Virginia Institute of Marine Science

Winter Dredge Survey

The Bay-wide Blue Crab Winter Dredge Survey (WSD) is an annual cooperative effort between the Virginia Institute of Marine Science (VIMS) and the Fisheries Service of the Maryland Department of Natural Resources (DNR).

The survey, in operation since 1990, allows researchers to

  • Accurately gauge the total population of blue crabs in Chesapeake Bay
  • Identify year-to-year trends in blue crab abundance
  • Characterize the size and sex of individual crabs
  • Estimate over-wintering mortality
  • Understand seasonal migration patterns, and
  • Assess the effects of the crab harvest

The winter dredge survey is the most comprehensive and statistically sound of the blue-crab surveys conducted in the Bay. The Virginia Marine Resources Commission and other resource management agencies rely on its findings, along with data on annual fishery removals, to guide their on-going management of Chesapeake Bay’s blue crab stock.

Survey results show that there was a persistent and substantial decline in the spawning stock, recruitment, larval abundance, and female size of blue crabs in Chesapeake Bay between 1992 and 2007. However, management actions initiated in 2008—including a blue crab spawning sanctuary and harvest restrictions—are now helping the Bay’s blue crab population rebound toward a healthy, sustainable level.

Results from the most recent Winter Blue Crab Dredge Survey show  a mixed bag of good and not-so-good news that may result in a slight tightening of commercial harvest restrictions. Results of the 2012 baywide survey reveal that the overall abundance of blue crabs dropped precipitously, from 765 million to 300 million crabs. This was because the number of juvenile crabs plummeted from 581 million to a mere 111 million. However, the number of spawning-age females increased substantially, from 95 million to 147 million, and remains well above the scientifically-established, healthy-abundance threshold of 70 million.