On the interdependence of sequential fisheries: The brown shrimp, Farfantepenaeus aztecus, fisheries in the northwestern Gulf of Mexico

This contribution deals with some aspects of sequential shrimp fisheries, particularly the relation between survival after catch in inshore waters and recruitment to the offshore fishery. This relation is described for the brown shrimp, Farfantepenaeus aztecus, in the northwestern Gulf of Mexico, using a modified catch equation, the solution of which is approached using catch data, with a delay between catch-at-migration time (inshore waters) and recruitment to the offshore fishery. Recruitment decreases as a logarithmic function of catch, the form of which is defined fishing mortality and migration rate. For a period of 8 years of monthly data, the explained variance of recruitment at the offshore fishery was more than 60%, but for the average pattern it increases to 80%. The main concept behind this model is to identify a desirable survival level in inshore waters after catch, that permits a number of recruits to the offshore fishery to maintain stable yields. The model described above was unable to be directly used for management purposes, because of a large variance along the catch axis. The second derivative of the model was used to represent increments in survival rate (to offshore fishery) as a function of inshore catch. Several tendencies were explored, but inshore catch that stabilizes survival is tentatively suggested as the more appropriate to be used as a criterion for management. In practice, the desired survival level can be approached monitoring fishing in inshore waters.