Environmental and fishery-driven dynamics of the common octopus (Octopus vulgaris) based on time-series analyses from leeward Algarve, southern Portugal

Dynamic factor analysis was used to explore monthly landings per unit effort (LPUE) series of Octopus vulgaris and environmental variables recorded in the southwest Iberian Peninsula, south Portugal. Despite the large fluctuations in the octopus abundance series, results showed a strong aggregation pattern for the last 3 months of the year, possibly related to the input of new recruits to the fishery. The calculated common trend for the 12 months time-series presented significant correlations with autumn rainfall of the previous year (lag 2 1), particularly for the October, November, and December series. Other important correlations were found for the Western Mediterranean Oscillation index (lag 2 1), Ekman transport, summer river run-off (lag 2 1), horizontal and vertical component of windstress, among others. The main trend describes a moderate steady increase in LPUE during the last 10 years, suggesting that octopus abundance has increased from 1990 to 2010. The strong correlations of the monthly octopus LPUE series, together with the annual life cycle, suggest that after environmentally controlled recruitment, population dynamics is largely fishery driven, resulting in strong seasonality in the landings.