Gillnet Mesh Selectivity for the Shovelnose Guitarfish (Rhinobatos productus) from Fishery-Dependent Data in the Artisanal Ray Fishery of the Gulf of California, Mexico

The Gulf of California supports the largest ray fishery in Mexico. Sonora is a major ray-fishing state, reporting 56 % (live weight) of the Pacific Ocean rays production. Bottom-set gillnets are the principal fishing gear deployed in this artisanal fishery. In the absence of long-term monitoring and complex biological data for fishery stock assessment, an understanding of the selectivity properties of gillnets can provide a basis for implementation of a standard mesh-size as regulation tool for fishery management. Ideally, gillnet selectivity parameters are determined from fishing trials with several gillnets of a range of mesh-sizes constructed and used in a way to control for factors likely to affect the fishing power nets. In the absence of such experimental data, the present study uses available fishery-dependent monitoring data standardized to construct a data set that meets as near as possible the conditions met in a controlled experiment. A likelihood-based method was used to estimate the selectivity parameters for the shovelnose guitarfish (Rhinobatos productus) caught in the Gulf of California. The values of the selectivity parameters were θ1 = 105.7 and θ2 = 21 741 for 3.5, 5, 6, 8, and 8.5 inch mesh sizes. Key words: artisanal fisheries, elasmobranchs, gear selectivity, gillnet, rays, regulatio