The Bay blue crabs population has been relatively stable for decades while the juvenile population has been increasing in recent years, despite a dramatic increase in commercial fishing effort.
Those are some of the findings of the first comprehensive Baywide blue crab stock assessment, completed for the Chesapeake Bay Stock Assessment Committee (CBSAC), a state-federal group coordinated and funded by the National Oceanic and Atmospheric Administration's Chesapeake Bay Office.
The assessment's overall conclusions, which drew on a variety of research, monitoring and computer modeling data, include:
- The Baywide crab population is demonstrating long-term dynamic equilibrium. Current stock abundance is at the long-term average measured since mid-1950s. No conspicuous declining trend in abundance is demonstrated; nor are demonstrable sex-specific differences in these trends observed.
- The blue crab juvenile population has been increasing the last decade and currently is above the long-term average measured during the past four decades. The stock is providing near maximum sustainable yield to the Baywide commercial fisheries.
- The Baywide blue crab stock is considered to be moderately to fully exploited. Current fishing mortality rates are less than threshold values deemed appropriate for this stock. No evidence of overexploitation or of significant differences in fishing mortality between male and female blue crabs were observed.
- Since 1945, a five-fold increase in fishing effort has occurred in the combined commercial fisheries of the Bay. Despite this dramatic rise in effort, fishing mortality has remained relatively constant over the long term as a result of gear saturation and/or gear competition.
- The Chesapeake Bay blue crab fishery is severely overcapitalized in terms of the quantity of gear applied to the harvest. The combined fisheries are operating at extremely low levels of economic efficiency, with a relatively constant harvest divided into increasing numbers of gear units.
The blue crab stock assessment began in July 1995, in part out of concerns raised about the status of the blue crab population in the Bay. The assessment report was written by nine state and federal fishery scientists serving on CBSAC's Technical Subcommittee, chaired by Dr. Louis Rugolo, Maryland Department of Natural Resources.
"With new interest in coordinated multistate management of blue crabs, this Baywide assessment will be an important scientific foundation for future blue crab policies," said Elizabeth Gillelan, director of the NOAA Chesapeake Bay Office and chair of CBSAC.
Not all scientists agree with the finding that stock levels have remained steady for decades. Annual surveys conducted by the Virginia Institute of Marine Science indicate that crab abundance in the Bay declined after Tropical Storm Agnes in 1972, and has not returned to its previous level.
"Regardless of the status of the stock, we both agree that the spawning stock is a very productive stock," said Rom Lipcius, a leading crab researcher at VIMS. "Our primary concern is that the spawning stock may not be as well off as suggested by the stock assessment. But if we cap effort, we feel fairly comfortable that it can persist over the long term, though we would like to have a bit more research directed at it."
The new Chesapeake Bay Blue Crab Fishery Management Plan calls for the stock assessment to be updated in two years, and then every five years after that.
The stock assessment identified specific areas of research to be pursued and information to be gathered to refine key components of subsequent assessments. These include methods to determine the age of a blue crab, tagging studies to improve estimates of natural mortality, and improved recreational and commercial fishery data. The next assessment will further examine growth overfishing, blue crab growth and longevity, and strategies to maximize the yield from this valuable fishery resource.