Unusual occurrence of a mixed pod of false killer whales (Pseudorca crassidens) and common bottlenose dolphins (Tursiops truncatus) in the Beagle Channel (Argentina)

Abstract

Nonaggressive mixed species groups of false killer whales (Pseudorca crassidens) and common bottlenose dolphins (Tursiops truncatus) are frequently observed at many locations around the world, but they are not commonly seen in Tierra del Fuego. This work reports the first sighting of a mixed pod of false killer whales and common bottlenose dolphins and its live mass-stranding event in the inner Beagle Channel, Tierra del Fuego (Argentina) in February 2022. The mixed pod was confirmed to be composed of ~ 50 false killer whales (including calves) and four common bottlenose dolphins, but only false killer whales were involved in the mass-stranding event which occurred at the inner and western sector of Ushuaia Bay next to urban settings. The interaction of natural and human-related factors appears to have caused the mass-stranding in this case; however, the reasons why the pod was inside the channel are still unknown. Although all animals were rescued alive, two animals were found dead days after the event. These sightings and stranding may be considered extralimital records for Tursiops truncatus and add new records in their southernmost (summer) range for Pseudorca crassidens. The handling of the situation during these events also suggest that a better marine mammal-stranding network response program is needed in this southern region.