|
Monday, June 27, 2005
Decline in codfish stocks may not be reversible
Copyright © 2005 Blethen Maine Newspapers Inc. | ||
 |
||
The collapse of cod stocks off the coast of Nova Scotia more than a decade ago has so altered the marine ecosystem that cod's recovery may be impossible, according to a new study by a group of Canadian scientists. "It was always thought that the effects of overfishing were reversible," said Ken Frank, who co-authored the report published recently in Science magazine. "It's pretty shocking when you stop fishing, the fish don't return." The research of Frank, Brian Petrie, Jae Choi and William Leggett could have ramifications for Georges Bank cod, which also has been decimated by overfishing. Their findings, based on 40 years of data, echo what many other scientists have found - that the ocean's animals and plants relate to each other in a complex web that humans have only begun to understand. Once the top predator, cod is now a bit player. Its population on the Scotian Shelf has plunged 96 percent since the 1850s, according to archaeological evidence and old fishing records. In its absence, the entire marine ecosystem has been transformed, Frank argues. Frank, who works for Canada's Department of Fisheries and Oceans at the Bedford Institute of Oceanography, says the virtual disappearance of cod - and other large species such as haddock, flounder and hake - led to what scientists call a "cascade effect." That is, as the population of large predators declines, the fish they prey on - herring, shrimp, crab and lobster - undergo a population explosion. Cod, which used to sit on the top of the food chain, has now been replaced by smaller fish that are dominating the marine world. Cod's departure is felt at the very bottom of the food chain, Frank says. Zooplankton and algae are now being depleted at a faster rate because more and more fish are feeding on them, he says. Eventually, the lack of food could bring about a crash in the numbers of fish, he says. Frank says it's unclear whether cod can make a recovery in this new environment. A big obstacle, he says, is that cod spend the early parts of their lives at the bottom of the food chain. Cod eggs, larvae and juvenile cod are food for other fish. Because there are fewer adult cod, there are now a larger population of fish to eat the young cod. "The king of the jungle are typically large as adults and are safe," said Robert Steneck, a University of Maine scientist who has studied the cascading effect in the Gulf of Maine. "With overfishing, we are left with babies, and they are not safe." Even under optimal conditions, of the several million eggs each female cod spawns, only about one egg of each million succeeds in completing the cycle to become a mature cod. On the Scotia Shelf, cod have an even worse chance of surviving to adulthood. With the departure of the top predator, the populations of its former prey are now expanding to record levels. In Newfoundland waters, the snow crab is thriving and Newfoundland fishermen are making more money fishing for snow crab than they ever did fishing for cod. The same thing is happening in the Gulf of Maine with lobster, a favorite prey of cod. Because of cod's decline, lobster populations have exploded to record levels, despite increasing fishing pressure, Steneck says. And lobsters today account for more than 70 percent of the total value of Maine's marine resources. While that may seem like great news, Steneck says, fishing communities have become dangerously dependent on lobsters. "If anything happens to this one species, we have a disaster on our coast," he said. Frank says the story of cod on the Scotian Shelf shows that mistakes in fisheries management can cause irreversible changes in the ecosystem. "When groundfish stocks collapsed, we stopped fishing," he said. "We thought that by removing man from the system, it would allow cod to return. It hasn't happened." Staff Writer Tom Bell can be contacted at 791-6369 or at:
|
||