Show me the Bait!

The smallest fish in the sea are more than twice as valuable when they’re eaten by bigger fish than when they’re caught by humans, according to a report released Sunday by a scientific task force.

The 120-page analysis by the Lenfest Forage Fish Task Force — a group of 13 scientists specializing in everything from fish ecology to marine mammals and seabirds — underscores the growing concern researchers have about the fate of forage fish, including anchovies, menhaden, herring and sardines that serve as food for bigger fish, sea birds and marine mammals.

Forage fish account for 37 percent of the world’s commercial fish catch, with an annual value of $5.6 billion. (Only 10 percent of forage fish caught are eaten by humans; the remaining 90 percent are processed into fish meal and fish oil, which feed livestock and farmed fish.)

But the team of scientists, who worked for three years on their analysis, concluded that forage fish support $11.3 billion worth of commercial fish by serving as their prey. In the North Sea, for example, sand eels help sustain cod, and tuna in the eastern tropical Pacific Ocean feed on sardines.

The group’s economic analysis did not include the value forage fish provide to sea birds and marine mammals, many of which are highly dependent on them. University of Washington conservation biologist Dee Boersma, one of the task force’s members, has conducted studies showing that the breeding success of Magellanic penguins is directly related to how far they had to forage for food. If they could find fish between 30 and 50 miles of their colony they produced two chicks; if they had to travel more than 90 miles away, they had one; and if they had to go 125 miles, they had none.

In an interview, Boersma said that with fewer forage fish, seabirds were having to travel farther for less food. “Suddenly, instead of 90 percent, you’re settling for 10 percent. That’s what’s happening to seabirds. When fish is not there, they don’t do as well.”

Ellen Pikitch, chairman of the task force and executive director of Stony Brook University’s Institute for Ocean Conservation Science, said society may need to reassess its reliance on small marine species to sustain the growing aquaculture trade. Farmed fish accounts for roughly half of the world’s commercially sold fish.

“People don’t understand how massive this fishery is,” Pikitch said, referring to how many forage fish are processed. “It seems we may be on a collision course at some point, where increased demand is going to pull the rug out from under the ocean ecosystem.”

The issue has become increasingly important for fishery managers in the mid-Atlantic, who voted in November to cut the amount of menhaden that can be harvested annually from 183,000 metric tons to 174,000, out of concern that the fish have been depleted.

One company, Omega Protein, took 160,000 metric tons of menhaden — 80 percent of about 450 million fish harvested in 2010 — off the coast of Virginia, which is the only state that allows industrial fishing of menhaden.

Edward D. Houde, a task force member and a professor at the University of Maryland’s Center for Environmental Science at the Chesapeake Biological Laboratory, said the task force concluded that fishery managers should leave at least 40 percent of adult forage fish in the sea. Menhaden support a range of species in the Chesapeake Bay and Atlantic Ocean, including striped bass, osprey, bald eagles and brown pelicans.

Traditionally, fishery managers aim to leave 20 percent of adult fish unexploited. The Atlantic States Marine Fisheries Commission will finalize its menhaden rule next year, and is crafting limits that would ensure at least 15 percent of adult menhaden, and perhaps as much as 30 percent, are left to spawn in the ocean and its tributaries after the yearly harvest. Current limits are to leave at least 8 percent.

“That would not be as precautionary as we’re recommending in the task force,” Houde said, though he said it was a step in the right direction. “It’s still very hard for them to reduce fishing, which means reducing catches and reducing profits. It’s not easy for them to take these precautionary steps that are important for the environment.”

An international group of marine scientists is calling for cuts in commercial fishing for sardines, herring and other so-called forage fish whose use as food for fish farms is soaring. The catch should be cut in half for some fisheries, the scientists say, to protect populations of both the fish and the natural predators that depend on them.

“The message is, if you cut back on harvesting of forage fish, there will be benefits,” said Ellen K. Pikitch, director of the Institute for Ocean Conservation Science at Stony Brook University and chairwoman of the task force that produced a report on the issue that was released Sunday.

The report, “Little Fish, Big Impact,” financed by the Lenfest Foundation through the Pew Charitable Trusts, details how fishing has increased for these fish, which now account for 37 percent, by weight, of all fish harvested worldwide, up from about 8 percent half a century ago. The consumer market for forage fish is relatively small; most of the fish are ground and processed for use as animal feed and nutritional supplements and, increasingly, as feed for the aquaculture industry, which now produces about half of all the fish and shellfish that people eat.

Forage fish are an important link in the food chain, eating plankton and being consumed, in turn, by large fish like tuna and cod, as well as by seabirds and dolphins and other marine mammals. The task force estimated that as a source of food in the wild for larger commercially valuable fish, forage fish were worth more than $11 billion, or twice as much as their worth when processed for aquaculture and other uses.

“Sometimes the value of leaving fish in the water can be greater than taking it out,” Ms. Pikitch said.

The report cites several cases in which overfishing of forage fish has led to the collapse of populations of larger fish or other predators, and suggests that such cases could increase unless catches are reduced.

On the East Coast, the fishery for menhaden, a forage fish, is the largest in the region, and about 80 percent of the catch is processed into meal and other products. The abundance of menhaden has declined over the last quarter-century, said Edward D. Houde, a professor at the University of Maryland Center for Environmental Science and a member of the task force, as the fish’s reproductive rate has fallen. Yet fishing has continued at a high rate.

Bob Beal, an official with the Atlantic States Marine Fisheries Commission, a regional group that coordinates management plans for the menhaden and other fisheries, said that in 2010, the menhaden population was estimated to have been reduced to 8 percent of its maximum potential. As a result, Mr. Beal said, the commission has recommended reducing the allowable catch so that the population roughly doubles, to a threshold of 15 percent of the maximum level, with an eventual target of 30 percent. The reductions would take place next spring, after a period to allow for public comments on the proposal.

But Mr. Houde said that in the case of menhaden, the task force would recommend a threshold of 30 percent and a target of perhaps 40 percent, which would mean even greater catch reductions. “Our recommendation is to be very precautionary,” he said, “mostly to protect other things in the ecosystem, but also to protect the fish itself.”

Mr. Beal said while the commission’s new plan for the menhaden fishery is not as conservative as some scientists have sought, “it’s a pretty big departure from where it’s been managed.” He said that the commission had to weigh the needs of the fishing industry as well.

“Ultimately, the hope of the managers is to rebuild the stock,” he said, “so the industry can get what they want out of it, and prey animals can get what they want out of it, too.”