Constant harvest rate for the Pacific sardine (Sardinops caeruleus) fishery in the Gulf of California based on catchability-at-length estimations

Abstract

Constant harvest rate as a management strategy for the Pacific sardine (Sardinops caeruleus) fishery in the Gulf of California is supported by an analysis of variations in the catchability coefficient (q), stock abundance and commercial catch. Catchability was analyzed based on population length-structured data standard length (SL), expressed as CPUE, for 26 fishing seasons (1972-1973 to 1997-1998). We used a deterministic model of catchability to estimate the catchability-at-length assuming catchability depends on length and sardine behavior. Results demonstrated that catchability increases with sardine length, with low values for older sardines (sizes greater than 20.5 cm SL), which are poorly represented in catches. Most changes in q-at-length values can be observed within the range of 12.5-15.0 cm SL, which corresponded to first maturity and first capture lengths, respectively. Catchability-at-length pattern was represented for an exponential model with adjusted R2 = 0.94. Moreover, we observed an inverse power relationship between catchability and stock abundance with a slope value of [beta]d = -0.58, which indicates the existence of hyperstability or density-dependent catchability. The strong fluctuations in biomass of the Pacific sardine, the pattern of hyperstability, and the current state of the sardine fishery defined to be harvested at the maximum allowable catch, are the rationale for recommending a constant harvest rate as management strategy, with a value of HR = 0.29 and maintain the current minimum legal size of capture.