The role of environment on body condition of deep-sea fishes in the western Mediterranean

Abstract

Despite the long Mediterranean tradition in fishery investigations, studies on the influence of the environment on the population dynamics of exploited species are scarce, especially for deep-sea fishes. The aim of this contribution is to assess the link between body condition of nekto-benthic fishes and environmental features in two areas of the western Mediterranean, located in the Balearic (BsB) and the Algerian (AsB) sub-basins, with different geo-morphological and hydrodynamic characteristics. Two multidisciplinary surveys were carried out in December 2009 and July 2010: (i) one on board a commercial fishing boat to sample nekto- and epi-benthic communities; (ii) and (ii) another on board an oceanographic research vessel to collect hydrographic data and to sample zooplankton along the water column, as well as the meso-pelagic species of the deep scattering layers, which were detected by acoustic methods. Depths in the survey ranged from 200 and to 1000 m. Differences in community structure, fish condition of 15 exploited deep-sea fish species and environmental parameters were compared between areas and seasons, by means of uni- and multi-variant analysis and Generalized Linear Models. To estimate fish condition Fulton¿s (K) and relative condition (Kn) indices, as well as standardized residuals from the weight- length relationship, were used. Results showed a better fish condition in the BsB during in summer, despite differences among the three indices used. The oceanographic variables oxygen and fluorescence were significantly higher in the BsB during in summer season. , and sSimilar results were also obtained with respect to zooplankton, mesopelagic and epi-benthic communities, as potential preys for the nekto-benthic fish assemblages. These results show the importance of the environment on the condition of deep-sea fishes and suggest an important trophic coupling between the benthic and the pelagic domain in the Balearic Islands, one of the most oligotrophic areas of the western Mediterranean