Analysis of the Vigo-Marín bottom trawl fleet operating in ICES Division VII for possible standardization

Abstract

In order to consider the possible standardization of the cpue of the Vigo-Marín trawl fleet operating in ICES Division VII for its potential use as an abundance index for the assessments of the stocks of megrim (Lepidorhombus whiffiagonis) and anglerfish (Lophius piscatorius and L. budegassa) in ICES Divisions VIIb–k and VIIIabd, a series of preliminary analyses were conducted on data collected on both landings and discards historic time-series. This document complements the work conducted in Fernández et al. (2008). Updated information through to 2010 is now available, which is taken into consideration. At the same time, the present document considers the main species caught by this fleet (L. whiffiagonis, L. boscii, L. budegassa, L. piscatorius, Merluccius merluccius and Nephrops norvegicus) in order to try to ascertain whether possible changes in the directionality of the fleet may have occurred over time. There does not seem to be a clear change in species composition through the time-series analysed (1986–2010) but an increase in cpue for most species could be observed in approximately the last decade. Qualitative information from the fishing industry confirms that cpues have increased in the last decade and notes the fact that this fleet was substantially renovated during the 1990s, which may well have led to an increase in its efficiency. For megrim (L. whiffiagonis), the information examined by Fernández et al. (2008) and further extensions considered in this work suggests that the strong increase in cpue from 1999 onwards is more likely due to the technological improvement mentioned above rather than to a strong increase in stock abundance. Thus, the recommendation made by Fernández et al. (2008) that if this cpue series were to be used for tuning the megrim assessment, it should better be split in two periods, one covering from 1984 to 1998 and another one from 1999 onwards, still seems appropriate.