Population structure and reproductive dynamics of Octopus insularis (Cephalopoda: Octopodidae) in a coastal reef environment along northeastern Brazil

Abstract

Octopus insularis is the most important octopus commercially fished in northeastern Brazil. Its reproductive dynamics were studied in order to contribute to the biological basis for its management along Rio do Fogo, a small community in a partially protected marine area in northeastern Brazil. Overall, 1108 specimens were caught by the free diving fishery and experimental pot fishery, down to 15m depths between November 2009 and September 2011. These specimens had their mantle length (ML) and body weight (BW) recorded. The gonads of 545 specimens were examined. The overall sex ratio did not differ from 1:1, but males were more frequent in the smaller ML classes whereas females were more frequent at over 90mm ML. The ML (ML50) and weight (W50) at maturity were estimated to be 60.0mm and 215.2g in males, and 95.2mm and 493.7g in females. The peaks of maturation lasted for approximately three months and occurred at intervals of 7–10 months. Mean ML and gonadossomatic indices were strongly correlated with cycles of sea surface temperature and wind intensity. Octopods in all maturity stages were observed throughout the year; however, mature females were scarce, suggesting that they might migrate to spawn in deeper waters. Based on this study it is recommended that a minimum allowed catch size measure of around 500g is implemented in the fishery in order to avoid catching both small mature males and maturing females, and that octopus fishing is restricted to depths of up to 15m to avoid fishing mature spawning females. These restrictions could contribute to the sustainable exploitation of this stock that yields several hundred tons of octopuses each year.