Results in Context

Findings from the Winter Blue Crab Dredge Survey 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. During this period
  • spawning stock declined by 81%
  • female size declined by 8%
  • spawning stock biomass declined by 84%
  • mean size at maturity diminished by 9%

In addition, larval abundance and post-larval recruitment were lower by approximately an order of magnitude compared with earlier years.

The initial decline resulted from poor recruitment in 1991, despite high spawning stock and larval abundance. This recruitment failure, in concert with high fishing pressure and natural mortality, led to a diminished spawning stock in 1992 and thereafter.

The Bay’s blue crab population has experienced numerous “boom and bust” cycles in the past, due to natural environmental variability and year-to-year differences in recruitment success. What was particularly troubling about the 1992-2007 decline was that it persisted for more than a decade. The decline also occurred rapidly, within 1 to 2 years, indicating a “phase shift” rather than a progressive decrease.

Prognosis

The spawning stock and larval abundance of blue crabs in Chesapeake Bay rebounded beginning in 2008 due to management actions that included a blue crab spawning sanctuary and harvest restrictions. However, the stock experienced another sharp drop in 2013-14. The baywide population is unlikely to persist at high levels without significant reductions in natural mortality, along with enhanced environmental conditions conducive to successful recruitment. The key consequences of a smaller spawning stock and poor recruitment are an increased likelihood of recruitment failure and reduced resilience to environmental setbacks such as cold snaps or tropical storms.

The demonstration of a concurrent decrease and significant association between spawning stock abundance and recruitment, larval abundance, and female size is characteristic of blue crabs and of marine invertebrates in general, and indicates an urgent need to conserve the spawning stock for long-term sustainable exploitation and population persistence.