26238Impacts of Shellfish Aquaculture on the Environment

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    April 2008

    Shellfish Industry Development StrategyA Case for Considering MSC Certification for ShellfishCultivation Operations

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    CONTENTS

    Page

    Executive Summary 3

    Introduction 5

    Mollusc Cultivation

    MusselCultivationBottom Culture 6

    Spat Collection 6Harvesting 7

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

    ScallopCultivationJapanese Method 13New Zealand Methods 15Scottish Methods 15Environmental Impacts 16

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

    Clam Cultivation 19Seed Procurement 20ManilaClams 20Blood Cockles 20Razor Clams 21

    Siting of Grow Out Plots 21Environmental Impacts 21

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

    Trestle Culture 25Stick Culture 26

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    Ground Culture 26Environmental Impacts 27

    Crustacean Culture

    Clawed Lobsters

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

    Spiny Lobsters 32Broodstockand Spawning 33

    Larval Culture 33On-Growing 33Environmental Impacts 34

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

    Conclusions 37

    Acknowledgements 40

    References 40

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    EXECUTIVE SUMMARY

    The current trend within the seafood industry is a focus on traceability and sustainability withconsumers and retailers becoming more concerned about the over-exploitation of our oceans.The Marine Stewardship Council (MSC) has a sustainability certification scheme for wild

    capture fisheries. Currently there is no certification scheme for products from enhancedfisheries1 and aquaculture2. It is the view ofmany producers that the production of shellfishin enhanced fisheries and aquaculture is more sustainable than the wild capture fisheries forthese products and that certification for these products should be considered. The purpose ofthis report was to review the current scientific literature and compare the results to the criteria

    required for compliance to Principle 2 of the MSC s Principles and Criteria for SustainableFishing in order to determine whether such enhanced shellfisheries could proceed throughMSC assessment.

    Shellfish production can be divided into mollusc cultivation and crustacean cultivation.Mollusc cultivation mainly concerns bivalve molluscs such as mussels, oysters and scallops.For example mussel culture takes place on the seabed or in suspension from rafts and

    longlines. Bottom culture is characterised by the re-laying of wild harvested spat ontosubtidal and intertidal beds. The mussels are grown for 1-2 years before harvesting byeither hand-collection, hand-raking or hydraulic dredge. Hand-collection and hand-rakingsupport artisanal fisheries and have little impact on the environment, and as such may complywith the criteria for Principle 2. The use of hydraulic dredges has a greater impact on theenvironment which may prove too detrimental to allow compliance to Principle 2. For adefinitive conclusion to be made research into this specific area should be conducted. Themain issue with suspended culture concerns the increase in sedimentation below farm systems

    and the effect sedimentation has on the ecosystem. In the context of this report,sedimentation refers to the settlement of organic and inorganic particulate matter settling from

    the water onto the seabed. There are conflicting arguments within the literature;however themajority of research indicates that impacts are minimal and localised. It is possible to showthat suspended culture could comply with Principle 2.

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

    The environmental impacts of abalone culture have received little if any attention from thescientific community and as such no conclusion regarding compliance to Principle2 could bemade. It is noted that there may be issues with the use of wild harvested algae as a foodsource for the abalone.

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

    1An enhanced fishery is described as a wild capture fishery where the natural population is enhanced

    through the input of hatchery reared juveniles or the introduction of structures to enhance production. 2Aquaculture can be defined in many ways; for the purpose of this report aquaculture is defined as thecontrolled farming of aquatic organisms from the larval stage to commercial size.

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    areas. There are also examples of clams being grown in bags placed on trestles. This method

    has a reduced impact and may comply with the criteria for Principle 2.

    Oyster cultivation is possibly one of the most sustainable types of shellfish culture. There area wide range of methods for culturing oysters, mainly concerned with the use of a structure tosupport the growth of the oysters either in suspended culture or on the seabed. Concerns have

    been raised regarding the removal of large quantities of phytoplankton (Chapelle et al, 2000;Newell, 2004) and the increase in sedimentation, however, as with mussel culture there areconflicting arguments within the literature and it appears that local conditions have animportant influence on the extent of impacts from culture systems. The major concern withoyster culture in the USA is the use of Carbaryl, a pesticide, to control burrowing shrimppopulations. By removing organisms from the ecosystem such a practice could result in afailure to meet the criteria of Principle 2.

    In contrast to mollusc culture, the culture of crabs and lobsters is in its infancy. Lobsterculture is mainly concerned with taking wild broodstock and rearing larvae to a stage wheresurvival rates are higher than in the wild, at which point the juvenile lobsters are re-

    introduced into the natural environment. The use of local broodstock and selective harvestingmethods of the fishery could meet the criteria for Principle 2. Providing the naturalpopulation is not over exploited and healthy, the restocking exercises can improve the wildstocks. Spiny lobsters have received more attention in the tropics and the concerns with theirculture are the low numbers of available larvae from wild stocks.

    Crab culture is confined to the tropics where the current trend is to integrate the culture withmangrove regeneration. Integrated cultivation methods of this kind are improving theenvironment and could provide a good example to the rest of the aquaculture industry. Theconcerns over crab culture are the use of wild caught larvae for on -growing and the use of by-catch as a food source. At present the industry is perceived as small and sustainable andwould likely meet the criteria for Principle2, but to support a growth of the industry hatchery

    production of larvae and artificial feeds will need to be developed.

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

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

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    INTRODUCTION

    The shellfish industry relies on a complex relationship between produ

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