Reproductive activity of the tropical arrow squid Doryteuthis pleiaround São Sebastião Island (SE Brazil) based on a 10-year fisheries monitoring

Abstract

Monthly samples of Doryteuthis plei were obtained from the small-scale hand-jigging fishery aroundSão Sebastião Island (24◦S), Brazil, across seven fishing seasons (November–April) during the period2002–2012, with the aim of identifying the exploited population patterns with emphasis on thereproductive activity. In order to explore the process of development of reproductive organs, the size-at-maturity, and the spatial–temporal factors explaining maturation, an analysis of the sex-ratio, maturity,gonado-somatic index (GSI), concentration of spermatophores, biometric relationships, and two GAMLSS(Generalized Additive Model for Location Scale and Shape) was applied. D. plei recruited to local fisheriesat around 161 mm mantle length (ML), males being, on average, 1.6 times larger than females. Femalesappeared more frequently during the first three months of the fishing season while males tended to bemore frequent at the end of the season, confirming the existence of female post-spawning mortality. Thepresence of high proportions of mature squid was found throughout the fishing seasons for both sexes.The size-at-maturity was estimated at 143.3 mm ML in females, and 210 mm ML, in males. Both sta-tistical models indicated robust non-linear correlation between gonad weight, biometric variables, andspatial–temporal factors (p < 0.001). Ovary weight mostly correlated with accessory glands weight, whiletestis weight correlated with ML. In both sexes, depth was found to be a significant variable explainingmaturation, with higher gonads weight between 15 m and 20 m, and especially in the island’s South andSoutheastern areas. Statistical models also evidenced a significant peak of gonad weight in February andMarch, for females, and in March, for males. Inter-annual variation showed a peak of gonad weight inthe fishing season 2011–2012. Overall, findings based on long-term monitoring should assist resourcemanagement (e.g. for seasonal, size, and spawning area protection) which seems potentially valuable forlong-term sustainability of local fishing communities.