Dolphin Stranded in San Antonio Bay, Argentina
In a shocking event, hundreds of dolphins found themselves trapped in Argentina while trying to escape relentless killer whales, highlighting a troubling situation for marine wildlife.
Footage shared on social media and various citizen science platforms has played a crucial role in helping experts understand the underlying causes of two significant mass strandings that occurred in recent years. According to Magdalena Arias from the Argentine National Council for Scientific and Technological Research, “This does not mean that predators are always to blame for mass strandings; however, it indicates that predator-prey dynamics can trigger such events under certain conditions, particularly when influenced by coastal geography, water currents, and the dolphins’ cohesive social behavior.”
Marine mammals have been experiencing mass mortality for millennia, yet scientists continue to debate the reasons behind this phenomenon. Potential causes include human interference, toxic algal blooms, infectious diseases, disorientation, overpopulation, natural disasters, and misguided hunting practices.
Some researchers have speculated that the dolphins may have been stranded due to fleeing a predator. This phenomenon is complicated by the vast areas predators can cover and the prolonged nature of hunts, making documentation challenging. Often, scientists only observe the aftermath: a healthy pod of dolphins washed ashore.
Over the past five years, the species Mileka (Delphinus Delphis) has been involved in three separate stranding incidents in Northern Patagonia, an unprecedented trend. Consequently, Arias and her team initiated detailed investigations.
Researchers utilized video data collected from drones and mobile phones through citizen science platforms like e-whale, alongside contributions from tourists, local fishermen, and residents.
In 2021, approximately 350 dolphins, pursued by a pod of eight killer whales, raced toward San Antonio Bay in Argentina’s Rio Negro province. About 30 minutes later, the killer whales retraced their route into the ocean, but several dolphins, panicked, sought refuge in a shallow harbor. Tragically, the next day, numerous dolphins were found dead in that same harbor.
https://www.youtube.com/watch?v=2ng7FJGwOD0" title="Mass Stranding of Dolphins
Similarly, in 2023, around 570 dolphins sprinted into the bay, closely followed by a pod of killer whales. Although some dolphins managed to enter the harbor, local officials and volunteers successfully rescued them as the killer whales veered away.
Necropsies performed on 38 deceased dolphins from the 2021 incident indicated that the animals were in good health with no significant injuries. Notably, their stomach contents revealed no recent meals, suggesting they had not been actively pursuing prey. This finding raises doubts about the most common theories surrounding mass strandings, according to Arias.
By analyzing reports of killer whale sightings, the research team developed a timeline detailing orca activity in the area, revealing two confirmed instances of killer whales hunting and preying on dolphins.
It is likely the dolphins sought refuge in shallow waters, which hindered the orcas’ echolocation capabilities and prevented their movement. However, this strategy backfired, as the dolphins became trapped between sandbars and tidal channels, Arias explained.
Conversely, it is possible that killer whales purposely herd dolphins into the bay to trap them. Evidence suggests that two killer whales observed during the 2021 incident frequently exploited offshore formations to catch sea lions.
The extended stress and disorientation resulting from the chase may have dissuaded the dolphins from returning to deeper waters. Arias emphasized that situations like this likely occur worldwide, but remain largely undocumented.
“This study underscores the pivotal role of citizen science in advancing research efforts. Understanding these interactions not only sheds light on mass strandings but also enhances our knowledge of shifting marine ecosystems and species responses,” she concluded.
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Source: www.newscientist.com
