Issues in Ecology Number 8 Winter 2001 to die on the beach.Thus the capture of the 1.7 billion wild Introduction of Non-Native Fish and Pathogens fry stocked annually in Philippine milkfish ponds results in destruction of more than 10 billion fry of other finfish spe- Aquaculture can also affect stocks of wild fish by cies.In India and Bangladesh,up to 160 fish and shrimp fry allowing escapes of non-native species and by spreading dis are discarded for every fry of giant tiger shrimp collected to eases among both farmed and wild fish.Scientists call these stock shrimp ponds. The magnitude of annual fry bycatch introductions of non-native organisms biological pollution. has been estimated at somewhere between62 millon and Atlantic salmon-the dominant salmon species 2.6 billion in three collecting centers in West Bengal.India. farmed worldwide-frequently escape from net pens. some areas of the North Atlantic Ocean,as much as 40 Changes in Ocean Food Webs In the Nohrter more than a qua Stocks of som nd the fish ave reportedly escaped sinc 1980 and At on by ves. Washington toA g ev 9 tors such as codand genetic n p the cline. In the North Sea fo many capelin sandeel.and N This fo man ndar rod lation s of wild Atlar In the Pacific Nort west there is evidence that escaped At. lantic salmon now breed in some streams populations sizes,and reproductive success of various seal ing for spawning sites with beleaquered wild Pacific salmor and seabird colonies.Similarly,off the coast of Peru,scien- Movement of captive fish stocks for aquaculture tists have documented a strong interaction between ancho- purposes can also increase the risk of spreading pathogens veta stocks and the size of sea bird and mammal populations. The relationships between farmed and wild fish and disease Figure-Ecological links gro feed between intensive fish and u 01 aquati bas of seafood. blue efo p duction fish maal red lines indicate negativ feedbacks.(Modified from Naylor et al.2000) Fish or shrmp pond 7 Issues in Ecology Number 8 Winter 2001 to die on the beach. Thus the capture of the 1.7 billion wild fry stocked annually in Philippine milkfish ponds results in destruction of more than 10 billion fry of other finfish spe￾cies. In India and Bangladesh, up to 160 fish and shrimp fry are discarded for every fry of giant tiger shrimp collected to stock shrimp ponds. The magnitude of annual fry bycatch has been estimated at somewhere between 62 million and 2.6 billion in three collecting centers in West Bengal, India. Changes in Ocean Food Webs Stocks of some small ocean fish exploited for fish meal are over-fished, and their populations fluctuate sharply during the climate shifts brought on by El Nino-Southern Oscillation events. In seasons when these stocks are depleted, available food supplies for commercially valuable marine preda￾tors such as cod and also marine mammals and seabirds de￾cline. In the North Sea, for example, over-exploitation of many capelin, sandeel, and Norway pout stocks, largely for production of fishmeal, has been linked to declines of other wild fish such as cod and also changes in the distribution, populations sizes, and reproductive success of various seal and seabird colonies. Similarly, off the coast of Peru, scien￾tists have documented a strong interaction between ancho￾veta stocks and the size of sea bird and mammal populations. Introduction of Non-Native Fish and Pathogens Aquaculture can also affect stocks of wild fish by allowing escapes of non-native species and by spreading dis￾eases among both farmed and wild fish. Scientists call these introductions of non-native organisms “biological pollution.” Atlantic salmon — the dominant salmon species farmed worldwide — frequently escape from net pens. In some areas of the North Atlantic Ocean, as much as 40 percent of Atlantic salmon caught by fishermen is of farmed origin. In the North Pacific Ocean, more than a quarter million Atlantic salmon have reportedly escaped since the early 1980s, and Atlantic salmon are regularly caught by fishing vessels from Washington to Alaska. Increasing evidence sug￾gests that farm escapees may hybridize with and alter the genetic makeup of wild populations of Atlantic salmon, which are genetically adapted to their natal spawning grounds. This type of genetic pollution could exacerbate the decline in many locally endangered populations of wild Atlantic salmon. In the Pacific Northwest, there is evidence that escaped At￾lantic salmon now breed in some streams, perhaps compet￾ing for spawning sites with beleaguered wild Pacific salmon. Movement of captive fish stocks for aquaculture purposes can also increase the risk of spreading pathogens. The relationships between farmed and wild fish and disease Figure 6 — Ecological links between intensive fish and shrimp aquaculture and cap￾ture fisheries. Thick blue lines refer to main flows from aquatic production base through fisheries and aquac￾ulture to human consump￾tion of seafood. Thin blue lines refer to other inputs needed for production (e.g., agro feed, fish meal, seedstock, etc.). Hatched red lines indicate negative feedbacks. (Modified from Naylor et al. 2000)