## 2 Materials and Methods
### Species Data  
In this study, eight commercial fish species were chosen for analysis and prediction. This selection was based on the following criteria: (i) these species represent the most common commercial fish in the Mediterranean Sea, occurring in a plethora of locations, (ii) they are pelagic species living in different depth ranges, and (iii) they demonstrate a variety of preferred environmental conditions, especially at the upper parts of the water column. It is a challenging task to create a single generic model that performs the best for all species. Most of these pelagic fish species are small and medium-sized, and the depth range of each appears in Table 1: European anchovy (_Engraulis encrasicolus_), European pilchard or Sardine (_Sardina pilchardus_), round Sardinella (_Sardinella aurita_), Atlantic chub mackerel (_Scomber colias_), Atlantic mackerel (_Scomber scombrus_), picarel (_Spicara smaris_), Atlantic bluefin tuna (_Thumus thynmus_) and Swordfish (_Xiphias gladius_). Anchovy is a summer spawning (April to September in the Mediterranean), fast growing, short living, and early maturing small pelagic fish [40; 41]. It is a low trophic level planktivorous species with preference for warm water temperatures [9]. Together with sardine, they constitute around 40% of the total marine fishery landings in the Mediterranean, a percentage that fluctuates depending on the country and which is highest along the northern Mediterranean coastline [9]. Sardine is a winter spawning (October to March in the Mediterranean), fast growing, and early maturing small pelagic fish with a short lifespan [41] that primarily feeds on zooplankton and is preyed upon by large pelagic fish, marine mammals, and seabirds. It generally prefers low water temperatures and constitutes around 20% of the marine fishery landings in the Mediterranean Sea, especially along the northern coastline [9]. Sardine and anchovy alternate in high abundances and landings [42]. Round sardinella is also a fast growing and early maturing small pelagic fish with short lifespan, which spawns over a narrower (May to July in the Mediterranean Sea) time period [43]. It feeds mainly on zooplankton [44] and has a strong preference for warm waters [9]. Although its abundance is increasing across the Mediterranean Sea as a result of sea warming (western Mediterranean: [45]; eastern Mediterranean: [46]), round sardinella's contribution to marine fishery landings is confined to the southern Mediterranean coastline. Atlantic chub mackerel is a medium sized pelagic fish, which spawns over late-spring/early -summer months (May to June) in the Mediterranean Sea [47]. Its growth rate is medium and its lifespan is around 7 years [48]. It is a high trophic level species as it feeds on fish and zooplankton [48] and prefers warm waters [9]. Atlantic chub mackerel is a commercial species in many Mediterranean countries. Atlantic mackerel is a medium sized pelagic fish, which spawns during winter (December to March) in the Mediterranean Sea [47]. It grows at a medium rate and may reach 17 years of age [48]. It is positioned high in the food web and prefers cold waters [9]. Similar to chub mackerel, Atlantic mackerel is a commercial species in most Mediterranean countries. \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Scientific Name** & **Common Name** & **Depth** & **Samples** \\ \hline _E. encrasicolus_ & European anchovy & 0–400 & 729 \\ _S. pilchardus_ & European pilchard & 10–100 & 596 \\ _S. aurita_ & Round sardinella & 0–80 & 720 \\ _S. colias_ & Atlantic chub mackerel & 0–300 & 676 \\ _S. scombrus_ & Atlantic mackerel & 0–1000 & 807 \\ _S. smais_ & Picarel & 15–328 & 1225 \\ _T. thynmus_ & Bluefin tuna & 0–1000 & 1237 \\ _X. gladius_ & Swordfish & 0–3000 & 1230 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Species of the present study and number of observations. Picarel is a small-sized hermaphroditic spring spawning species (April to May), which spawns on sandy bottoms where nests are excavated [49].