Habitat Suitability Modeling to Identify the Potential Nursery Grounds of the Atlantic Mackerel and Its Relation to Oceanographic Conditions in the Mediterranean Sea

Our knowledge for the distribution of Atlantic mackerel (Scomber scombrus) in the Mediterranean Sea is limited and fragmented. In the current work habitat suitability modeling was applied to summer acoustic surveys data of Atlantic mackerel juveniles derived from the north part of the Mediterranean (i.e., acoustic data from the Gulf of Lions, pelagic trawls held during acoustic surveys in Spanish Mediterranean waters, south Adriatic Sea, Strait of Sicily, and North Aegean Sea) using generalized additive models (GAMs) along with satellite environmental and bathymetry data. Bathymetry along with sea surface temperature and circulation patterns, expressed through sea level anomaly and the zonal component of the absolute geostrophic velocity, were the environmental variables best to describe nursery grounds. The selected model was used to produce maps presenting the potential nursery grounds of Atlantic mackerel throughout the Mediterranean Sea as a measure of habitat adequacy. However, the assessed potential nursery grounds were generally marked as “occasional,” implying that although there are areas presenting high probability to encounter Atlantic mackerel, this picture can largely vary from year to year stressing the high susceptibility of the species to environmental conditions. In a further step and toward a spatial management perspective, we have estimated and visualized the overlap between Atlantic mackerel and anchovy/ sardine juvenile grounds throughout the basin. Results showed that although the degree of overlapping was generally low, not exceeding 15% in general, this varied at a regional level going up to 30%. The potential of the output of this work for management purposes like the implementation of spatially-explicit management tools is discussedVersión del edito

Density dependence in the spatial behaviour of anchovy and sardine across Mediterranean systems

A spatial indicator—the spreading area index—is used to describe anchovy and sardine spatial distribution in relation to biomass variation and to look for ecosystem differences within the Mediterranean basin. Specifically, the variation in the spreading area index in relation to biomass was examined for different areas of the Mediterranean Sea (i.e. Aegean Sea, western Adriatic Sea, Strait of Sicily, Gulf of Lion, and Spanish Mediterranean waters). In order to capture the spatial variability of the population at different levels of fish density, acoustic survey data for the years of highest, lowest, and intermediate abundance were used. In a subsequent step standardized values of spreading area and biomass were estimated to allow comparisons. Results showed pronounced area differences. A significant relationship was revealed in the case of anchovy for areas with extended continental shelf (i.e. Aegean Sea, Adriatic Sea, and Gulf of Lion), indicating an increase in biomass with an increase in the spreading area. No relationship was found for areas dominated by narrow continental shelf and strong currents (i.e. Spanish Mediterranean waters and the Strait of Sicily). With regard to sardine, an increase in biomass was followed by an increase in the spreading area when estimates from the Aegean Sea, the Adriatic Sea, and the Strait of Sicily were considered together. The relationship was even more Abstracts–Theme Session B 9 pronounced when analysis was limited to the Aegean Sea and the Strait of Sicily. No relationship was found for the Spanish Mediterranean waters and the Gulf of Lion. This clearly implies that spatial indicators should be integrated into ecosystem management, taking into account that they can be area‐ or ecosystem‐dependent

Habitat suitability modelling for sardine Sardina pilchardus in a highly diverse ecosystem: the Mediterranean Sea

Integrated information from different parts of the Mediterranean Sea was used to model the spatial and temporal variability of the distribution grounds of the sardine population. Acoustic data from the North Aegean Sea (Eastern Mediterranean), the Adriatic Sea (Central Mediterranean), the Sicily Channel (Central Mediterranean) and Spanish Mediterranean waters (Western Mediterranean) were analysed along with satellite environmental and bathymetric data to model the potential habitat of sardine during summer, autumn and early winter. Generalized additive models were applied in a presence−absence approach. Models were validated in terms of their predictive ability and used to construct maps exhibiting the probability of sardine presence throughout the entire Mediterranean basin as a measure of habitat adequacy for sardine. Bottom depth and sea surface temperature were the environmental variables that explained most of the data variability. Several areas along the Mediterranean coastline were indicated as suitable habitat for sardine in different seasons. An expansion of these areas over the continental shelf, up to 100 m depth, was consistently noticed from summer to winter. This was attributed to the horizontal movements of sardine related to spawning (i.e. winter period) and the peculiarities of the Mediterranean Sea where areas favouring growth, feeding and spawning processes tend to be localised and prevent a long range, offshore migration as opposed to large upwelling ecosystems. Moreover, within the study period, a positive relationship between the extent of sardine preferred habitat and landings was revealed for both summer and winter seasons throughout the entire Mediterranean SeaPublicado