Publication Abstract

Environmental and stock effects on recruitment variability in the English Channel squid Loligo forbesi

L. Challier , J. Royer , G.J. Pierce, N. Bailey, B.A. Roel and J.P. Robin

Recruitment variability is commonly attributed, inter alia, to variation in spawning stock size and environmental variability. Here, population estimates were quantified from re-examined and updated stock assessments of the English Channel Loligo forbesi stock. Environmental and adult biomass effects were then tested on recruitment variation. A stochastic length-age key of L. forbesi in the English Channel was included in cohort analysis, considering inter-individual variability in age at length. The number of recruits and parental stock biomass per monthly age-class were computed for a series of 13 fishing seasons (1989-2002). Recruitment was examined in relationship to adult biomass and/or environmental parameters (sea surface temperature, SST, and the North Atlantic Oscillation, NAO) at the time of hatching. Recruits were 7 month old and recruitment for each annual cohort occurred between April and August. The spawner biomass was simplistically taken as squids bigger than the length at maturity. In the spawning season (September December), spawners included 11-13 month old animals. Parametric stock-recruitment curves (Ricker, Beverton and Holt, Shepherd,…) fitted weakly, while SST was negatively correlated with recruitment in a simple linear model. The NAO-recruitment time-series failed to reveal a significant relationship. A model combining SST and adult biomass showed that recruitment is probably density-dependent when stock size is high, and negatively correlated with temperature. The study did not indicate obvious recruitment overfishing of the English Channel L. forbesi population.

Reference:

L. Challier , J. Royer , G.J. Pierce, N. Bailey, B.A. Roel and J.P. Robin (2005) Environmental and stock effects on recruitment variability in the English Channel squid Loligo forbesi. Aquatic Living Resources, 18(4): 353-360