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

Strandings represent a valuable source of information for the study of protected species such as cetaceans. In the Patagonian coast, five massive strandings of pilot whales, Globicephala melas edwardii, have been recorded in the last 30 years of study. These dolphins inhabit deep temperate and cool waters of all the southern hemisphere oceans, and although some aspects of their ecology are known, the available information about this species is very scarce. Therefore, given that the analysis of stomach contents allows studying the diet, among other ecological aspects, the aim of this work was to describe the main aspects of the feeding habits of this species, which is so difficult to access, based on the analysis of stomach contents of individuals stranded in Caleta Malaspina in 2009. To achieve this objective, the main prey consumed were identified, their size range was determined, and the main importance indices were calculated. The stomach contents of 22 females and 6 males were collected using a column of sieves of different mesh sizes. The taxonomic determination of the prey was based on the hard remains collected (fish bones and otoliths, cephalopod beaks, polychaete jaws, and crustacean exoskeletons). From the measurement of these structures, the length and wet weight of the prey were estimated by regressions, and then the numerical dominance (N%), frequency of occurrence (FO%), wet weight (PH%), and percent relative importance (IRI%) indices were calculated to identify the main prey items. On the other hand, specific overlap (SO) and general overlap (GO) analyses, as well as analyses of consumed sizes, were carried out to evaluate differences in resource use by females and males. It was found that all stomachs had contents and that the main prey were Illex argentinus (IRI% = 59.58%; N% = 35.05%; PH% = 76.45%) and Dorytheutis gahi (IRI% = 39.56%; N% = 61.06%; PH% = 12.97%), both with FO% = 100%. Other prey such as Enteroctopus megalocyathus, Patagonotothen ramsayi, Semirossia tenera, Callorhynchus callorhinchus, Eledone massyae, Iluocoetes fimbriatus, and Merluccius hubbsi were present with IRI% lower than 1%. I. argentinus had a mean dorsal mantle length and wet weight of 16.13±4.69 cm and 106.65±114.03 g, respectively, while for D. gahi, they were 8.46±1.76 cm and 10.37±8.47 g, respectively. Although no complete overlap was found between any of the subgroups considered, both indices (SO and GO) indicated a very similar use of resources. On the other hand, although statistically significant differences in the sizes of some prey were found between some subgroups, these do not have biological significance. Therefore, all dolphins in this stranding fed similarly, in terms of species and prey size.