Maintaining a healthy population of blue crabs, the Bay's most economically valuable species, means more than just regulating the crab catch. It means maintaining a healthy habitat, too.
That is the message in the Bay Program's new Blue Crab Fishery Management Plan, which stresses for the first time that improving habitat - particularly the amount of grassbeds - is critical to the species.
The goal of fishery management plans is to maintain the stock at levels that optimize harvests while assuring that the overall health of the population, and its ecological role, are maintained.
Historically, that has been done primarily through regulating the catch, and controlling harvest pressure remains an important part of the plan. But it also lays out specific restoration goals for water quality - such as oxygen concentrations - and for grassbeds as a means of protecting the stock.
"This makes it into much more of an ecosystem management plan, rather than just a fish harvest management plan, and I think that is definitely a step in the right direction," said Elizabeth Gillelan, director of the National Oceanic and Atmospheric Administration's Chesapeake Bay Office. "It's a major improvement."
Because the Bay fishery management plans are signed by members of the Chesapeake Executive Council - the governors of Maryland, Virginia and Pennsylvania; the mayor of the District of Columbia; the EPA administrator and the chairman of the Chesapeake Bay Commission - officials say the incorporation of habitat issues gives them added weight.
"This is the first fishery management plan that has integrated specific habitat objectives," said Bill MacDonald, Maryland director of the Chesapeake Bay Commission, which represents the legislatures of the three states and organized a special bi-state panel to help coordinate crab management efforts. "They may be in other Bay Program literature, but they haven't been incorporated into the fishery management plans which tie into the regulatory structure of the jurisdictions."
The plan identifies specific areas where grassbeds are especially important for juvenile crabs, and says those sites should be targeted for restoration and protected from any activity that could degrade their quality.
Grassbeds are the habitat of choice for juvenile crabs, and are found there at densities 30 times greater than in unvegetated areas. Baywide, the plan says it is estimated that five times as many juvenile crabs live in grassbeds as unvegetated areas, although the beds cover only a fraction of the Chesapeake.
Grasses provide refuge where juveniles can hide from a wide array of predators, and studies indicate that crabs in grassbeds grow faster than others.
Beds in the lower Bay are particularly important because they are the first cover available for small crabs as they re-enter the Bay after spending their larval period off the coast. As crabs grow and move up the Bay, they continue to use grassbeds for habitat, as well as salt marshes and the woody debris found in the water adjacent to forested shorelines.
Studies of lobsters in Maine indicate that the availability of habitat for larvae is the most important factor in determining population size for that species, the plan notes.
Though that connection has not been made in the Bay, Rom Lipcius, a researcher at the Virginia Institute of Marine Science who studies crab ecology, said more grassbeds could increase the size of the crab population, especially in years where there are large numbers of juveniles in the population and there is not enough grass cover for all of them. Lipcius noted that crab survival is "substantially higher" for those living in the beds compared with those outside.
"If you enhance habitat, you are providing the optimal conditions for the blue crab," Lipcius said. "So you can't lose, but you may gain. It's almost like an insurance policy. In some years you don't need it, but in other years you do."
The plan is the first update to the Baywide blue crab management strategy since 1989. It cautions that the stock is "fully exploited" at present. And while it calls for no new additional regulations beyond those being implemented by the states to cap fishing pressure, it calls for cautious management to prevent any increase in the fishing mortality rate.
The plan is designed to coordinate fishery management efforts in Maryland, Virginia and the Potomac River, which is managed separately from the two states.
"It's probably the best Bay Program fishery management plan," said Bill Goldsborough, a fisheries scientist with the Chesapeake Bay Foundation. "And yet, having said that, there is still room for improvement."
While outlining plans to control harvest pressure and improve habitat to maintain the stock, Goldsborough said the plan failed to describe in quantitative terms what constitutes a healthy crab population. Such a number, he said, whether based on population estimates or other criteria, could be used by managers to respond to fluctuations in the size of the stock - liberalizing regulations when the stock is large, and strengthening them when numbers decline.
The plan does set a goal for developing targets in the future for "safe management levels."
"I think that's pretty important," Goldsborough said. "You need biologically based triggers for management."
The Bay historically has accounted for more than half of the nation's total blue crab harvest, and its total dollar value is greater than any other fishery in the Chesapeake. The average annual catch is 86 million pounds. Landings hit a low of 53 million pounds in 1992, and a high of 107 million pounds in 1993. Landings were below average in both 1995 (68 million pounds) and 1994 (75 million pounds.)
Nonetheless, a recent scientific assessment of the blue crab stock - the first Baywide assessment ever made - found that the population appeared stable over the past several decades. In fact, it concluded that the population was higher than average during much of the 1980s, and in the last few years had returned to average levels.
According to the stock assessment, about 10 percent of the crab stock has to survive each year to ensure an adequate number of young are produced to sustain the stock. Fishing pressure has been near - but not over - that mark for decades, with no trend on the overall fishing mortality rate, the stock assessment reported.
Because pressure is "very close" to that mark, the management plan says "a conservative approach to blue crab management in Chesapeake Bay is recommended."
The plan cites a number of factors for concern. Though both Maryland and Virginia have moved to limit the number of commercial fishing licenses issued, many commercial fishermen are either not participating in the fishery, or are not using as much equipment as they are allowed. That means fishing pressure could increase without any new licenses being issued, the plan notes.
An even greater concern, may be an improvement in the effectiveness of fishing gear- perhaps through more effective crab pots or baits - which could allow the same number of crabbers to take more crabs. The plan calls on the states to monitor the effectiveness of any new gear that comes into use.
Commercial fishing pressure has increased about five-fold since World War II, though the level of catch has remained about the same, the plan says. As a result, the blue crab fishery is greatly overcapitalized. "In its current state, participants in the fishery are deploying more gear and working harder to catch an equivalent portion of the available stock."
Though increased fishing pressure has not resulted in "recruitment overfishing" - taking so many reproducing crabs from the population that it threatens the stock - the plan cites concerns by some that the Bay may be suffering from "growth overfishing."
Growth overfishing occurs when much of the population is caught close to the minimum size. If crabs were allowed to grow larger before being harvested, the total catch measured by weight - and therefore the total value of the catch - would increase. One recent analysis documented a steady decline in the size of male crabs from 1968 to 1995. Growth overfishing was cited as a probable cause.
Growth overfishing is considered more of an economic issue than one that threatens the health of the stock. The plan says there is "no consensus" among scientists over the implications of growth overfishing, and says the issue "will continue to be revisited" in upcoming years.
"It is something that we definitely need to take a look at," said Carolyn Watson, of the Maryland Department of Natural Resources and the chair of the Bay Program's Living Resources Subcommittee, which oversees fishery management plan development. "Some scientists are seeing evidence that the overall size of the crab is declining over time, yet others don't see the same trend. Are we pulling out crabs as soon as they become legal and therefore, over time, reducing the overall size of the crab in the Bay? I don't know the answer to that, but I think it absolutely needs to be looked at further. It's not something we can turn our backs on."
The plan also says that more work is needed to estimate the size and impact of the recreational crab fishery. "Little is known about the blue crab recreational catch, fishing effort and the economic impact of recreationalcrabbing in Chesapeake Bay," it says. Virginia requires recreational licenses for crabbers, which helps it track recreational activity, and the plan suggestssimilar licenses in Maryland and the Potomac River.