Risso's dolphin Grampus griseus in the Mediterranean Sea

Abstract

The ecology and status of Risso's dolphins Grampus griseus worldwide are poorly known. In the Mediterranean Sea, modern field studies of cetaceans only began in the late 1980s and this has resulted in rapid advances in knowledge of some species, but not Risso's dolphin. This paper reviews available information on the distribution and ecology of Risso's dolphins in the Mediterranean and identifies factors that may negatively affect them in this region. Risso's dolphins occur in continental slope waters throughout the Mediterranean basin and around many of the region's offshore islands and archipelagos. No synoptic estimate of abundance is available for the Mediterranean region, but densities and overall numbers are low in comparison to some other small odontocetes. Diet consists primarily of cephalopods, with a clear preference for mesopelagic squid. The principal known threat to populations in the Mediterranean is entanglement in pelagic drift gillnets. Other potential problems for Risso's dolphins in the Mediterranean include noise disturbance and ingestion of plastic debris. Conservation actions to mitigate the risk of entanglement in fishing gear are likely to benefit Risso's dolphins; specifically, the existing driftnet ban in EU waters should be strictly enforced and extended to the high seas and to waters under non-EU State jurisdiction. More and better data are needed on abundance, distribution, movements, population dynamics and trends in Risso's dolphin populations, and better information on threats (e.g. bycatch in fishing gear) is needed to inform conservation efforts.