Abstract
Predicting the occurrence of keystone top predators in a multispecies marine environment, such as the Mediterranean Sea, can be of considerable value to the long-term sustainable development of the fishing industry and to the protection of biodiversity. We analysed fisheries independent scientific bottom trawl survey data of two of the most abundant cartilaginous fish species (Scyliorhinus canicula, Raja clavata) in the Aegean Sea covering an 11-year sampling period. The current findings revealed a declining trend in R. clavata and S. canicula abundance from the late ′90 s until 2004. Habitats with the higher probability of finding cartilaginous fish present were those located in intermediate waters (depth: 200–400 m). The present results also indicated a preferential species' clustering in specific geographic and bathymetric regions of the Aegean Sea. Depth appeared to be one of the key determining factors for the selection of habitats for all species examined. With cartilaginous fish species being among the more biologically sensitive fish species taken in European marine fisheries, our findings, which are based on a standardized scientific survey, can contribute to the rational exploitation and management of their stocks by providing important information on temporal abundance trends and habitat preferences.
Highlights
Cartilaginous fish constitute an ancient conservative taxonomic group that was very abundant in the world oceans
The species most frequently caught with this gear, depending on depth and areas [9,10,11,12] are: Galeus melastomus, Scyliorhinus canicula, Etmopterus spinax, Raja clavata, Raja asterias and Squalus acanthias
We modeled the abundance data as functions of spatial and temporal variables, in order to identify spatio-temporal trends and built abundance density maps demonstrating on a quantitative basis the distribution of four of the most abundant cartilaginous fish species in the Aegean Sea: Scyliorhinus canicula (Linnaeus, 1758) and Raja clavata (Linnaeus, 1758), representing more than 74% of the total demersal elasmobranch abundance caught during the period 1998–2008. (Table 1)
Summary
Cartilaginous fish constitute an ancient conservative taxonomic group that was very abundant in the world oceans Their abundance has progressively declined over time worldwide and many species are considered vulnerable or endangered [1,2,3,4,5]. We modeled the abundance data as functions of spatial and temporal variables, in order to identify spatio-temporal trends and built abundance density maps demonstrating on a quantitative basis the distribution of four of the most abundant cartilaginous fish species in the Aegean Sea: Scyliorhinus canicula (Linnaeus, 1758) (smallspotted catshark) and Raja clavata (Linnaeus, 1758) (thornback ray), representing more than 74% of the total demersal elasmobranch abundance caught during the period 1998–2008. The overall abundance of cartilaginous species is modeled
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