Extralimital occurrence of the hourglass dolphin (Cephalorhynchus cruciger) in northern Patagonia

Abstract

The hourglass dolphin (Cephalorhynchus cruciger) is a poorly known oceanic marine mammal species with a circumpolardistribution in Antarctic and sub-Antarctic waters, with records outside its typical range being exceedingly rare. Here,we report the first documented record of this species in northern Argentine Patagonia (40°48′S, 65°05′W, southwesternSouth Atlantic), based on the sighting, stranding, and subsequent necropsy of a single individual in the San Matías Gulf,Argentina. The animal exhibited prolonged nearshore presence, repeated live strandings, and markedly poor body condition(BCS = 1). Stomach contents consisted exclusively of macroalgae (Dictyota dichotoma) and plastic debris, with noidentifiable prey remains. The combination of extralimital occurrence, abnormal behavior, emaciated condition, and atypicalstomach contents suggests that this individual represents a debilitated vagrant rather than evidence of a distributionalshift. Plastic ingestion was considered incidental and unlikely to have been a primary cause of death. This case highlightsthe value of stranding events as opportunities to obtain biological and ecological information for poorly known oceanicspecies, and contributes to the limited knowledge of C. cruciger in the southwestern South Atlantic.