Biology of a re-emerging population of octopus from north-eastern Atlantic

The sudden development of the common octopus ( Octopus vulgaris ) population in southern Brittany (France, north-east Atlantic), and its subsequent exploitation by local fisheries, made it necessary to assess the biology of this population. Body weight, ventral mantle length, gonad maturity, age and hatching season were estimated on individuals caught by fishermen during one year and a half. The occurrence of hatching throughout the year, together with the presence of mature females from November to July, suggests year-round reproduction. However, the higher proportions of mature females observed between March and June indicate that octopuses preferentially reproduce during spring. The relationship between age and body weight suggests that octopuses from southern Brittany exhibit a slower growth than those in previously investigated regions. Faster growth was also observed in individuals that hatched in summer compared to those hatched in winter. Inter- and intra-regional growth plasticity was hypothesised to result from the influence of temperature on life history traits. • Application of biometry, maturity and age data for a wild octopus population. • Identification of one preferred reproduction period. • Inter- and intra-regional plasticity in growth explained by temperature.