One of the Bay's most important fish species may be in the midst of a coastwide decline that some worry could have ripple effects for other species, such as striped bass.
The concern is over the Atlantic menhaden, historically one of the most abundant species in the Chesapeake and along the coast. But the number of young menhaden has declined for several years, and the adult population has started to fall as well.
"I've been picking Atlantic menhaden out of gill nets for 40 years, ever since I was a kid," said Jim Price, a retired charter boat captain and president of the Chesapeake Bay Acid Rain Foundation. "I know when they're abundant. I know when they're not abundant. And in the past six or eight years, they've steadily declined in the Maryland portion of the Bay."
"The stock is collapsing right now," Price said. He cited figures showing that Virginia pound net menhaden landings fell 74 percent from 1981 to 1996, while menhaden in the the Maryland young-of-year survey showed a 90 percent drop over the same period.
Others are not so blunt in their assessment, but there is a growing concern over the health of the stock.
Attention has focused on menhaden in large part out of concern over striped bass. Last fall, surveys found surprisingly high numbers of adult striped bass - nearly 12 percent in Maryland Department of Natural Resources surveys - disfigured with deep, ugly lesions.
Some have hypothesized that the fish became infected because they were under stress in the Bay, possibly because there was not enough food.Lately, the dropping menhaden stock has been suggested as a potential explanation. "It's the striped bass sores that triggered it, but that's not really the story anymore," said Jim Uphoff, a DNR biologist who has studied striped bass for years.
Menhaden typically are the largest source of food for striped bass. But a number of striped bass examined by Price last fall, and turned over to the DNR, had little body fat and little or no food in their stomachs - and almost no sign of menhaden.
The issue of what triggered the striped bass sores - and drop in menhaden - has been the subject of presentations at several recent Bay Program meetings.
But fisheries managers say the menhaden picture is not clear-cut. Menhaden reproduction has declined sharply for several years in a row, last year dropping below a management "trigger" set by the Atlantic States Marine Fisheries Commission, a compact of East Coast states that manages migratory species. Hitting the trigger sparked concern about the stock's health, but last year the ASMFC panel overseeing menhaden concluded no action was warranted.
The reason was that while reproduction was poor, the "spawning stock" - an estimate of the population's reproductive potential - has been been considered to be in good condition. In 1996, though, the spawning stock began to fall. Data for 1997 is now being reviewed.
"If that shows a continued decline, ASMFC's Atlantic Menhaden Management Board may have to take some action," said Joe Desfosse, ASMFC fishery management plan coordinator.
Doug Vaughan, a biologist with the National Marine Fisheries Service who monitors the menhaden stock, agreed. "With spawning stock being high, we can't say the stock is in trouble," he said. "But we're certainly very concerned because if we don't get some good recruitment [reproduction], then it will be in trouble in a few years. If the spawning stock eroded to lower levels, I think it would be felt something needs to be done."
That could mean curtailing the commercial menhaden fishery. If enough young fish are not coming into the population to maintain the stock, the commercial catch could end up taking too many potential adult spawners out of the population.Price contends the commercial menhaden fishery is already taking too many older fish. Menhaden can live to be about 8 years old, but few found in the population today are older than 6. In the 1950s, when data suggest the menhaden stock was much higher than in recent decades, 8-year-old fish were common.
In terms of quantity, menhaden are one of the most important fisheries in the Bay. The processed fish are used as fish oils and meal for livestock feed.
To some degree, Vaughan and Desfosse noted that fishing pressure is sure to decline somewhat this year because seven menhaden boats - a third of those on the East Coast - are being transferred to the Gulf of Mexico by their owners.
But commercial fishing may not be the only pressure facing menhaden.
Striped bass populations in the Bay, bolstered by several record spawns, are higher than at any point in decades. That raises the question: Are there so many striped bass that they are putting too much pressure on menhaden? Or is the lack of menhaden creating a food shortage for striped bass?
"It's sort of a chicken and egg argument," Vaughan said. "I think it would be just as valid to make an argument that the return to better conditionsof some of the predatory fish is as likely to be causing the problem in the menhaden as vice versa. Right now, I couldn't tell you which is which, and it gets very hard to try to separate it out."
Yet another possibility is that the things larval menhaden like to eat are in decline. Claire Buchanan, an aquatic ecologist with the Interstate Commission on the Potomac River Basin, has observed what she calls a "disturbing trend" toward fewer zooplankton in the middle and lower parts of the Bay in recent years.
Large zooplankton, or "mesozooplankton," which are the main food for larval menhaden, have declined by as much as 75 percent in some areas, Buchanan said. Declines appear to have been going on even longer in the Middle Bay, she said.
"It's an interesting parallel," she said. "At this point, it's just a suggestive cause-and-effect relationship. It needs some more looking into. There's a lot more going on than a simple menhaden crash, and that to me is the worrisome angle of it."
Larval life stages of almost all finfish in the Bay require zooplankton for feeding after they hatch from eggs. Juvenile and adult life stages of other important forage fish - including bay anchovy and Atlantic silverside -continue to feed exclusively on zooplankton throughout their lives. Anchovy and silverside numbers are also declining, Buchanan said.
Some believe the importance of those fish as "forage" for larger predators has grown in recent decades because of sharp declines in the numbers of other forage species, such as blueback herring, shad and alewives. That has made predators even more dependent on the forage species that remain.
Besides being a major food source for predators - from bluefish and weakfish to herons and osprey - menhaden also play other important roles in the Bay. Juveniles and adults form huge schools that swim through the water grazing on algae, removing huge amounts of it from the water. An average adult fish can filter nearly 4 gallons of water a minute as it feeds, which means it would filter plankton from more than a million gallons of water in 180 days. Because of that, they probably play an important role incontrolling algae growth in the Bay.
With the growing numbers of predators - as well as recognition of the menhaden's ecological role - some say more attention needs to be paid to relationships between species when managing menhaden.
"This is probably the dawn of multispecies management," Uphoff said.
But balancing the needs of growing number of predators and the fishing industry could be a tough job because there are so many variables involved, Vaughan said. "It's not an easy issue. And yet I think we're all aware that you can't always handle all these problems on a species-by-species basis."