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... Risso's dolphins can be found from the tropics through the temperate regions in both hemispheres (Leatherwood et al., 1980;Jefferson et al., 1993;Kruse et al., 1999;Taylor et al., 2008). They are rarely found in waters cooler than 10 • C (Kruse et al., 1999;Baird, 2009). ...
... The Risso's dolphin has been assessed by IUCN as a species of Least Concern (Taylor et al., 2008). While there is not even a reasonable guess at the total numbers of Risso's dolphins worldwide, a few estimates exist for specific areas. ...
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.
Ecotoxicological and pathological research on Grampus griseus (Cuvier, 1812) (Risso's dolphins) is scarce both globally and in the Mediterranean Sea. This species has been classified as “Vulnerable” by the International Union for Conservation of Nature (IUCN) in the Mediterranean Sea. To evaluate the presence of “persistent organic pollutants” (POPs), especially organochlorine compounds (OCs), in the animals, chemical analyses were performed on tissues and organs of Risso's dolphin stranded along the Italian coasts between 1998 and 2021. Toxic contaminants such as hexachlorobenzene (HCB), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane and its metabolites (DDTs) were examined in the blubber, liver, muscle, and brain of 20 animals, and data was correlated with sex, age, and stranding locations.