Gulf of Mexico shrimp stock assessment workshop.




Nance, J.M.
Klima, E.F.
Czapla, T.E.

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The present statistical survey attempts to account for all commercial landing through a daily to weekly canvass of precessing plants. From dealers' receipts, port agents transcribe the details of landings for each vessel trip. Most dealers are familiar with the species compositions of shrimp landed since shrimp are sold as white, brown, or pink (i.e., Penaeus setiferus, P. aztecus and P duorarum respectively). A breakdown by species for each landing is then obtained automatically when transcribing landing data from dealer records. Size composition of the landings is recorded as number of tails per pound (count). Before 1984, values greater than 67 count were considered as a single category. Since that time, specific size information has been detailed into whatever market categories were recorded by the dealers. Fishermen are interviewed by port agents to determine effort expended and location of specific catches. To facilitate geographical assignment of commercial trawling effort and shrimp catch, the U.S. continental shelf of the Gulf of Mexico has been subdivided coastwide into 21 statistical subareas. These areas have been further subdivided into five fathom increments of depth from the shoreline out to the edge of the continental shelf. Fishery statistics information is reported by these areal divisions hereafter termed location cells. Total monthly effort for each species is estimated from the interview records. To estimate effort directed at a single species, only interviews in which at least 95% of the catch was a single shrimp species are used for calculation of catch per unit of effort (CPUE). An average CPUE directed at a single species is calculated for each location cell. Most cells (about 85-95%) have a CPUE based upon interview data. Nichols (1984) outlines the methodologies used to calculate CPUE values for cells that have catch but no estimate of effort. Once a CPUE is calculated for each cell for each month on a species by species basis, effort can be calculated for the cell-month-species array. Directed effort in a given location is simply calculated by dividing the catch by the CPUE. It must be remembered that the values for directed effort are not necessarily additive across species.


41 p.


shrimp fisheries, penaeid shrimp, abundance, fishery resources, resource management, fishery management, stocking, shrimp