Diet of Risso's dolphin (<i>Grampus griseus</i>) in the western Mediterranean Sea

Abstract

SUMMARY: The diet of Risso's dolphin in the Mediterranean is described based on 15 animals stranded between 40º25'N 00º32'W and 37º35'N 00º45'E from April 1987 to January 2003. The prey were mainly oceanic cephalopods. Pelagic octopods, especially A. argo, were the most abundant (mean = 41.28%; SD±34.32). Species belonging to the families Ommastrephidae, Histioteuthidae and Onychoteuthidae were also frequent components of its diet. The bathymetric distribution of cephalopods shows that Risso's dolphin preferentially feeds on the middle slope (600 to 800 m depth) in the Mediterranean.Keywords: Grampus griseus, cetacean, cephalopods, diet, slope, Mediterranean.RESUMEN: DIETA DEL DELFÍN DE RISSO (GRAMPUS GRISEUS) EN EL MEDITERRÁNEO OCCIDENTAL. -Se ha analizado el contenido gastrointestinal de quince ejemplares de Grampus griseus varados en el Mediterráneo occidental entre 40º25'N 00º32'W y 37º35'N 00º45'E durante el período1987 a 2003. Los resultados indican una dieta teutófaga, basada principalmente en cefalópodos oceánicos destacando los octópodos pelágicos, especialmente Argonauta argo, como la presa más abundante (media = 41,28%; SD±34,32). Algunas especies pertenecientes a las familias Ommastrephidae, Histioteuthidae y Onychoteuthidae son también componentes frecuentes de la misma. La distribución batimétrica de los cefalópodos indica que el área de alimentación de este delfín se localiza preferentemente sobre el talud continental medio (600-800 m de profundidad).

Toothed whales in the northwestern Mediterranean: Insight into their feeding ecology using chemical tracers

“…The stomach contents of pilot whales were composed of 10-20% Histioteuthidae (Astruc, 2005). The stomach contents of Risso's dolphins were very variable, containing between 15% and 80% Histioteuthidae (Astruc, 2005;Blanco et al, 2006;Clarke, 1996;Würtz et al, 1992). However, individuals stranded in France and Italy presented a higher percentage of Histioteuthidae, from 40% to 80% (Astruc, 2005;Würtz et al, 1992).…”

“…In Spain, the stomach contents were mainly composed of Argonauta argo (40%), while in Italy, the stomach contents of Risso's dolphins were mainly composed of Histioteuthis reversa (80%). The remaining stomach contents were composed of several other squids and octopods (Blanco et al, 2006;Würtz et al, 1992). Therefore, these toothed whale species are strictly cephalopod feeders and may compete for a certain part of their diet.…”

“…Unpublished data for the pilot whale seems to show a diet with around 50% Todarodes sagittatus, 10-20% Histioteuthidae and around 30% other squid and octopus species (Astruc, 2005). Stomach content analysis in Risso's dolphin was performed in 14 specimens stranded on Spanish coasts (Blanco et al, 2006) and in one specimen in Italy (Würtz et al, 1992). In Spain, the stomach contents were mainly composed of Argonauta argo (40%), while in Italy, the stomach contents of Risso's dolphins were mainly composed of Histioteuthis reversa (80%).…”

Uncommon pelagic and deep-sea cephalopods in the Mediterranean: new data and literature review

“…In most cases, the reports refer to the sporadic findings of single individuals, such as the one reported by Mangold-Wirz (1973), in the north western basin or the specimen taken by Maiorano et al (2010), at 558 m depth, in a trawl survey series undertaken between 1985 and 2006 in the Ionian Sea. The species, however, could be abundant, as it is the predominant prey of different predators captured in this area, including the giant red shrimp and two species of dolphins (Bello & Pipitone, 2002;Blanco et al, 1995Blanco et al, , 2006. Of note is the species was not found to be the prey of teuthophagous predators from outside the Mediterranean, in the literature reviewed.…”

Consumption of pelagic tunicates by cetaceans calves in the Mediterranean Sea

“…Interestingly, there have also been a few reports about gelatinous zooplankton in the stomach contents of apex, endothermic predators, such as cetaceans (e.g. Blanco et al, 2006), but the ecological meaning of these observations is open to interpretation. It is possible that gelatinous zooplankton is accidentally consumed by cetaceans or represents secondary prey (i.e.…”