Appendix A. Additional figures on cokriging results: empirical and fitted variograms, histogram of all the standard errors of the cokriged estimates of the tuna presence, and values of index of presence for two coefficients of intensive search (IS) parameter.

Additional figures on cokriging results: empirical and fitted variograms, histogram of all the standard errors of the cokriged estimates of the tuna presence, and values of index of presence for two coefficients of intensive search (IS) parameter

Spatio-Temporal Patterns of Key Exploited Marine Species in the Northwestern Mediterranean Sea

<div><p>This study analyzes the temporal variability/stability of the spatial distributions of key exploited species in the Gulf of Lions (Northwestern Mediterranean Sea). To do so, we analyzed data from the MEDITS bottom-trawl scientific surveys from 1994 to 2010 at 66 fixed stations and selected 12 key exploited species. We proposed a geostatistical approach to handle zero-inflated and non-stationary distributions and to test for the temporal stability of the spatial structures. Empirical Orthogonal Functions and other descriptors were then applied to investigate the temporal persistence and the characteristics of the spatial patterns. The spatial structure of the distribution (i.e. the pattern of spatial autocorrelation) of the 12 key species studied remained highly stable over the time period sampled. The spatial distributions of all species obtained through kriging also appeared to be stable over time, while each species displayed a specific spatial distribution. Furthermore, adults were generally more densely concentrated than juveniles and occupied areas included in the distribution of juveniles. Despite the strong persistence of spatial distributions, we also observed that the area occupied by each species was correlated to its abundance: the more abundant the species, the larger the occupation area. Such a result tends to support MacCall's basin theory, according to which density-dependence responses would drive the expansion of those 12 key species in the Gulf of Lions. Further analyses showed that these species never saturated their habitats, suggesting that they are below their carrying capacity; an assumption in agreement with the overexploitation of several of these species. Finally, the stability of their spatial distributions over time and their potential ability to diffuse outside their main habitats give support to Marine Protected Areas as a potential pertinent management tool.</p> </div

Juvenile <i>versus</i> adult stages comparison.

<p>Average maps (1994–2010) of the log-density (Z) of juveniles and adults of the European hake (<i>Merluccius merluccius</i>) and the small-spotted catshark (<i>Scyliorhinus canicula</i>). In the first column the corresponding variograms are displayed.</p

Study area and sampling sites.

<p>Map of the Gulf of Lions and the 66 sampling sites (identified by a red point) during the whole MEDITS survey (1994–2010). The positions of the sites were fixed by a stratified sampling scheme.</p

Annual maps of red gurnard.

<p>Kriged annual maps of red gurnard (<i>Aspitrigla cuculus</i>) log-density (Z) from 1994 to 2010.</p

Empirical Orthogonal Function analysis.

<p>Projections on the first Empirical Orthogonal Function performed on kriged maps of log-density of each species (or group of species) from 1994 to 2010. The percentage of variance explained by this first axis is a proxy of the stability of the spatial distributions (see text). In parentheses are given, for comparison purposes, the percentages obtained from EOF applied on raw data.</p

Annual maps of hake.

<p>Kriged annual maps of European hake (<i>Merluccius merluccius</i>) log-density (Z) from 1994 to 2010.</p

Presence areas.

<p>Linear regressions between the presence area (given as a percentage of the whole study area) and log-abundance, for each key species.</p

Log-abundance in optimal habitats.

<p>Linear regressions between the log-abundance inside the optimal habitat and log-abundance over the whole area, for each key species. OH is a percentage that reflects the surface covered by the optimal habitat divided the surface of the whole study area (26 716 km²).</p

Average and variability maps and area classification for anchovies, sardines and sprats.

<p>Average and variability maps and area classification for anchovies, sardines and sprats.</p