Scientists say that unless fishing pressure is further reduced on blue crabs, the Chesapeake’s most valuable remaining commercial fishery, the stock could risk a population crash from which it could take years to recover.

The consensus in new round of surveys recently reviewed by a panel of scientists was almost unanimous in indicating that the number of crabs of all ages is decreasing, that mortality caused by fishing is increasing, that the size of crabs is decreasing, and the the population’s spawning stock — those able to reproduce — is below the long-term average.

On top of that, a new analysis completed by scientists from the University of Maryland’s Chesapeake Biological Laboratory shows that fishing pressure on the crabs has exceeded “sustainable” levels for the last five years.

“It is certainly a warning sign that we need to pay attention to,” said Tom Miller, a CBL scientist who did the study along with colleague Ed Houde. “In the long-term, if we are right, the population cannot sustain, that rate of exploitation.”

That’s more cautious than a finding by the Chesapeake Bay Stock Assessment Committee earlier this year, which concluded that the blue crab stock was “fully exploited.” Still, the stock assessment committee’s finding reflected a worsening situation from two years ago when it concluded that crabs in the Bay were not fully exploited.

The key reason for the difference between the stock assessment and Miller and Houde’s analysis dates to 1981. That year, Maryland figures show a huge increase in blue crab landings, a figure that has stayed high until recent years.

According to the stock assessment’s interpretation, the 1980s were a period of high abundance for crabs, and recent declines in landings reflect a return to more typical abundances.

But in their analysis, Miller and Houde contend that Maryland’s change to a more accurate reporting system for landings in 1981 was the primary reason for the increase in reported catches and not just a change in underlying abundance.

Virginia landings showed no surge in 1981, Miller and Houde note, and while some surveys show occasional “spikes” during the 1980s, none indicate a sustained higher abundance of crabs during the decade.

When viewed in that light, Miller and Houde’s analysis shows that declines in recent years are not a return to normal abundances, but a drop below historic levels.

Rom Lipcius, a crab researcher at the Virginia Institute of Marine Science, has — like Miller and Houde — maintained that an accurate picture of the blue crab stock requires an adjustment in Maryland figures since 1981. His estimates have similar conclusions to those of Miller and Houde.

“We actually took a slightly more conservative approach, but they all show the same thing — that the ’80s was not the heyday for blue crabs,” Lipcius said. “In fact the ’60s were the heyday of the fishery in terms of landings.”

“Right now,” he said, “what we’re saying to managers is that we’ve shifted from being concerned to being deeply concerned.”

New concerns about the crab led the Bi-State Blue Crab Advisory Committee — which includes fishery managers from Virginia and Maryland, watermen, industry representatives and others to meet in September, a month earlier than planned. But committee members indicated no changes in management were imminent.

The meeting was called after the Maryland catch dropped sharply in both July and August. Its July landings of 4.6 million pounds were 52 percent below the average July catch of 8.8 million pounds.

But the Potomac River Fishery Commission reported that while July landings were below average, they were not dramatically so. In Virginia, final figures are not available, but officials expected July landings to be below average, but not significantly.

Many committee members indicated they wanted better information before recommending management changes. “Just because we see a drop in the July harvest, we don’t want to go out and cry Chicken Little,” said Bill Pruitt, chairman of the Virginia Marine Resources Commission.

Virginia and Maryland have gone through two rounds of restrictions, imposed in 1994 and 1996, in response to previous declines. The regulations limit the number of watermen who can fish for crabs, restrict the numbers of pots and shorten the crab season. Some managers said Miller and Houde’s analysis did not fully take into account the effectiveness of those regulations.

“To say the management measures have not worked when they have not fully had time to take effect is not correct,” Pruitt said. He cautioned that Miller and Houde’s analysis had not yet been peer-reviewed by other scientists.

Jeff Crockett, a waterman who is on the committee, called Miller’s analysis “unfair” because it made an adjustment for the 1981 reporting change, but not others that have been made over the years.

Crockett argued that the increases after 1981 may have been real — and not just reflect a change in reporting methods — because that was a time when diseases began hammering oyster populations and more watermen turned to crabbing to make a living.

Miller acknowledged that other methods than the one he employed could be used to adjust the 1981 figures than the one he used, but stressed that some adjustment was required. “The original stock assessment, which made no adjustment, was in error,” he said.

Others said increased populations of predators, such as croakers and striped bass, were taking a toll on blue crabs. “The fish, I feel, have eaten up the crabs,” said James Russell, a waterman who sits on the committee.

Scientists who serve on the technical workgroup advising the blue crab committee expressed doubt that fish were taking a major toll on blue crabs. Even if they were, the scientists said, there was little that could be done about it except to reduce fishing pressure on blue crabs and accelerate efforts to plant underwater grass beds, which offer small crabs protection from predators.

Complicating the issue for decision makers and scientists is that managing blue crabs is filled with uncertainties. No one, for example, has yet developed a way to accurately determine a crab’s age, making it difficult for scientists and managers to accurately estimate natural mortality rates in the Bay. Also, no one knows how many crabs are caught by recreational fishermen, or how much that varies from year to year, adding even more uncertainty to population estimates.

Robert Bachman, director of the resource management office of the Maryland Department of Natural Resources’ Fisheries Service, said more restrictions may be needed, but that would not happen until there is a stronger consensus about the depth of the problem. “We first have to demonstrate, conclusively with some good hard numbers, that indeed we are fishing beyond the maximum sustainable yield,” said Bachman, a member of the blue crab committee.

Bachman said the crab population in the Bay still has enough spawning potential that would make any imminent collapse of the population unlikely. “There is reason for concern, but not alarm,” he said.

Miller agreed that his analysis “does give us some time” to take action.

But the analysis warned that the consequences of failing to prevent a population collapse would be dire. In that case, the analysis indicated the exploitation rate on crabs would have to be reduced by at least half, and that recovery could take anywhere from seven to 10 years.

“There is an onus on scientists providing advice to give the most conservative advice they can,” Miller said. “The risk of being overly aggressive in your management is too high.”

Blue Crab Consensus

The panel of scientists that advises the Bi-State Blue Crab Advisory Committee reviewed the most recent surveys at its Sept.3 meeting. They developed the following statements of consensus:

  • Overall abundance for all age groups of blue crabs is down.
  • Fishing mortality is increasing.
  • Fishing effort is at nearrecord levels.
  • Spawning stock biomass (an estimate of the total population’s reproductive potential) is below the long-term average.
  • The average size of crabs is decreasing. The workgroup suspects that once crabs molt to more than 5 inches (the minimum legal size for hard crabs), most are harvested and do not have a chance to grow more than 6 inches.
  • Fishery-independent surveys (those not based on commercial landings) show a decreasing percentage of legal size crabs.
  • The reproductive potential of crabs may be compromised because of the smaller males and lack of mature females.
  • Fishery-independent surveys are important and the long-term data obtained from each is essential in assisting management.
  • Funding for blue crab management, especially the fishery-independent surveys, is a high priority and needs to be maintained and expanded.