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Shark, Cod, and Other Fish Populations Drop 90 Percent in North Atlantic and Other Areas

February 09, 2005

Predatory fish populations continue to spiral downward, with many dropping 90 percent or more in the past 40 to 50 years, according to a new study in the Philosophical Transactions of the Royal Society's Biological Sciences, published by the United Kingdom's national academy of science.

In a sequel to an earlier highly discussed study showing a significant depletion of predatory fish communities worldwide, originally published in Nature, Ransom Myers and Boris Worm of Dalhousie University in Nova Scotia provide additional population data for sharks, tuna, billfish and the North Atlantic cod which has shown dramatic declines throughout the region.

"Industrial fisheries have changed marine ecosystems in fundamental ways," says Professor Myers. "Current fishing mortalities projected into the future could lead to the extinction of certain sensitive species of sharks and other large predators at the top of the food web."

Sharks are particularly vulnerable to extinction because they grow very slowly, take a long time to mature to their reproductive years, and produce few young. More prolific species such as cod and billfish are vulnerable because, although they produce many eggs, very few survive to reach reproductive maturity. Sharks and billfish frequently are caught as bycatch along with targeted food fish such as swordfish and tuna, which also are depleted in certain areas of the North Atlantic.

Funded by the Pew Institute for Ocean Science and the Census of Marine Life, Myers and Worm's "Extinction, Survival, or Recovery of Large Predatory Fishes" analyzes population data on many species in areas around the world and looks specifically at the many communities of North Atlantic cod, a favorite of commercial fishing operations for decades. Some areas such as the Grand Banks and other areas off of Canada showed a 90 to 99 percent depletion of the cod population.

Closures in some of those areas helped the recovery of haddock and other species, but cod have not bounced back as well. To halt or reverse further declines, the authors suggest several strategies:

  • Reduce fishing mortality enough to avoid extinction of the most sensitive species;
  • Reduce bycatch mortality wherever possible;
  • Use spatial closures to initiate recovery;
  • Establish permanently closed marine ecosystems in key areas, such as spawning grounds and certain hot spots with a diverse population of species.

"There's an important lesson in this paper," says Ellen Pikitch, executive director of the Pew Institute for Ocean Science, which funded the Pew Shark Assessment, and a professor at the University of Miami Rosenstiel School of Marine and Atmospheric Science. "The management actions taken today will determine whether we enjoy biologically diverse and economically profitable fish communities 20 or 50 years from now, or whether we look back on a history of collapse and irreversible extinction."

An expert in fishery management, Professor Pikitch described a new ecosystem-based approach to fishery management in an article published last year in Science. Ecosystem-based fishery management reverses the order of management priorities so that maintaining healthy ecosystems, rather than maximizing catches species by species, is paramount. This approach specifically addresses the impacts of fishing on habitat, non-target species, and ecosystem processes.

"Policymakers need to consider the broader ecosystem in their decision making, to facilitate the recovery of severely depleted fish populations that Professors Myers and Worm have described," says Pikitch. "Collateral impacts of fishing on ocean habitats and biological communities could contribute to the observed failure of fish populations, such as cod, to recover."

Pew Institute for Ocean Science, in partnership with the University of Miami Rosenstiel School of Marine and Atmospheric Science, was founded in 2003 thanks to a multi-year grant from the Pew Charitable Trusts to undertake, sponsor, and promote world-class scientific activity aimed at protecting the world's oceans and the species that inhabit them. The scientific role of the Institute is to increase public understanding of the causes and the consequences of problems affecting the marine environment. The conservation role is to promote solutions to these problems. For more information, visit www.pewoceanscience.org.

Professor Myers holds the Killam Chair of Ocean Studies at Dalhousie University. He received his B.Sc. in Physics from Rice University, and his M.Sc. in Mathematics and Ph.D. in Biology from Dalhousie. Currently researching extinction in the ocean, Professor Myers has published more than 100 refereed scientific publications in diverse fields of aquatic ecology. For more information about the Global Shark Assessment, visit www.globalshark.ca.

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