Estimating a population of pink shrimp by the use of catch per effort and tagging data

A study of some methods used to obtain information on the dynamics of the Tortugas pink shrimp (penaeus duorarua) fishery in south Florida is given. Tagging experiments were used together with catch and effort data to find population seize, fishing mortality, immigration, and a combined figure for omigration and natural mortality. Since the data employed were inadequate in some respects for an accurate population estimate, the emphasis of the study was placed on the examination of methods used rather than the actual answers obtained. The fishing success (DeLury) method was used concurrently on both tagged and untagged shrimp populations. This method involves the study of catchability curves which represent the relationship of the catch per effort to the accumulated catch and permits estimates of population size. The Peterson method was used to determine population size simultaneously with the fishing-success method to provide a partial check on the results. The total catch of the fishery was obtained from all dealers on a daily basis and a daily sample of the vessels making landings was interviewed to estimate daily fishing effort. Because the number of interviews collected was low on some days, an effort was made to strengthen these data by relating nights fished to average daily wind velocity. This permitted the use of all interviews obtained for any wind velocity to be totaled to calculate fishing effort for any day. During one period, January 12 to March 15, 1958, the catchability curve was convex and suggested that omigration and natural mortality were not balanced by immigration or that the gear efficiency had changed during the period.