecologia 73:226 232

Branch GM 1975) Notes on the ecology of Patella concolor and Cellana capensis and theeffects of human consumption on limpet populations. Zool Afr 10:75-85

Castilla JC 1988) Earthquake-caused coastal uplift and its effects on rocky intertidal kelpcommunities. Science 242:440 443

Castilla JC, Bustamante RH 1989) Human exclusion from rocky intertidal of Las Cruces,central Chile: effects on Durvillaea antarctica Phaeophyta, Durvilleales). Mar Ecol ProgSer 50:203-214

Castilla JC, Duran LR 1985) Human exclusion from the rocky intertidal zone of central Chile:the effects on Concholepas concholepas Gastropoda). Oikos 45:391-399

Cereceda LE, Wormald G 1991) Privatization ofthe sea for seaweed production in Chile. NatResour 27:31-37

Cohen AL 1988) Isotopic and mineralogical variation in the shells of Recent marine molluscsfrom the western Cape coast of South Africa. S Afr J Sci 84:917-918

Cohen AL, Branch GM 1992) Environmentally controlled variation in the structure and

mineralogy of Patella granularis shells from the coast of southern Africa: implications forpalaeotemperature assessments. Palaeogeogr Palaeoclimatol Palaeoecol 91 :49-57Cohen AL, Parkington JE, Brundrit GB, van de Merwe NJ 1992) A Holocene sea surface

temperature record in the mollusc shells from the southwest African coast. Quat Res 38:123-131

Duran LR, Castilla JC, Oliva D 1987) Human predation intensity on rocky shores at LasCruces, central Chile. Environ Conserv 14:143-149


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Elphick R 1985) Khoikhoi and the founding of white South Africa. Raven Press, Johannesburg

Greenway JC 1967) Extinct and vanishing birds of the world. Dover Publications, New YorkHall M 1987) The changing past: farmers, kings and traders in southern Africa, 200--1860.

David Philip, Cape TownHecht T, Britz PJ 1992) The current status, future prospects and environmental implications

ofmar iculture in South Africa. S Afr J Sci 88:335-342Henshilwood C, Nilssen P, Parkington J Mussel drying and food storage in the late Holocene,

SW Cape, South Africa. J Field Archaeol in press)Hockey PAR 1987) The influence of coastal utilization by man on the presumed extinction

of the Canarian black oystercatcher Haematopus meadewaldoi Bannerman. Bioi Conserv39:49-62

Hockey PAR, Bosman L 1986) Man as an intertidal predator in Transkei: disturbance, community convergence and management of a natural food resource. Oikos 46:3-14

Hockey PAR, Bosman AL, Siegfried WR 1988) Patterns and correlates of shellfish exploita

tion by coastal people in Transkei:an

enigmaof

protein production. J Appl EcoI25:353-363Horstman D 1981) Reported red tide outbreaks and their effect on fauna of the west andsouth coasts of South Africa, 1959-1980. Fish Bull S Afr 15: 71-88

Jerardino A Mid to late Holocene sea level fluctuations: the archaeological evidence at TortoiseCave, south western Cape, South Africa. S Afr J Sci in press)

Jerardino A, Castilla JC, Ramirez JM, Hermosilla N 1992) Early coastal subsistence patterns in central Chile: a systematic study of the marine invertebrate fauna fron the site ofCuraumilla-l. Lat Am Antiquity 3:43-62

Kensley B 1985) The fossil occurrence in southern Africa of the South American intertidalmollusc Concholepas concholepas Ann S Afr Mus 97:1-7

Klein R G 1972) Preliminary report on the July through September 1970 excavations at NelsonBay Cave, Plettenberg Bay Cape Province, South Africa). Palaeoecol Af6:177-208

Klein RG, Crutz-Uribe K 1987) Large mammal and tortoise bones from Elands Bay Caveand nearby sites, Western Cape Province, South Africa. In: Parkington JE, Hall M eds)Papers in the prehistory of the western Cape, South Africa. BAR International Series 332 ii)Oxford University Press, Oxford, pp 132-163

Lambert G, Steinke TD 1986) Effect of destroyingjuxtaposed mussel-dominated and corallinealgal communities at Umdoni Park, Natal coast, South Africa. S Afr J Mar Sci 4:203-217

