Crab population dynamics

Reseach at QuaFEL on the population dynamics of blue crab has taken two main thrusts: stage-based population models and stock assessment activities. The stage based modeling conducted since 1997, with support from Maryland Sea Grant, has sought to identify stages and vital rates that potentially regulatie the crab population in Chesapeake Bay. Initial model development assumed density -independent conditions and took advantage of the suite of analytical tools that are available for such models (e.g. elasticity analysis). This work lead to the publication of two papers. Miller (2001) showed that exploitation rates then occuring in the Chesapeake Bay blue crab fishery were likely too high. Egg production by large adult crabs was indicated as a regulatory stage in the population dynamics. Results indicated that closure of the winter dredge fishery in Virginia would contribute to increased sustainability, but would not by itself guarantee sustainability. In a subsequent spatial extension of this model , Miller (2003) showed that variation in zoeal survival was not likely to be a controlling factor the population. This work is currently ongoing and involves the development of density-dependent versions of the original stage-based matrix format.

Paralleling this basic research into crab population dynamics, QuaFEL has also been involved in stock assessment activities for blue crab in the Chesapeake Bay. Following an initial report that identified the needs for targets and thresholds for the blue crab fishery, Miller was part of a multidisciplinary team that implemented targets and thresholds for the Chesapeake Bay (Miller et al. 2001). These recommendations were acted on by regional management agencies and lead to a policies desinged to reduce fishing mortality rates by 15% in 2003. In 2004/5 QuaFEL staff lead the team to update the original Rugolo et al. assessment. This work was completed in 2005, and independently reviewed by international experts. The principals developments in this assessment were a revised approach to estimating natural mortality rates, statistical approaches to correct for reporting changes in landings, development of a new stock assessment methodology, and a revised set of management rules for the fishery. The assessment concluded that the population is at a low level of abundance, but that the fishing pressure while above the target rate, is likely below the threshold. The full assessment is available by clicking here.

Last revised: 6/29/2007