Sex ratio variation in an exploited population of common octopus: ontogenic shifts and spatio-temporal dynamics
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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.
KeywordsSex ratio Life history Fisheries Octopus vulgaris NE Atlantic
This study is indebted with all the onboard observers that carried out the sampling, and with the UTPB that runs the monitoring program of the artisanal fishery sector in Galician waters. Many thanks to David Villegas-Ríos for reviewing the manuscript and providing general advice and fruitful discussions. This study was financed by the research project CASGASS (http://www.ices.dk/community/icessciencefund/Pages/default.aspx) under the ICES Science Fund program (2014), and also by the Agreement between CSIC and Xunta de Galicia to analyze fisheries-dependent data from the monitoring program of small-scale fisheries in Galicia (Agreement No. 070401150009). Jaime Otero was supported by a “Junta para la Ampliación de Estudios” Fellowship (JAE-Doc programme 2011) from the CSIC and ESF.
Compliance with Ethical Standards
Conflict of interest
The authors declare that they have no conflict of interest and consent was obtained from all participants of the study.
All the animals have been sampled from regular operations of the artisanal fishery under the regional monitoring program of the fishing activity.
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