Stomach contents of long-finned pilot whales (Globicephala melas edwardii) mass-stranded on the Argentine Patagonian coast in 2009

CHALCOBSKY, AILEN; GARCÍA, NÉSTOR A.; COSCARELLA, MARIANO A.; CRESPO, ENRIQUE A.

MARINE MAMMAL SCIENCE

WILEY-BLACKWELL PUBLISHING, INC

Año: 2022 vol. 38 p. 1229 - 1241

0824-0469

Fifty long-finned pilot whales, G. melas edwardii, (19 males and 31 females) stranded at Caleta Malaspina, close to Bahía Bustamante, Chubut, Argentina (Figure 1). The site of stranding is a long creek system (11 km) with a soft bottom, gentle slope, and numerous islands and islets that remain underwater during high tide (14 m depth) and uncovered with low tide (7 m depth). The stranding occurred a few days before it was discovered on September 12, 2009, in an area protected under the administration of the Subsecretaría de Turismo y _ Areas Protegidas. Stomachs and intestines were removed from 28 individuals (6 males and 22 females). It was not possible to sample the remaining individuals due to difficulties in accessing the carcasses. The stomachs collected were frozen at -20°C until processed.The most important prey species were I. argentinus (IRI% = 59.58) and D. gahi (IRI% = 39.56), which together add up to an IRI% = 99.14 (Table 1). Both I. argentinus and D. gahi were present in all stomachs (FO% = 100) but while I. argentinus comprised the highest proportion of the diet by wet weight (W%), D. gahi comprised the highestproportion by number (N%). The third species in order of importance was M. ingens (IRI% = 0.34) and the fourth one was E. megalocyathus (IRI% = 0.24). The rest of prey taxa represented IRI% ≤ 0.1. When grouped according to their habitat preference (i.e., habitat group, see Table 2), the most important group, with IRI% = 98.14, was the demersalpelagic, with I. argentinus, D. gahi, and M. hubbsi included.The presence of several prey species that have not been recorded previously as part of long-finned pilot whale diet is remarkable; there were C. callorhynchus, I. fimbriatus, P. ramsayi, E. massyae, and S. tenera. These species presented an IRI% < 0.1 but are common in the Southwest Atlantic (Cousseau, 1997; Cousseau & Perrotta, 1998). Particularly important is the presence of C. callorhynchus because it is the first record of a cartilaginous fish in the stomach contents of long-finned pilot whales in the Southern Hemisphere. In the Northern Hemisphere, the cartilaginous fish, Squalus acanthias, was reported (average size of 75 cm and 1.640 g, similar size to C. callorhynchus in this study) fromstomach contents of long-finned pilot whales stranded along the US Atlantic coast (Gannon et al., 1997). The usual absence of cartilaginous fish in diet analysis of pilot whales could be related to the preference for other types of prey or, perhaps these cartilaginous fish are being underestimated in stomach content analysis because they are digested faster than bony fish (Pierce & Boyle, 1991). Both C. callorhynchus and S. acanthias have very prominent dorsal spines, with chitinous composition, that allow specific identification (Compagno, 1984). Given the distribution of the prey species identified in this study (Haimovici et al., 1998; Hatfield et al., 1990),we can conclude that this pod of pilot whales fed on demersal-pelagic prey in the Argentine continental shelf, which is striking given the preferred oceanic distribution of these predators, highlighting that the feeding habits of the long-finned pilot whales varies with the geographic features of their habitat.