Declining ocean biodiversity could lead to the collapse of all commercial seafood stocks in the wild by midcentury, said a new international study that involves San Diego scientists.
JOHN GIBBINS / Union-Tribune
Enrique Meza unloaded opah, a type of sunfish, near the Chesapeake Fish Co. at Seaport Village on Wednesday.
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The finding came from a comprehensive examination of how a global fall in marine biodiversity threatens to unravel the oceans' ability to provide food, fight disease outbreaks, cleanse itself and weather environmental events. It paid particular attention to coastal areas, where most fishing is conducted and pollution is at its worst.
The four-year study includes contributions from researchers at the Scripps Institution of Oceanography at the University of California San Diego. It appears today in the journal Science.
Seafood industry representatives said the biologists are too pessimistic in their predictions of widespread losses for marine stocks.
“All this biodiversity stuff isn't a bunch of tree hugging,” replied Scripps Institution professor Jeremy Jackson, a co-author of the study. “It's real and (the oceans') resilience is fundamentally tied to the biodiversity of the ecosystem.”
Despite the trends highlighted in the report, the oceans have shown a remarkable ability to recover when seafood harvesting is limited, marine habitats are restored and pollution is reduced, the scientists said.
“It's not too late to turn this around,” said Boris Worm, lead author of the paper and a researcher at Dalhousie University in Halifax, Canada.
Worm called for more effective approaches to protecting marine species, including setting aside ocean areas akin to national and state parks.
Also needed, and much more difficult to achieve, is a drastic cut in the amount of pesticides, fertilizers and other toxic chemicals that run from land to the sea, the biologists said.
At the mouth of the Mississippi River, for example, the flow of fertilizers from U.S. farms creates a massive dead zone in the Gulf of Mexico. It starves the water of oxygen and stifles shrimp, fish and other sea life.
Worldwide, urban centers are huge sources of pollutants that eventually stream into the oceans. Closer to home, San Diego faces state fines for failing to adequately reduce storm-drain runoff.
Meanwhile, air pollution from the burning of fossil fuels will be even harder to cut. It contributes to global warming and rains toxins into the seas.
“We're down the line quite a bit,” Worm said. “It looks grim.”
On the other hand, Worm cited actions that are helping to revive marine biodiversity. They include efforts along the Baltic Sea in Europe, where wetlands have been restored and pollution reduced, and the Georges Bank off New England, where the U.S. government has limited fishing.
Some critics of the study said Worm and his colleagues are ignoring the successes of current fisheries management in the United States.
“We disagree substantially with (its) findings ... and others like it suggesting that the ocean is doomed,” said Diane Pleschner-Steele, executive director of the California Wetfish Producers Association.
“A case in point in our favor is the fully recovered and robust status of our Pacific sardine stock,” she said.
The new report is the latest in a string that documents how declining biodiversity is degrading oceans.
“I think this paper is a very important bridge between the doom and gloom of how bad we've made things, and . . . an understanding of how to try fix the problem,” Jackson said.
For their study, the scientists looked at four sets of data gathered from around the world.
JOHN GIBBINS / Union-Tribune
Enrique Meza (left) and Carlos Acuņa brought in locally caught swordfish near Seaport Village on Wednesday.
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First, they examined 32 marine experiments that manipulated the diversity of species on a small scale.
Second, they tracked the 1,000-year history of change in the diversity of ocean species and how this diversity benefits humans – such as providing food and promoting water clarity – in 12 coastal areas in the United States, Canada and Australia. The scientists did so by mining archives, fishery records, sediment cores and archaeological information.
In this second analysis, the biologists found that a biodiversity decline of 50 percent or more reduced the number of viable seafood stocks by 33 percent; degraded nursery habitats such as oyster reefs, seagrass beds and wetlands by 69 percent; and caused a 63 percent drop in the ability of coastal areas to naturally filter and detoxify sea water.
Third, the researchers studied commercial fishing data between 1950 and 2003 for 64 large marine ecosystems worldwide. They found that 29 percent of all marine species commercially harvested in 2003 – the latest year for which statistics were available – had collapsed.
The study's authors regard a fishery as collapsed when its total catch in a given year falls below 10 percent of its recorded maximum yield.
The amount of seafood caught in the 64 ecosystems peaked in 1994 at about 84.7 million metric tons. Despite the growth of fishing fleets and the use of improved technology, total catches in these areas fell 13 percent between 1994 and 2003, the scientists said.
In the last part of their study, the researchers investigated environmental changes in 48 areas where fishing was restricted or banned.
All four analyses pointed in the same direction: the more biodiversity, the healthier the oceans.
“The loss of species is not only harming ecosystems, it's harming our own well-being, our food supply,” Worm said. “The loss of biodiversity erodes the species we can use to our benefit, and it erodes the ability of the system to self-repair and recover on its own.”
While acknowledging that pollution and other environmental pressures are harming seafood stocks, some researchers dispute the role of commercial fishing in this decline.
Commercial fisheries in the wild are managed much better than they were 20 years ago, and to suggest that most of them could crash by midcentury is “just plain silly,” said Ray Hilborn, a professor of aquatic and fishery sciences at the University of Washington in Seattle.
There are many examples of successful fisheries management in the United States, Australia, New Zealand and Iceland, Hilborn said. He recognized that some regions, including those off Asia and Africa, are in trouble because of overfishing.
John Ogden, director of the Florida Institute of Oceanography, said biologists have struggled for years to express how important biodiversity is for the health of the environment – on land and in the seas.
The new study is compelling partly because it brings together evidence from a variety of places to make a comprehensive case for that idea.
“We're cutting our throats in the long run,” Ogden said of doing nothing to protect ocean biodiversity and maintain the health of fish and other seafood. “Why would we want to do that?”
Bruce Lieberman: (619) 293-2836; bruce.lieberman@uniontrib.com