Lasiak T, Dye A 1989) The ecology of the brown mussel Perna Perna in Transkei, southern Africa: implications for the management of a traditional food resource. Bioi Conserv47:245-257

L1agostera A 1979) 9,700 Years of maritime subsistence on the Pacific: an analysis by meansof bioindicators in the north of Chile. Am Antiquity 44:309-324

Moreno CA, Lunecke KM, LepezMI

1986) The responseof an

intertidal Concholepas conc-holepas Gastropoda) population to protection from man in southern Chile and the effectson benthic sessile assemblages. Oikos 46:359-364

Noli D, Avery G 1988) Protein poisoning and coastal subsistence. J Archaeol Sci 15:395-401Paine RT 1974) Intertidal community structure: experimental studies on the relationship be

tween a dominant competitor and its principal predator. Oecologia 15:93-120Parkington J 1976) Coastal settlement between the mouths of the Berg and Olifants Rivers,

Cape Province. S Afr Archaeol Bull 31:127-140Parkington J 1981) The effects of environmental change on the scheduling of visits to Elands

Bay cave, Cape Province, South Africa. In: Hodder I Isaac G, Hammond N eds) Patternsof the past. Cambridge University Press, Cambridge pp 341-359

Parkington J 1986) Landscape and subsistence changes since the Last Glacial Maximumalong the western Cape coast. In: Strauss LG ed) The end of the Palaeolithic in the NewWorld. Br Archaeol Rep 284:201-227

Parkington JE 1991) Approaches to dietary reconstruction in the western Cape: are you whatyou have eaten? J Archaeol Sci 18:331-342

Parkington JE, Yates R, Manhire A, Halkett D 1986) The social impact of pastoralism in thesouthwestern Cape. J Anthropol ArchaeoI5:313-329


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Exploitation Overview S

Parkington JE, Nilssen P, Reeler C Henshilwood C 1992) Making sense of space at Dunefieldmidden campsite, western Cape, South Africa. S Afr Field Archaeoll:63-71

Penn NG 1987) The frontier in the western Cape, 1700-1740. In: ParkingtonJE Hall M eds)Papers in the prehistory of the western Cape, South Africa. BAR International Series 332 ii).Oxford University Press, Oxford, pp 462-S03

Pimm SL 1984) The complexity and stability of ecosystems. Nature 307:321-326Ramirez JM, Hermosilla N, Jerardino A, Castilla JC 1991) Analisis bio-arqueologico prelim

inar de un sitio de cazadores recolectores costeros: Punta CuraumilJa-l, Valparaiso. Actasdel XI Congreso Naciomil de Arqueologia Chilena, vol III. Museo Nacional de HistoriaNatural, Sociedad Chilena de Arqueologia, Santiago, Chile, pp 81-93

Sealy JC, van der Merwe NJ 1986) Isotope assessment and the seasonal-mobility hypothesisin the south-western Cape of South Africa. Curr AnthropoI27:13S-ISO

Sealy J C , van der Merwe NJ 1988) Social, spatial and chronological patterning in marine fooduse as determined by 6 13 C measurements of Holocene human skeletons from the southwestern Cape, South Africa. World Archaeol20 87-102

Siegfried WR Hockey PAR, Crowe AA 198S) Exploitation and conservation of brown musselstocks by coastal people of Transkei. Environ Conserv 12:303-307Simenstad CA, Estes JA, Kenyon WK 1978) Aleuts, sea otte rs and alternate stable-state com

munities. Science 200:403-411Smith AB 1987) Seasonal exploitation of resources on the Vredenburg peninsula after 2000

B.P. In: Parkington JE, Hall M eds) Papers in the prehistory of the western Cape, SouthAfrica. BAR International Series 332 ii) Oxford University Press, Oxford, pp 393-402

Thackeray JF 1988) Molluscan fauna from Klasies River, South Mrica. S M r Archaeol Bull43:27-32

Volman TP 1978) Early archaeological evidence for shellfish collecting. Science 201:911-913Winter JE, Toro JE, Navarro JM, Valenzuela GS, Chapparo OR 1984) Recent developments,

status and prospects of molluscan aquaculture on the Pacific coas t of South America. Aquaculture 39:95-134

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