Cephalopods in the diet of Risso's dolphin (Grampus griseus) from the Mediterranean Sea: A review

The Risso's dolphin, Grampus griseus, is a deep-sea cetacean with a predominantly teuthophagous diet. Its distribution in the northwest Mediterranean is generally in deeper waters, but there is little information on diet or feeding areas. To extend knowledge of the diet of G. griseus, the stomach contents of six stranded Risso's dolphins in the Mediterranean Sea were analyzed. A total of 578 cephalopod beaks (166 uppers and 392 lowers) were found, identified as 386 individuals from 19 different species of Coleoidea cephalopods, one Sepiolida, eight Octopoda, and ten species belonging to the Order Oegopsida. This adds six species of cephalopods to those previously recorded in the Mediterranean Sea: Rondeletiola minor, Eledone moschata, Scaeurgus unicirrhus, Bathypolypus sponsalis, Pteroctopus tetracirrhus and Taonius pavo. In this study the most abundant prey family was Histioteuthidae. In addition, based on the available literature, the diet of 39 Risso's dolphins was reviewed in Mediterranean waters. The abundance of cephalopod species in the diet of these specimens was compared according to genus, geographical area, season, and age. The habitat of the prey of G. griseus was reviewed, suggesting a teuthophagous diet in this area. This study helps to identify both the prey species and the areas where prey are available in the northwest Mediterranean, which are key factors in establishing the limits and regulations of the "Northwest Mediterranean Sea, Slope and Canyon IMMA System" (Important Areas for Marine Mammals) proposed by the Working Group on Marine Mammal Protected Areas (MMPATF - IUCN).