Clues from the recent past to assess recruitment of Mediterranean small pelagic fishes under sea warming scenarios

Knowledge of the effect of environmental variables on the early life history of fishes is essential to assess the effect of future environmental changes on the recruitment of commercial species. We investigate the effect of sea warming on two small pelagic fishes (Engraulis encrasicolus and Sardinella aurita) in the NW Mediterranean Sea based on the analysis of ichthyoplankton data collected in two surveys of contrasting conditions: the exceptionally warm summer of 2003, which may be indicative of conditions under future climate change scenarios, and the summer of 2004, with temperatures within the climatic average for the period 2000-2012. We use fine-resolution environmental variables measured locally and Generalized Additive Models to assess the influence of environment on these two summer-spawning small pelagic fishes. We show that sea surface temperature is the main environmental factor explaining abundance, but other factors (food availability and water currents) have additional roles tuning the effect of temperature. In the hot summer of 2003 we observed a decline of local egg production of anchovy and an increase of larval advection from the colder Gulf of Lions compared to 2004. Round sardinella spawning was higher in 2003 than in 2004 and extended over a wider area, but larvae viability was compromised by the lower availability of trophic resources. We hypothesize that future changes in environmental forcing on these two co-occurring summer spawning species will determine differential larval survival, with cascading effects on the upper trophic levels which feed on these species, including negative impacts on their fisheries.