A study published in Royal Society Open Science revealed that mass strandings of common dolphins in Argentine Patagonia are related to the presence of orcas as predators.
The research focused on San Antonio Bay, in the San Matías Gulf, where the cetaceans entered shallow waters in response to stress, becoming trapped in sandbanks.
Recent Events
Between 2021 and 2023, two significant episodes were recorded:
- September 2021: 52 common dolphins died; necropsies were performed on 38 specimens.
- April 2023: around 570 dolphins were stranded, although all were returned to the sea thanks to the intervention of volunteers and authorities.
The analyses ruled out human causes, diseases, or malnutrition. The animals were in good physical condition, reinforcing the hypothesis that the trigger was predator avoidance.
Predator-Prey Dynamics
The team led by Magdalena Arias concluded that the presence of orcas generates extreme stress in the dolphins, which group into compact formations and swim towards shallow areas to escape. This gregarious behavior amplifies the effect of panic: when part of the group flees towards the coast, the rest imitate, increasing the risk of stranding.
The geography of the bay, with sandbanks and intense tides, further elevates the probability of the animals becoming trapped.
Community Response
During the 2023 event, volunteers used kayaks and small boats to guide the dolphins back to the sea. Coordination among scientists, fishermen, and the local community was key to preventing deaths.
The study highlights that identifying the natural cause of these events allows for optimized rescue responses and reduces unjustified alarms about diseases or pollution.
Ecological Implications
The research challenges the previous view that mass strandings were solely linked to human or environmental factors. The predator-prey dynamics emerge as a decisive natural factor.
The increasing presence of orcas in the San Matías Gulf poses new pressures on dolphins and other marine species. Constant monitoring will be essential to anticipate risks and strengthen emergency management.
The study concludes that the pressure exerted by predators like orcas can significantly alter dolphin behavior and contribute to mass strandings. This finding redefines the understanding of these phenomena and underscores the need to integrate natural factors into marine conservation strategies in Patagonia.
