Long-term changes in the composition of deep-sea fish assemblages in the Balearic Basin: influence of natural variability and human impact

Abstract

We analyzed long-term changes in slope assemblages (ca. at between 300 and 600 m) of the Balearic Basin and neighbouring areas around Balearic Islands (western Mediterranean) after compiling ca. 60 hauls (from commercial trawls) since 1950s-1960s to 2007. A preliminar analysis showed as the most clear tendency the rarefaction of some bathyal sharks since 1950s-1970s, among which the most clear example was Etmopterus spinax, an ovoviviparous shark probably highly vulnerable to changes experimented by deep-sea ecosystems. Possible changes in ecosystems induced by human impacts will be more in-deep analyzed, including the influence of traditional aspects (fishing effort, pollutans in fish tissues), but also broad-scale changes occurring in the deep Mediterranean related with Nile damming and long-term oceanographic changes in the intermediate and deep waters. Some of these changes are found coupled with the decline of the deep–sea shrimp Aristaeomorpha foliacea in the last 60s in the north-western Mediterranean