Impacts of Shellfish Aquaculture on the Environment
Total Page：16
File Type：pdf, Size：1020Kb
Shellfish Industry Development Strategy A Case for Considering MSC Certification for Shellfish Cultivation Operations April 2008 CONTENTS Page Executive Summary 3 Introduction 5 Mollusc Cultivation Mussel Cultivation Bottom Culture 6 Spat Collection 6 Harvesting 7 Suspended Culture 7 Longline Culture 8 Pole Culture 8 Raft Culture 9 Spat Collection 10 Environmental Impacts 11 Scallop Cultivation Japanese Method 13 New Zealand Methods 15 Scottish Methods 15 Environmental Impacts 16 Abalone Cultivation 16 Hatchery Production 17 Sea Culture 17 Diet 18 Environmental Impacts 19 Clam Cultivation 19 Seed Procurement 20 Manila Clams 20 Blood Cockles 20 Razor Clams 21 Siting of Grow Out Plots 21 Environmental Impacts 21 Oyster Cultivation 23 Flat Oysters 24 Cupped Oysters 24 Hanging Culture 24 Raft Culture 24 Longline Culture 25 Rock Culture 25 Stake Culture 25 Trestle Culture 25 Stick Culture 26 1 Ground Culture 26 Environmental Impacts 27 Crustacean Culture Clawed Lobsters Broodstock 29 Spawning 29 Hatching 29 Larval Culture 30 Nursery Culture 30 On-Growing 31 Ranching 31 Environmental Impacts 32 Spiny Lobsters 32 Broodstock and Spawning 33 Larval Culture 33 On-Growing 33 Environmental Impacts 34 Crab Cultivation Broodstock and Larvae 34 Nursery Culture 35 On-growing 35 Soft Shell Crab Production 36 Environmental Impacts 36 Conclusions 37 Acknowledgements 40 References 40 2 EXECUTIVE SUMMARY The current trend within the seafood industry is a focus on traceability and sustainability with consumers and retailers becoming more concerned about the over-exploitation of our oceans. The Marine Stewardship Council (MSC) has a sustainability certification scheme for wild capture fisheries. Currently there is no certification scheme for products from enhanced fisheries1 and aquaculture2. It is the view of many producers that the production of shellfish in enhanced fisheries and aquaculture is more sustainable than the wild capture fisheries for these products and that certification for these products should be considered. The purpose of this report was to review the current scientific literature and compare the results to the criteria required for compliance to Principle 2 of the MSC s Principles and Criteria for Sustainable Fishing in order to determine whether such enhanced shellfisheries could proceed through MSC assessment. Shellfish production can be divided into mollusc cultivation and crustacean cultivation. Mollusc cultivation mainly concerns bivalve molluscs such as mussels, oysters and scallops. For example mussel culture takes place on the seabed or in suspension from rafts and longlines. Bottom culture is characterised by the re-laying of wild harvested spat onto subtidal and intertidal beds. The mussels are grown for 1-2½ years before harvesting by either hand-collection, hand-raking or hydraulic dredge. Hand-collection and hand-raking support artisanal fisheries and have little impact on the environment, and as such may comply with the criteria for Principle 2. The use of hydraulic dredges has a greater impact on the environment which may prove too detrimental to allow compliance to Principle 2. For a definitive conclusion to be made research into this specific area should be conducted. The main issue with suspended culture concerns the increase in sedimentation below farm systems and the effect sedimentation has on the ecosystem. In the context of this report, sedimentation refers to the settlement of organic and inorganic particulate matter settling from the water onto the seabed. There are conflicting arguments within the literature; however the majority of research indicates that impacts are minimal and localised. It is possible to show that suspended culture could comply with Principle 2. Scallop cultivation is similar to mussel culture in that it can be divided into suspended culture or bottom culture, although bottom culture is classified as stock enhancement due to the mobile nature of scallops. Suspended culture has the same potential impacts of mussel culture with sedimentation being the primary concern. There has been much less research into the cultivation of scallops but the current research suggests that there are no adverse impacts on the environment. The restocking of scallops has a more detrimental impact on the environment due to the harvesting method by dry dredge (scallop dredge), which is a high- impact gear which could be destructive if used in sensitive areas. The environmental impacts of abalone culture have received little if any attention from the scientific community and as such no conclusion regarding compliance to Principle 2 could be made. It is noted that there may be issues with the use of wild harvested algae as a food source for the abalone. Clam culture generally takes place in or on the seabed. As with other bottom cultures, the use of dredging to harvest the product could raise concerns regarding the environmental impacts of this activity if used in sensitive areas. More research is required in this area as the conclusions often have to be inferred from wild capture fisheries which impact much larger 1 An enhanced fishery is described as a wild capture fishery where the natural population is enhanced through the input of hatchery reared juveniles or the introduction of structures to enhance production. 