Isotopic evidence of structuring killer whale groups along the Southwestern South Atlantic Ocean

GARCÍA NÉSTOR ANÍBAL; VALES DAMIÁN GUILLERMO; LOIZAGA DE CASTRO, ROCÍO; CRESPO ENRIQUE ALBERTO

Viña del Mar

Conferencia; 11th ISOECOL, International Conference on Applications of Stable Isotope Techniques to Ecological Studies; 2018

Universidad Andres Bello

Killer whales (Orcinus orca) are large marine top predators that inhabit all oceans and are highlymobile. Despite being the most conspicuous top predator in the Southwestern Atlantic Ocean(SWAO), little is known about their ecology in the region. Here, we used carbon (δ13C) and nitrogen(δ15N) isotope analysis of bone collagen (n= 10) and dentine tooth (n= 3) from killer whales strandedbetween 28°S to 45°S during the period 1970-2014 to assess the trophic ecology of this species overthe Patagonian shelf. Muscle and skin of potential prey from the region were also isotopicallyanalyzed. Isotopic values of paired bone and tooth samples from 4 individuals were not significantlydifferent, hence samples were pooled. After correcting δ13C values to account for the Suess effect,Discriminant Analysis of Principal Components identified three distinct groups. Group 1 (Patagoniangroup, n= 8) included animals with high δ13C and δ15N values that after correcting for trophicdiscrimination factor (δ13C= 4.5, δ15N= 5) fitted with isotopic ratios of their potential prey over thePatagonian shelf, mainly pinnipeds, cetaceans, sharks and large bony fishes. In contrast, the tworemaining groups had δ13C and δ15N values that do not correspond with the potential prey from thePatagonian shelf, suggesting that they were foraging mainly in adjacent ecosystems. Group 2(Subtropical group, n= 3) is characterized by individuals with low δ15N and high δ13C values thatcorresponded with the isotopic values reported for killer whales stranded in southern Brazil. Group3 (Subantarctic/Antarctic group, n= 2) were individuals with low δ13C and δ15N values, which aretypical from high latitude waters. The presence of killer whales trophic groups over the Patagonianshelf suggests the existence of structuring subpopulations exploiting specific habitats. Moreover, oneof the individuals from the Patagonian group shares haplotype with conspecific fromSubantactic/Antarctic waters, revealing some degree of connectivity between populations amongthese large marine ecosystems. Nonetheless, population genetic studies are needed to confirm thepopulation structure and migration along SWAO. Our results further the scarce ecological knowledgefor the species in the region, while presents the basis to infer more complex ecological hypothesis