Determination of catchability-at-age for the Mexican Pacific shrimp fishery in the southern Gulf of California

Abstract

One of the main problems in the sequential Mexican-shrimp fisheries is the use of a constant catchability coefficient for fleets exploiting different population components implying a constant vulnerability in the population structure over time and age which denies important population processes and causes bias in fishery model outputs. The purpose of this study was to determine the catchability-at-age (qa,t)coefficients in time and across ages the sequential shrimp fishery fleets exploiting white, blue and brown shrimp in the southern Gulf of California. The qa,t values were able to identify the catchability patterns in time and across ages for each fleet, denoting important population processes (e.g. migration, recruitment and reproduction) per species. The qa,t values of the inshore fleet were three orders of magnitude lower than those from the offshore fleet in the white shrimp, showing an increase in the inshore fishing vulnerability which is associated to subadult migrations. The qa,tfor the offshore fleets were found to be of similar magnitude among species with the highest observed values in the brown shrimp. However, their patterns showed differential peaks of recruitment to the marine fishery and reproductive aggregations. For the blue and brown species, the increment in their vulnerability could be associated to the offshore fishery recruitment and the reproductive aggregations, observing an increase in the qa,t values in relation to the first maturity ages. The integration of the qa,t variability over time and across ages into the Mexican management of the shrimp fishery could improve the harvest rates and aid to reduce the growth and/or recruitment overfishing for the southern Gulf of California.