## 1 Introduction  
The marine world is rapidly changing as humans perform a number of activities, such as fish stocking, shipping, aquaculture, pollution and habitat modification, which result in ecological and economic damage. Species distribution models (SDMs) provide a measure of species occupancy in response to the local/regional oceanographic and environmental conditions and habitat [1]. Such models combine occurrence locations of known species with a series of environmental layers, by developing a statistical inference system which unveils the impact of environmental parameters on specific species distribution patterns and by expanding the species distribution layer towards unknown areas. Distribution models for marine organisms and habitat mapping are essential tools in understanding the links between the ecology of marine fishes and the factors that affect species presence/absence patterns [2]. The ecosystem approach to fisheries has been gaining attention, with spatial fishing restrictions and marine protected areas being considered as vital tools against overfishing [3]. Reliable distribution models with high resolution and extensive coverage are required to improve and replace existing ones (i.e., AquaMaps www.aquamaps.org from FishBase www.fishbase.de). Furthermore, the improvement of fish distribution models is of great importance within the context of climate change [4], especially in the case of the Mediterranean Sea, where the number of marine species migrating through the Suez Canal--as a result of sea warming (among other factors)--has been increasing rapidly during the last 20 years [5]. Sea warming also affects the native marine fauna of the Mediterranean Sea, by changing their geographical distribution, depending on thermal preferences of each species [6]. Species with preference for warmer waters expand northwards and increase their abundance, whereas species with preference for colder waters decline in abundance and restrict their range [7]. Small and medium pelagic fishes are highly affected by oceanographic, environmental, and climatic changes, as well as by human impact. They correspond to about one quarter of the globally exploited marine fisheries catch, while clupeoid species account to more than 40% of the total catches in the Mediterranean Sea [8]. European sardine (_Sardina pilchardus_) and European anchovy (_Engraulis encrasicolus_) make up the vast majority of landings across the western, central, and eastern Mediterranean [9]. In the Mediterranean Sea, small pelagic fishes are mainly being exploited by the purse-seine fleet, which also collects, albeit at lower quantities, medium pelagic fishes such as Atlantic mackerel (_Somber scombrus_), Atlantic chub mackerel (_Somber colias_), and horse mackerels (_Trachurus_ spp.). Limited quantities of small and medium pelagic fishes are also caught by bottom-trawlers and boat-seiners depending on the area and the season. The landings of most small pelagic species in most areas of the Mediterranean Sea appear to be declining partly due to their overexploitation and partly due to climate and environmental forcing. Because of their fast life history strategy (rapid growth, early maturity, short lifespan), small pelagic fishes and especially their recruitment [10] are dependent on climate and environmental factors [9; 11; 12; 13]. Although the environmental effects on fish species distribution and population dynamics in terms of presence/absence or probability of occurrence have been described well enough at various parts of the Mediterranean [14; 15; 16], a comprehensive approach to the relative impact of each environmental component on fish species distribution for the whole Sea is still missing. SDMs, or else 'environmental niche models', may provide quantified relationships between fish species occurrence and environmental predictors, while assuming other ecological processes as unimportant.