Seasonal variability of cephalopod populations: a spatio‐temporal approach in the Western Mediterranean Sea

Abstract

Cephalopod populations show wide temporal fluctuations in abundance, which have usually been investigated at inter‐annual scales related to environmental variability. However, cephalopods are also strongly linked to seasonal environmental fluctuations owing to their short life cycles and single seasonal breeding. Therefore, population abundance critically depends on the success of breeding and recruitment from the previous year and the optimization of resources in a narrow period of favorable conditions. This adaptation of population dynamics is paramount in marked oligotrophic systems, such as the western Mediterranean Sea. We used monthly landings per unit effort (LPUE) to explore the spatio‐temporal variability in seasonal patterns of three cephalopod species (Illex coindetii, Eledone cirrhosa and Octopus vulgaris). Common trends across the study area were characterized for each species. In all cases, seasonal patterns were geographically aggregated in relation to differences in local environment (i.e., primary production and surface hydro‐climatology). Variability in the mean seasonal pattern over time was also investigated under contrasting environmental or population regimes. The mean seasonal trend was more pronounced in regimes of high‐population densities, suggesting a density‐dependent control that can modify the strength of the environmental forcing in the seasonal patterns. Our study also evidences a spatial synchrony in the seasonal fluctuations of LPUEs. Scales of synchrony ranged from 70 to 200 km, indicating a patchy‐aggregated spatial pattern as a part of complex population structures in the western Mediterranean. Improving our understanding of seasonal dynamics of cephalopods across temporal and spatial scales may lead to improved forecasts and management strategies.

Accounting for ocean connectivity and hydroclimate in fish recruitment fluctuations within transboundary metapopulations

“…In the north-east, the spawning phenology of hake in the Ligurian and Thyrrenian seas is seasonally opposed to that in the Gulf of Lion, off the Iberian Peninsula and around the Balearic Islands, which occurs in autumn (Recasens et al 2008, Hidalgo et al 2009). Altogether, this allows us to simplify our metapopulation to six distinct eco-regions consistent with recent studies (Hidalgo et al 2009, Puerta et al 2016): Gulf of Lion, Catalan coast, Ebro delta, Valencia gulf, Northern and Southern Balearic Islands (Fig. 1).…”

“…, Puerta et al. ): Gulf of Lion, Catalan coast, Ebro delta, Valencia gulf, Northern and Southern Balearic Islands (Fig. ).…”

Environmentally driven synchronies of Mediterranean cephalopod populations

“…coindetii was bigger than that of O. vulgaris both around the Balearic Islands and off the Mediterranean coast of the Iberian Peninsula (Puerta et al, 2016b). Results are likely related to the fact that I. coindetii is an oceanic species with higher mobility and a wider home range (Roper et al, 2010).…”

“…General Linear Models (GLM) were applied to investigate the influence of environmental drivers on the abundance of the two objective species. Sea surface temperature (SST) and chlorophyll a concentration (Chla) were used as putative drivers owing to their significant effects on cephalopod populations (Keller et al, 2014;Pierce et al, 2008b;Puerta et al, 2016b). Chla and SST data resulted from MODIS-Aqua and NPP-VIIRS sensors measurements already processed with regional ocean colour algorithms (resolution 1 km, daily data) and were downloaded from the MyOcean database Cephalopod abundances (response variable) were modelled using the following explanatory variables: SST, Chla, year and GSA.…”

“…Among the environmental parameters investigated until now, sea surface temperature (SST) plays an important role in driving cephalopod abundance trends (Zuur and Pierce, 2004;Chen, 2010). Additionally, a recent study investigated local scale seasonal synchronies in Mediterranean cephalopod abundances (Puerta et al, 2016b), revealing contrasting seasonal cycles in response to local environmental conditions. Due to the decline in the traditional finfish resources, European cephalopod fisheries, which were once located mostly in the Mediterranean, have grown and expanded northwards (Pierce et al, 2010).…”