Do some like it hot? Temperature as a possible determinant of variability in the growth of the Patagonian squid, Loligo gahi (Cephalopoda: Loliginidae)
Loligo gahi were collected from bottom trawl samples taken around the Falkland Islands on both commercial and research vessels from January 1994 to November 1995. Commercial samples were taken from both seasons of the fishery (February–May, August–October), research samples were taken in January, June and November. A sub-sample of squid was taken from each sample to provide statoliths for age determination by statolith increment analysis. Sea surface temperature data were derived for an area encompassing the southerly portion of the fishing grounds for L. gahi to provide an indicator of seasonal temperature variations for that region. Age data were derived for 486 females and 445 males. Exponential and power growth models explained the fit to the size-at-age data to a similar extent. Age data were grouped by month and by season of hatch to test the hypothesis that seasonal temperature variability influences the size-at-age relationship in L. gahi. Analyses of covariance showed that the relationships of both predicted mean mantle length and predicted mean body mass per month of hatch, and per season of hatch resembled closely the trends in mean monthly sea surface temperature, with the squid hatched in the summer, i.e., at higher temperatures, being significantly larger than squid of the same age but hatched in the winter months. The growth rates for adult squid in this study were similar over the age range analysed. This study provides evidence that increased temperature during a squid’s early growth period may accelerate growth markedly giving rise to significant differences in size-at-age for adult squid hatched at different temperatures.