Influence of physical environmental factors on the composition and horizontal distribution of summer larval fish assemblages off Mallorca island (Balearic archipelago, western Mediterranean)

Abstract

Two ichthyoplankton surveys were carried out in two areas off Mallorca island (Balearic archipelago, western Mediterranean) in June 1996 and August 1996, respectively. The aim of both surveys was to assess the influence of physical environmental factors on the horizontal distribution of larval fish assemblages, focusing on larvae of large migratory pelagic fish species. Canonical correspondence analysis (CCA) indicated that in the June survey, the patterns of horizontal distribution of fish larvae were mainly conditioned by depth and by the distribution of two surface water masses: the Modified Atlantic Waters (MAW), of recent Atlantic origin, and the older Surface Mediterranean Waters (SMW). The effect of depth gradient was clear in mesopelagic and neritic species, but it was not so evident in the larvae of large pelagic species which presented a highly patchy distribution. Contrastingly, the August patterns of horizontal fish larvae distribution were significantly correlated with the surface salinity gradient resulting from successive MAW inflows, whereas depth did not show any significant effect, probably linked to the bottom topography with a very narrow shelf area. The data obtained highlight that the Balearic Islands constitute an important spawning ground for most of the large pelagic fishes inhabiting Mediterranean waters, both highly migratory and resident species