An Evaluation of the Synchronization of Blue Crab Populations Along the Atlantic Coast Using Landings and Survey Data

Spatial synchronization of two or more distinct populations due to regional environmental conditions, termed the Moran effect, has been observed for a wide range of species and ecosystems.  Mechanisms behind synchronization in marine environments are difficult to identify because of the vastness of the ocean and complex life histories of oceanic species.  Blue crabs exhibit a complex life history with high mixing potential as larvae and negligible migration between estuaries as adults.  The species also supports important commercial fisheries in many states throughout its range.  Over the past two decades there have been declines in landings and survey indices for many blue crab populations along the Atlantic coast.  Here we use fishery-dependent landings data and fishery-independent survey data from Florida to New York to parameterize catch-survey models to estimate a time series of absolute abundance estimates for each state.  These time series were then analyzed to assess the degree of coherence in abundance among blue crab populations and to explore possible mechanisms driving synchronization.  Principal component analysis was used to examine the patterns of spatial synchrony of fluctuations in landings.  Dynamic factor analysis was used to assess temporal patterns in synchrony, as well as to determine if any environmental variables, including the North Atlantic Oscillation, water temperature, and sunspot number, could explain a portion of the patterns observed.  Understanding the mechanisms behind population fluctuations would be valuable for the sustainable management of both the fisheries and the ecosystems in which these populations occur.