A Model for Predicting Commercial Fishing Effort for Blue Crab in Chesapeake Bay Tributaries

The spatial and temporal dynamics of fishing effort in small scale artisanal fisheries may be difficult to understand because of inadequate self-reporting systems and because effort may respond to socio-economic and environmental variability.  In the Maryland portion of the Chesapeake Bay’s tributaries, commercial fisheries for the blue crab (Callinectes sapidus) are restricted to the use of baited trotlines, which are deployed from small fishing vessels (4-12m).  A randomized, boat-based, roving survey was designed and used to quantify fishing effort in two tributaries of the Chesapeake Bay (Patuxent and Wye Rivers) over two years.  These systems represent a range of characteristics that are found in Chesapeake Bay tributaries in terms of geomorphology, geography, freshwater input, and average size of fishing vessel utilized.  The survey used a progressive count method to estimate the number of fishers.  The survey was repeated on each sampling day in order to quantify fishing effort using a retrospectively estimated decay function derived from the difference in count of fishers from each survey replicate.  A general linear model was developed to understand the role of weather (wind speed, precipitation, temperature), water temperature, month, day of the week, Julian day, tributary surface area, and proximity to holidays (periods of high demand for crabs) as a function of fishing effort in each tributary.  A total of 4,393 commercial crabbers were encountered during the survey.  July and August had the highest level of fishing effort, and effort levels were generally correlated with water temperatures across the fishing season.  Thursdays, Fridays, and Saturdays saw the highest fishing effort and sampling near holidays (Independence Day and Labor Day) revealed significant increases in effort.  Results from our model suggest that fishing effort may be predicted by meteorological, oceanographic and temporal variables after accounting for restrictions placed on the fishery by the state management agency. Our survey and corresponding model provide new insight for fisheries managers attempting to account for the variability of fishing effort for blue crab in Chesapeake Bay tributaries.