Long-term and intrannual temporal changes in the distribution, biological and trophic conditions of continental slope fish below 1200 m in the NW Mediterranean

Abstract

Based on extensive trawling cruises using the same gear (OTSB-14 bottom trawl) and on the same sites (no less than 20 hauls between 1000-2300 m, in June-July) we identified long-term changes (comparing two periods: 1987-1989 vs 2010-2012) in the distribution and trophic condition of fish assemblages dwelling in the Balearic Basin (western Mediterranean). Fish with their Centre of Gravity (average depth distribution, CoG) exceeding 1400 m (e.g. Bathypterois mediterraneus, the rattails Coryphaenoides mediterraneus and C. guentheri) were distributed shallower in the 2010s. Based on stable isotopes analyses we also found a generalized decrease of the · 15N (trophic level) of fish (8 species, comparable sizes) between 0.23‰ to 3.25‰ from the 1980s to the 2010s. Gut fullness (F) and environmental variables related with water masses and food availability (Chl a, T, S) will be analyzed as explanatory variables of such changes. In addition the F and the biological indicators weight of gonads (GSI) and liver (HSI) were analyzed in 2008-2012 in a composite year on a seasonal basis for top 5 dominant species with CoG exceeding 1200 m (the 3 above cited and also Alepocephalus rostratus and L. lepidion). Preliminary analyses of GSI suggest seasonal peaks for some fish (B. mediterraneus in winter) and depth-related trends (A. rostratus), which coupling with prey availability will be tested. In general we found a different timing of reproduction and low spatial and temporal overlap in reproduction and food consumption