About Blue Crabs
For decades blue crab harvests have risen and fallen, most likely in concert with climate and other factors we still do not fully understand. Since the 1990s, however, concern has grown that pressure on the blue crab — both commercial and recreational — may be too high. State agencies such as the Maryland Department of Natural Resources and the Virginia Marine Resources Commission, along with bi-state groups such as the Bi-State Blue Crab Advisory Committee and the Chesapeake Bay Stock Assessment Committee, have focused their efforts on trying to understand the current status of Bay blue crab stocks, and to what degree they may be in danger of overexploitation.
See Chesapeake Quarterly, Counting Blue Crabs in Winter. Also see Maryland Marine Notes The Bottomline on Blue Crabs: Setting Thresholds for the Last Great Fishery.
In addition to questions about commercial and recreational catch are concerns about Bay water quality, and crab habitat in particular. Of special concern are the nutrients that have fueled algal blooms and shaded the Bay's underwater grasses. The grass beds that remain in the Chesapeake are only a remnant of what once covered the Bay floor (see Maryland Marine Notes Restoring Bay Grasses: A Long Way Back). As many watermen have pointed out, until Bay water quality improves, bringing back underwater grasses and increasing oxygen levels, the blue crab will not likely thrive.
Protecting crab habitat can take varying forms. In Virginia, for example, researchers and resource managers have helped to establish a deep-water sanctuary, which will help protect spawning females in waters deeper than 35 feet, from June through September. Such corridors should help assure that not every area of the Bay risks over-exploitation, but careful research and monitoring will be needed to analyze their effectiveness. For other management options, see Managing Crabs.
Scientists in the Bay region have studied crabs for many decades. Long-term trawls undertaken in Maryland and Virginia, some dating back to the 1950s, have provided a useful picture of how crab stocks have changed over time. Since 1990, a particularly important Baywide monitoring of crabs called the "winter dredge survey" has tracked crab stocks by sampling during the winter, when crabs bury themselves in the Bay bottom. Though many questions remain about the blue crab's biology and life span, there are many things we now understand thanks to scientific inquiry. Research such as that undertaken by during the late 1970s and early 80s, by Steven Sulkin and his colleagues, for example, described the behavior of crab larvae that first brings them to the surface to flow seaward, and later brings them back down to the bottom, where heavy saline currents return them to the Bay. More recently, work has continued to describe the reproductive dynamic of the blue crab, charting population changes, as well as the influence of important habitat such as grass beds and important predator-prey relationships.
The Maryland Sea Grant College is currently preparing a book on the blue crab that will summarize the scientific knowledge of the crab. It will be available in early 2007.
Blue Crab Ecology
To track crab research now underway by Dr. Tom Miller, University of Maryland Center for Environmental Science Chesapeake Biological Laboratory, visit his web site entitled Chesapeake Bay Blue Crab Assessment 2005. Also visit the research sites listed on the Crab Links page.