The Role of Hydro-Climatic and Demographical Processes on the Spatio-Temporal Distribution of Cephalopods in the Western Mediterranean

Fluctuations in distribution of marine populations bring large implications in ecology and fisheries management. However, little is known about variability and factors influencing spatial dynamics in harvested groups other than fish. Using time series data from trawl surveys conducted in the western Mediterranean Sea (1994 - 2012), we analysed spatio-temporal distribution variability in terms of population displacements in latitude, longitude and depth of two cephalopod species with contrasting life histories, the nektobenthic squid Illex coindetii and the benthic octopus Eledone cirrhosa. We investigated the influence of demography (density, individual size) and environment (chlorophyll, runoff, precipitation, temperature, climate) to identify the drivers shaping cephalopods distribution in four shelf regions, including islands (local scale) and mainland (larger scale) areas with contrasting oceanographic and geographic conditions. Marked interannual fluctuations were found in the distribution of the two species. Distributions of both cephalopods were affected by the same variables, but their contribution depended on the species and regions. Different life strategies resulted in contrasting responses to environment, while I. coindetii associated to (spring) variables contemporary to surveys, E. cirrhosa was affected by previous winter conditions. The individual size mainly drove bathymetric changes, while chlorophyll, temperature or local climate revealed more important for geographical displacements.