2 Aquaculture can be defined in many ways; for the purpose of this report aquaculture is defined as the controlled farming of aquatic organisms from the larval stage to commercial size. 3 areas. There are also examples of clams being grown in bags placed on trestles. This method has a reduced impact and may comply with the criteria for Principle 2. Oyster cultivation is possibly one of the most sustainable types of shellfish culture. There are a wide range of methods for culturing oysters, mainly concerned with the use of a structure to support the growth of the oysters either in suspended culture or on the seabed. Concerns have been raised regarding the removal of large quantities of phytoplankton (Chapelle et al, 2000; Newell, 2004) and the increase in sedimentation, however, as with mussel culture there are conflicting arguments within the literature and it appears that local conditions have an important influence on the extent of impacts from culture systems. The major concern with oyster culture in the USA is the use of Carbaryl, a pesticide, to control burrowing shrimp populations. By removing organisms from the ecosystem such a practice could result in a failure to meet the criteria of Principle 2. In contrast to mollusc culture, the culture of crabs and lobsters is in its infancy. Lobster culture is mainly concerned with taking wild broodstock and rearing larvae to a stage where survival rates are higher than in the wild, at which point the juvenile lobsters are re- introduced into the natural environment. The use of local broodstock and selective harvesting methods of the fishery could meet the criteria for Principle 2. Providing the natural population is not over exploited and healthy, the restocking exercises can improve the wild stocks. Spiny lobsters have received more attention in the tropics and the concerns with their culture are the low numbers of available larvae from wild stocks. Crab culture is confined to the tropics where the current trend is to integrate the culture with mangrove regeneration. Integrated cultivation methods of this kind are improving the environment and could provide a good example to the rest of the aquaculture industry. The concerns over crab culture are the use of wild caught larvae for on-growing and the use of by- catch as a food source. At present the industry is perceived as small and sustainable and would likely meet the criteria for Principle 2, but to support a growth of the industry hatchery production of larvae and artificial feeds will need to be developed. In conclusion, it appears that local conditions are vitally important as to whether the impacts from shellfish aquaculture are having a detrimental effect. A principle that should be considered when assessing the sustainability of a product is the carrying capacity of the culture site. In particular interest of environmental sustainability is the ecological carrying capacity, which is the level of production that an area can support without having a negative impact on the environment. The carrying capacity can be assessed using models and it is suggested that these models are used for each site when considering whether a product is sustainable. It should also be noted that shellfish culture can have positive effects on the environment by filtering the water column and removing excess nutrients and increasing benthic-pelagic coupling (Newell, 1988; Mann, 2000) and that this should be considered, and written into the criteria for principles of sustainability, as it is an important factor that wild capture fisheries cannot offer. Enhanced shellfisheries should be considered as suitable for proceeding through MSC assessment as though a wild-caught fishery as they operate quite differently from traditional finfish aquaculture systems. 4 INTRODUCTION The shellfish industry relies on a complex relationship between producer, retailer and consumer. At present there is a lot of focus from the consumer on traceability, with sustainability of the product being a focal point of this traceability. The demand from the consumer for sustainable produce has led to retailers to search for such products. Sustainable accreditation is currently administered by the Marine Stewardship Council (MSC), who determines whether a fishery is managed effectively and fished in a sustainable manner. Currently, the MSC only certifies un-enhanced wild capture fisheries, but with more focus being placed on certified products, there is a call for certification of enhanced fisheries and aquaculture products from some of the larger retailers (http://www.msc.org/html/ni_346.htm). The purpose of this report is to examine the methods used to culture shellfish, or enhance their fisheries, and by reviewing the current scientific research illustrate; any environmental impacts which may prevent the sustainability of the activity, the gaps in the research, and whether there is scope for these products to be certified by the MSC.