http://www.canada.com/edmonton/edmontonjou...a6-83b9371ff55d
QUOTE
Cod's absence changes marine life
Ecological disaster boon for fishers: report
Margaret Munro
CanWest News Service
Friday, June 10, 2005
Overfishing has so profoundly altered Canada's East Coast ecosystem it is an open question whether the cod will ever return, says a study on the demise of one of the world's greatest fisheries.
Small fish and bottom-feeders, such as crab and shrimp, have flourished in the cod's absence and appear to have a "lock on the system" that is preventing recovery, says Kenneth Frank, a senior scientist with the federal Fisheries Department. He is the lead author of the report published today in the journal Science.
The study details how the decimation of cod stocks in the 1990s has had a domino effect which radically restructured the marine food web. This is the first time such a "trophic cascade" has been documented in an open-ocean ecosystem.
Cod was for centuries the most abundant predator in the East Coast marine ecosystem and supported a thriving fishery. The stocks, which were still plentiful in the early 1980s, crashed a few years later and a moratorium was placed on cod fishing in 1993.
Fish managers and fishing communities hoped the cod would bounce back if nets were kept out of the water for a few years. But 12 years into the moratorium, the cod show no sign of recovery and key stocks are listed as endangered and threatened.
Frank and his colleagues at the Bedford Institute of Oceanography and Queen's University doubt there will be a recovery any time soon, given the "new fishery regime" which has evolved in the cod's absence. The best hope, says Frank, is to set up a network of marine protected areas to aid recovery.
Frank and his colleagues combed through 40 years worth of data showing changes reverberating across the food web as the cod disappeared from prime fishing grounds on the eastern Scotian Shelf off Nova Scotia. Frank says there is evidence the same kind of domino effect hit the Grand Banks, Gulf of Labrador and Labrador Shelf.
Snow crab, shrimp and small fish, such as herring, capelin and sand lance flourished on the Scotian Shelf in the absence of the predatory cod. The seal population boomed as the animals feasted on the abundant smaller species. Insect-like zooplankton dropped by as much as 45 per cent because the proliferating crab, shrimp and small fish gobble them up. This in turn boosted levels of plankton, which were no longer grazed on as heavily by zooplankton. And the nitrate level in seawater dropped as the flourishing plankton sucked up more of the nutrient.
The scientists say the restructuring likely explains why the cod-fishing moratorium, which has been coupled with improved environmental conditions, has failed to bring back the cod. Some observers had linked a 1-C drop in water temperature in the 1980s to the cod collapse, but the scientists note the water has returned to normal or above-normal temperatures.
The Science paper says it is "an open question" whether the ecosystem changes are reversible.
Frank said in an interview the system is far too complex to understand. But he believes the crab, shrimp and small fish are preventing the cod from reproducing successfully. "The little guys have got a lock on the system that makes recovery difficult," he says, explaining that the new dominant species are swallowing the young the cod manage to produce.
The demise of cod stocks is widely seen as an ecological disaster. But Nova Scotian fishers are making more money fishing shrimp and snow crab than they did fishing cod, says Frank.
Ecological disaster boon for fishers: report
Margaret Munro
CanWest News Service
Friday, June 10, 2005
Overfishing has so profoundly altered Canada's East Coast ecosystem it is an open question whether the cod will ever return, says a study on the demise of one of the world's greatest fisheries.
Small fish and bottom-feeders, such as crab and shrimp, have flourished in the cod's absence and appear to have a "lock on the system" that is preventing recovery, says Kenneth Frank, a senior scientist with the federal Fisheries Department. He is the lead author of the report published today in the journal Science.
The study details how the decimation of cod stocks in the 1990s has had a domino effect which radically restructured the marine food web. This is the first time such a "trophic cascade" has been documented in an open-ocean ecosystem.
Cod was for centuries the most abundant predator in the East Coast marine ecosystem and supported a thriving fishery. The stocks, which were still plentiful in the early 1980s, crashed a few years later and a moratorium was placed on cod fishing in 1993.
Fish managers and fishing communities hoped the cod would bounce back if nets were kept out of the water for a few years. But 12 years into the moratorium, the cod show no sign of recovery and key stocks are listed as endangered and threatened.
Frank and his colleagues at the Bedford Institute of Oceanography and Queen's University doubt there will be a recovery any time soon, given the "new fishery regime" which has evolved in the cod's absence. The best hope, says Frank, is to set up a network of marine protected areas to aid recovery.
Frank and his colleagues combed through 40 years worth of data showing changes reverberating across the food web as the cod disappeared from prime fishing grounds on the eastern Scotian Shelf off Nova Scotia. Frank says there is evidence the same kind of domino effect hit the Grand Banks, Gulf of Labrador and Labrador Shelf.
Snow crab, shrimp and small fish, such as herring, capelin and sand lance flourished on the Scotian Shelf in the absence of the predatory cod. The seal population boomed as the animals feasted on the abundant smaller species. Insect-like zooplankton dropped by as much as 45 per cent because the proliferating crab, shrimp and small fish gobble them up. This in turn boosted levels of plankton, which were no longer grazed on as heavily by zooplankton. And the nitrate level in seawater dropped as the flourishing plankton sucked up more of the nutrient.
The scientists say the restructuring likely explains why the cod-fishing moratorium, which has been coupled with improved environmental conditions, has failed to bring back the cod. Some observers had linked a 1-C drop in water temperature in the 1980s to the cod collapse, but the scientists note the water has returned to normal or above-normal temperatures.
The Science paper says it is "an open question" whether the ecosystem changes are reversible.
Frank said in an interview the system is far too complex to understand. But he believes the crab, shrimp and small fish are preventing the cod from reproducing successfully. "The little guys have got a lock on the system that makes recovery difficult," he says, explaining that the new dominant species are swallowing the young the cod manage to produce.
The demise of cod stocks is widely seen as an ecological disaster. But Nova Scotian fishers are making more money fishing shrimp and snow crab than they did fishing cod, says Frank.
I think it's bad news that we've overfished the species to near extinction. (and a yummy species it is) It's not like crabs and shrimp were hard to come by before. With proper ocean and fisheries management, it didn't have to be this way.