Heavy fishery exploitation does not affect sizes at recruitment and maturity of squid Illex argentinus and Doryteuthis gahi, in the Southwest Atlantic

Abstract

Abstract Commercial exploitation often impacts the life-history parameters of iteroparous and semelparous fishes, and prolonged fishing pressure may lead to fisheries-induced evolution. However, information is lacking on how fishing exploitation affects short-lived semelparous cephalopods. This study examines the impact of heavy commercial fishing on Illex argentinus and Doryteuthis gahi, two annual squid species around the Falkland Islands in the Southwest Atlantic. Changes in two life-history parameters; size at recruitment and size at maturity, were standardized for sea temperature and analysed in relation to relative biomass indices over 34 years for I. argentinus and 31 years for D. gahi. For both squid species, correlations of these life-history parameters were observed with biomass and temperature, but size at recruitment and size at maturity did not change significantly over the extended periods of their commercial exploitation. Sizes at recruitment and maturity of these short-lived squid appear to remain stable in absence of size selection in their respective fisheries. Both jigs and trawls capture the entire size ranges of squid recruited to the fishing grounds, thus avoiding direct fisheries-induced selection on their size-dependent life-history parameters. With only one cohort/generation at a time present during growth-phase fishery, both squid species studied seem to be more resilient to fisheries-induced changes in sizes at recruitment and maturity than short-lived semelparous fish and squid subjected to terminal fisheries. Instead, these size-dependent life-history traits of squid fished during their growth phase are mainly driven by short-term changes in population density and environment, including ambient temperature.