Application of generalized linear modeling to catch rate analysis of Western Mediterranean fisheries: the Castellón trawl fleet as a case study

Abstract

Generalized linear modeling (GLM) is used to analyze hake catch rates in the Spanish trawl fleet fishing off Castellón (E Iberian Peninsula) between 1991 and 1996 and to provide consistent indices of abundance. Main effects in the models include a factor for vessel tonnage, to adjust for characteristics that determine fishing power, as well as factors for year, month and fishing closure. Vessel tonnage, season and year are shown to have a significant effect on hake catch rates, with vessel capacity alone explaining about 54% of the total variation in the data. Significant interactions indicate that monthly fluctuations in catch rates differed by year probably in relation to the timing of hake recruitment and of the bimonthly annual closure of the fishery. Hake abundance indices, as derived from the year coefficients in the model, were intermediate in 1991 and 1992, low in 1994 and 1995 and high in 1993 and 1996. This result is corroborated by abundance indices from survey estimates for the later years. The model explains 63% of the variation in the CPUE data, which is similar or above of what has been found by other authors in comparable studies for fisheries around the world. Thus, the modeling approach of catch rates from trawl fisheries offers a promising method for obtaining standardized abundance indices of groundfish stocks in the Western Mediterranean. Further application is the study of area effects on catch rates of fleets sharing the same resource in the region.