The Chesapeake's blue crab population is neither over fished nor appears to be undergoing a significant long-term population decline, according to a panel of scientists who undertook an exhaustive review of the stock's health.
While adult blue crab numbers have dropped in recent years, that decline is not dramatic when viewed in the long-term context of the crab population levels, concluded the first-ever "stock assessment" of the Bay's crab population.
Still, the panel cautioned that blue crabs are short lived so managers need to take a "risk averse" -- or conservative -- approach toward management because they would have little time to take protective actions in the event of a sudden, sharp decline.
"This is good news about the status of the stock and reassuring news that there is no evidence of over fishing," said M. Elizabeth Gillelan, director of the National Oceanic and Atmospheric Administration's Chesapeake Bay Office. "But these results shouldn't be interpreted to mean that we can now be complacent about controlling fishing effort. In fact it is critical that we ensure proper controls are in place to prevent over fishing in times of low abundance."
The nine-member group, which was convened by NOAA's Chesapeake Bay Stock Assessment Committee (CBSAC), reviewed a variety of data collected since World War II to assemble a long-term view of the blue crab's health and used computer models to analyze whether fishing pressure was affecting the population.
Their final conclusions were similar to preliminary findings presented last September, but the panel continued to analyze additional data through the fall.
Last December, those results were presented separately to a meeting of Bay region scientists and to CBSAC, which includes federal and state fisheries officials and scientists. A written final report of the panel is expected after an independent peer review in February.
Blue crabs are the Bay's most valuable species, supporting a fishery worth about $187 million a year in the two states.
Concern about the health of the blue crab stock had grown in recent years as fishing pressure increased and several seasons of low catches were reported. A NOAA-funded Baywide winter dredge survey which was begun by the states in the late 1980s to provide better information about the blue crab stock also showed a 34 percent decrease in adult crab abundance between 1990 and 1995.
Those results fueled concerns by some scientists that blue crab catches, which were gradually increasing as other Bay fisheries declined, were taking too many females out of the population before they could reproduce.
But the stock assessment panel found no evidence that current fishing levels on female crabs are threatening the populations reproduction potential. The stock assessment found that "recruitment" -- the number of young crabs -- is now higher than the long-term average. The abundance of young crabs also explains concerns about the decreasing size of crabs -- increased numbers of small, young crabs means the average size of crabs in the population is smaller, not necessarily that there are fewer large crabs.
The stock assessment panel agreed that the adult crab population had declined in recent years, but noted that the decline was measured from a period of unusually high blue crab abundance in during the 1980s.
In analyzing a variety of data from the past several decades, the scientists concluded that the present stock level is actually near its long-term average, and not close to its low, which was reported in 1968.
Blue crabs live throughout the Bay. In the fall and spring, females migrate to the mouth of the Chesapeake where they release their eggs. A single female may contain between 750,000 to 8 million eggs.
The larval crabs live near the surface of coastal waters outside the Bay for several weeks before returning to the Chesapeake. Because of the huge reproductive potential of an individual crab, the stock assessment panel agreed with earlier studies which concluded environmental conditions during the period crab larvae are in coastal waters -- not fishing pressure -- is the primary factor in determining their abundance.
The panel did agree that, like any species, excessive fishing pressure could impact the crab stock, and they identified "threshold" levels of fishing mortality above which the health of the stock would be jeopardized.
When that threshold was compared with three decades of fishing data, the scientists found that fishing pressure had never reached that critical point, though in some years it was approached.
CBSAC suggested a cautious management approach that would cap fishing pressure at or near present levels. Unlike longer-lived finfish, such as striped bass, where managers have several years to respond to stock declines, management actions would need to be taken more quickly for blue crabs, it noted.
L. Eugene Cronin, the former director of the University of Maryland's Chesapeake Biological Laboratory, who conducted numerous crab research projects in the past, said the panel's conclusion that recent changes in crab abundance were not related to over fishing was "within reason."
But, he added, "I don't think we can conclude that and use that as [the only] basis for long-term management. It's another signal."
Cronin said it is not surprising that scientists have reached varying conclusions about the crab stock in the past year because there has been no long-term Baywide monitoring. Instead, scientists are left analyzing crab data that was often collected for other purposes, or which represent only portions of the Bay or its crab population.
"It is an extremely difficult task because we didn't collect the information that they need," said Cronin, who had examined some of the stock assessment panel's conclusions. "I think it's an important study [but] I think we should not jump too fast on this one, as we should not have jumped too fast on some others."
Cronin said the recent concerns over the health of the blue crab stock point to the need for a Baywide monitoring and research program for the species -- something he first advocated in 1947.
"We don't have the quality of information on the stocks for the last 30 years that we should have had," Cronin said. "We knew we needed it, but other things took priority. When things are bad, everyone is willing to promise all sorts of activity. If they recover, as they have so often in the past, they don't do it."
CBSAC hoped to resolve the monitoring problem with its winter dredge survey, though the future of that effort is in doubt because of federal budget cutbacks.
Bill Goldsborough, a fisheries scientist with the Chesapeake Bay Foundation, argued that the results of the stock assessment support "the notion that we have to be conservative in managing the fishery in order to avert a crisis."
Goldsborough said the stock assessment supported the recommendation of the Bay Program's last blue crab management plan -- never fully implemented -- that fishing effort on the crab population should be capped.
In particular, he said, management efforts that limit the number of watermen would help assure each was able to catch enough crabs to make a living -- something that could help stem pressure to over harvest the species. Additional regulations now being considered in Virginia and Maryland "will really take us largely to the point where we can manage effort in the fisheries," he said.
Information from the stock assessment will be used by state fisheries officials to develop blue crab management strategies and in the development of a new Baywide blue crab management plan. Using the stock assessment information, along with socioeconomic information, managers can determine how catch levels should be allocated between the states, between commercial and recreational users, and what types of harvesting techniques should be used.
The Virginia Marine Resources Commission in January was considering a variety of measures to protect blue crabs. Last fall, the Maryland Department of Natural Resources enacted "emergency" regulations that stemmed the female crab harvest by 33 percent. Maryland officials are planning other restrictions to go into effect this spring.
The scientists on the panel came from the Maryland Department of Natural Resources, Virginia Institute of Marine Science, NOAA's National Marine Fisheries Service, the Virginia Marine Resources Commission and the Connecticut Department of Environmental Protection.