Spatial Allocation of Shrimp Catch Based on Fishing Effort: Adjusting for the Effects of the Texas Opening

Abstract

Estimates of fishing effort for the Gulf of Mexico penaeid shrimp fishery depend on the ability of National Marine Fisheries Service port agents to accurately assign fractional catches within a fishing trip to 5-fathom-depth bins within 21 Gulf of Mexico statistical areas. In previous studies, we showed that the method used for assigning landings was inaccurate and developed an algorithm for assigning landings based up observer and captain's logbook data on fishing effort and catch. The resulting algorithm explained over 92% of the variance in actual catch. Results of regression analyses of new observer data collected for over 7,700 tows confirm that the algorithm provides reliable estimates of fractional catches associated with the different subareas fished within a trip (adjusted r ² = 0.96 when 11 outliers are removed from 1,845 observations). Nine of the 11 outliers occurred within a month of the Texas opening, a period when catches are initially high but then decay rapidly. Here, we have incorporated this decay as part of the allocation algorithm for this period. The agreement of expected and actual shrimp catch declined slightly from the regression with outliers removed (adjusted r ² = 0.95). Nevertheless, we suggest that data from this period should be modeled separately to better evaluate the consequences of management actions that might be taken during the Texas opening time frame.