Sex ratio variation in an exploited population of common octopus: ontogenic shifts and spatio-temporal dynamics

Abstract

Sex ratio is a fundamental demographic parameter with major implications for the dynamics, management, and conservation of animal populations. The objective was to study the main factors affecting the post-settlement population sex ratio (SR) of Octopus vulgaris off the NE Atlantic. We investigated the spatio-temporal dynamics in SR using more than 115,000 individual records obtained from onboard observers over a 14-year period. Generalized linear models were used to evaluate the abiotic and biotic factors affecting the variation in SR. The probability of catching a female decreased with size. Seasonal differences in SR resulted in a female-biased ratio in autumn and male dominance in summer. SR also varied along the bathymetric gradient with larger female proportion at deeper waters in winter and spring. The probability of catching a female was lower in hard substrates mainly in summer. Upwelling intensity and sea surface temperature did not show substantial effects on SR. The analysis neither revealed an influence of local density on SR. The spatio-temporal patterns of SR in O. vulgaris are likely based on differences in sexual behavior and life history which may affect catchability rates. Understanding the causes in SR patterns will provide valuable knowledge for future assessment and management plans