Octopus life history relative to age, in a multi-geared developmental fishery

The ability to obtain broad-scale age information for an exploited octopus population enables the identification of essential life history information, such as age at maturity, recruitment pulses and seasonal effects on growth. This study uses stylet weight (reduced internal shell) as a proxy to age 3494 Octopus (cf) tetricus, the target species of a rapidly developing octopus fishery in Western Australia. Samples were collected during 2008-2012 using passive shelter pots and active trigger traps. Both males and females were found to have similar maximum ages at 1.5 years, with males reaching maturity at 243 days compared to 379 days for females. The two gear types selected for different parts of the population, with shelter pots catching mostly octopus <1 kg total weight, who were a mixture of immature females and immature/mature males, whereas trigger traps caught octopus >1 kg total weight, of which 75% of the total catch were mature males. This variation in catch composition coupled with the inshore (shelter pot) and offshore (trigger trap) depth profiles of the gear types suggests offshore migration may be occurring. Back-calculated hatch months revealed six-monthly recruitment pulses and a positive relationship with ascending sea surface temperature and growth up to 22 °C.