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Little Fish Need a Break
2 April 2012 5:49 pm
Fish near the base of the food web need more protection, because these species are an important source of food for seabirds and other predators and are prone to collapse, according to a blue-ribbon panel of scientists. The team has developed specific recommendations that fisheries managers and policymakers can use to set catch levels—some 50% lower—that would not threaten the ecosystem.
The panel says its recommendations could actually boost revenue, because predatory fish like tuna are worth more than the forage fish they eat. "It's a good study by some great people," says fisheries biologist Steven Murawski of the University of South Florida, St. Petersburg, who was not involved. "What they've said needs to be taken seriously." But implementing the suggestions may not be easy.
Forage fish are small species, such as herring and sardines, that eat mostly plankton. They are preyed on by larger fish, seabirds, and other predators. The majority of the 31 million metric tons of forage fish caught—representing 37% of all wild fish captured—are turned into fish oil supplements and feed for aquaculture, poultry, and livestock. But forage fish populations are strongly influenced by ocean conditions and prone to boom and bust cycles. Exacerbating that problem was the steady rise in the total harvest throughout the 20th century. Some forage fish populations, such as sardines off the Pacific coast of the United States, collapsed from overfishing and only very slowly recovered.
The new report, on which 13 eminent scientists spent almost 3 years, was sponsored by the Pew Charitable Trust's Lenfest Ocean Program. Led by Ellen Pikitch of Stony Brook University in New York, the panel reviewed the scientific literature and analyzed computer models of food webs in 72 marine ecosystems around the world. They found that many predators depend heavily on forage fish; three-quarters of the ecosystems they studied had one or more predators for which forage fish made up at least half their diet.
The team used additional models to figure out how much fishing impacts forage stocks and the predators that depend on them. They found that, under the conventional management target called maximum sustainable yield, forage fisheries have a 42% chance of collapsing. If fishing rates are cut in half, the likelihood of collapse falls to 6%. Lessening fishing pressure will also speed their recovery if their populations crash from natural causes. "They have a much better chance of rebounding if you don't hit them when they're down," Pikitch says. Predator populations also benefit from reduced fishing; under conventional management of forage fisheries, predator populations are likely to decline on average 28% over 50 years, compared to an 11% drop if fishing rates are halved. These findings generally match other model results published last year.
The team wanted to come up with recommendations that would provide at least 95% certainty that forage fishing would not put predators at risk of extinction. Using established criteria from the International Union for Conservation of Nature, they calculated the type of fishing management that would be most safe. The best strategy is to gradually tighten fishing limits as the size of the population shrinks. There should also be a hard stop: At no point should fishing remove more than 60% of the population that would be there if no fishing took place. (This is the unfished biomass, defined as the long-term average without fishing.) This strategy has the highest chance of preventing seabird populations, which are the most vulnerable type of predators, from declining badly enough to put them at risk of extinction. In December, one member of the panel published a paper that coined the slogan, "Leave one-third for the birds."
The team also recommends that managers take a precautionary approach to setting targets for population size, arguing that only 20% of unfinished biomass should be removed when data on population dynamics and predators are lacking. That figure rises to 70% for the best-understood fisheries. For the majority of fisheries that fall in between, the amount of fish caught should not exceed 40%, which is half the percentage typically allowed under current standards. This overall approach is incorporated in guidance from the U.S. National Oceanic and Atmospheric Administration, but not necessarily in less well-managed fisheries.
Fishing less could actually have an economic payoff, the team found. The logic is simple: Forage fish are worth more when left in the ocean, because the predatory fish that eat them can be sold for more money. Based on the computer models of 72 ecosystems, the researchers found that the global value of forage fish caught is $5.6 billion a year, while those in the ocean contribute twice that amount to other fisheries. "It will get people to think about fish differently," Pikitch says. "They have an important value in the ecosystem, and that value can translate into big dollars."
Further analysis could result in bigger value, Pikitch adds, if researchers account for benefits to recreational fisheries and ecotourism activities such as whale watching. Ray Hilborn of the University of Washington, Seattle, who wasn't involved, calls the finding "an important result" but suspects that the economic impact of restricting forage fishing will vary depending on the details of the fisheries.
The advice to cut fishing is "reasonable and most likely a very prudent course of action," says Les Kaufmam, an ecologist at Boston University and Conservation International, but it won't be easy to convince some fishing communities. "I expect a lot of pushback on this one because people will perceive their local situations as different." The economic tradeoffs may also vary by locale: Reducing the catch of herring might hurt that segment of the fishing fleet while boosting the bottom line of those who catch salmon.