Derivation of a Standardized Index to Explore Spatial, Seasonal and Between-Year Variation of Squid (Loligo Spp.) Abundance in the English Channel
2025
Marcout, Anna | Foucher, Eric | Pierce, Graham | Robin, Jean-paul
Long-finned squids are among the valuable resources exploited by English Channel demersal fisheries. This resource consists of two short-lived species (not distinguished in landings): Loligo forbesii and Loligo vulgaris, which differ in the timing of their life cycle. In the present study, we investigated spatial, seasonal and long-term biomass variation of Loligo spp. in the English Channel using 22 years (2000–2021) of commercial fishing data to compute biomass indices. Results indicated that landing per unit of effort (LPUE) indices (computed per month for each statistical rectangle of the English Channel), standardized by vector autoregressive spatio-temporal (VAST) method, provided an appropriate squid biomass estimator. Two distinct geographical patterns were observed in the English Channel, with low and stable biomass indices in the West and most of the fluctuations and seasonal variations in East. Within each year, the observed increase in abundance in June is likely to correspond to the recruitment of the loliginid squid into the fishery. Abundance typically rises from June to December and then gradually decreases from January to May. Over the 22-year series there has been an eastward shift in squid biomass since 2014. This information is valuable for fishers but also to manage fisheries, as it offers potential indices of squid availability to the fisheries and a direct quantification of loliginid biomass variability in the ecosystem.
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