With the opening of the 2008 blue crab fishing season in the Chesapeake Bay, fisheries managers, watermen, scientists and other interested parties in Maryland and Virginia have been engaged in a debate over new proposals for blue crab fishing regulations. To help inform these discussions, SERC researchers who have spent more than 20 years studying blue crab ecology have issued a white paper on their work on female migration patterns.
For the full paper in pdf, click here >>
Female Blue Crab Migration in Chesapeake Bay
20 May 2008
Anson H. Hines, Robert Aguilar, and Eric G. Johnson
Spatial and temporal patterns of migration by mature female blue crabs in Chesapeake Bay were determined over a 9-year period (1999-2007) with a fishery-dependent tag-recapture program that paid rewards to individual fishers for providing recapture data. The study tagged 8,400 mature female blue crabs and released them in representative subestuaries along the Maryland and Virginia portions of the Bay. Recapture data for 1,526 crabs (18.2 percent average recovery rate) provided clear information about the timing, routes and depths of female migration to lower Bay spawning grounds. Most tagged crabs (947 females or 62.1 percent) were caught before they began to migrate, indicating that the impact of the fishery is greatest prior to female migration. Crabs moving more than 4.2 miles (7 km) from release sites comprised 37.9 percent of the recaptures. Of these migrating crabs, 19.3 percent were caught prior to September, while the majority of migrating crabs (56.1 percent) were caught during September to November, mostly along the mainstem of the Bay. Another 24.6 percent of migrating females were recaptured after November, mostly after they had already arrived in the lower Bay spawning area. Approximately half of the females migrated before mid-October, with approximately 36 percent caught before October 10 and 55 percent caught prior to October 23. Most migrating females were recaptured within one year of release, and only two crabs were recaptured more than 3 years after release, at estimated age 4.5-5 years. Most migrating females were recaptured along the shallow edges of the deeper tributaries (Potomac and York Rivers) and mainstem of the Bay. Most females (87 percent) migrating during September through November were caught in water shallower than approximately 30 ft (10 m). Recaptures for migrating females peaked at depths from 18 to 24 ft (6-8 m; 32 percent), and only 5 percent of females were caught deeper than 36 ft (12 m). Improved mechanistic understanding of migration, particularly spatial variation in the onset of migration and factors limiting the depth of migration, would help advise management of this intense fishery to ensure that quotas and stock preservation can be achieved effectively.