Evaluation of the Chesapeake Bay blue crab sanctuary through habitat suitability

ABSTRACT: Dynamic fisheries management requires continual evaluation of management strategies. Despite the implementation of various spatiotemporal harvest and gear restrictions over the past 2 decades, the Chesapeake Bay blue crab Callinectes sapidus population has not responded consistently. To determine whether environmental factors may be impacting the efficacy of a seasonal blue crab sanctuary, a generalized additive modeling approach was applied to long-term (2002-2018) bottom trawl survey data to develop an ecological niche model (ENM) for mature female blue crabs in the mainstem of the Bay throughout the primary spawning season (May-September). Salinity, temperature, dissolved oxygen, depth, and sediment type were significant predictors of crab relative abundance. The ENM was then coupled with hindcast estimates of environmental covariates from a high-resolution hydrodynamic-biogeochemical model to develop habitat suitability indices (HSIs). This habitat-based approach was compared with a model-based index of abundance and a species distribution model (SDM). HSI and the model-based index were generally similar, exhibiting no clear trends through time, though variability was lower in the HSI. Clear seasonal patterns in spatial distribution were evident, with highest relative abundances occurring in the lower bay in July and September, corresponding to the movement of females towards higher-salinity waters to spawn. The sanctuary protected 46-59% of the good mainstem habitat each year and generally overperformed in years when bay-wide HSI was low. These results contribute to our knowledge of mature female blue crab ecology during migration and spawning and provide further support for the importance of the sanctuary for mature female blue crabs.