The appearance of 26 dead orcas, belonging to an extremely rare variety, on a beach in northern Tierra del Fuego, has caused great surprise in the scientific community.
The event is considered unusual, as there are no precedents in the region and very few similar cases worldwide have been recorded.
The process began with the discovery of two specimens of the “ecotype D,” a very rare variant of orca. It was the provincial park rangers who detected them in Bahía San Sebastián, within the Atlantic Coast Provincial Reserve, during a routine patrol.
This initial discovery triggered alerts from the Austral Center for Scientific Research (CADIC-Conicet) and the laboratory of Research on Southern Marine Mammals (IMMA). Following protocol, a team of specialists began the task of reconstructing what had happened to the animals.
To this first discovery was added another weeks later, and the surprise of the researchers multiplied: an additional two dozen specimens of the same variety of orcas were found stranded in a hard-to-reach area located north of the gulf.
The biologists from IMMA proceeded to record the position of the animals, determine the sex and age class of each individual. In addition, they took body measurements, took photographs, and collected skin samples to be analyzed in the laboratory.
In a first visual inspection, the specialists did not detect any signs of interaction with human activities. The orcas’ bodies lacked cuts, bruises, or traumas consistent with boat strikes, as well as marks from fishing nets or lines.
One of the hypotheses being considered regarding the cause of the stranding points to natural factors, such as disorientation caused by tides or the particular geography of the bay. “Bahía San Sebastián has very little slope and tides of more than 17 meters. If the orcas entered at high tide and it quickly receded, they could have become trapped,” detailed Mónica Torres, a technician from the park ranger team, on a local radio station.
Another natural factor being considered is climate change, which alters currents, temperature, and the availability of prey in the South Atlantic. Likewise, the possibility of some acoustic interference generated by vessels or sonars, which could have affected the orca’s echolocation system, is being investigated.
An unusual find: 26 dead orcas
What happened in Tierra del Fuego has several characteristics that are considered extraordinary. On one hand, it is a very uncommon variety of orca within the species.
The “ecotype D” shows distinctive morphological traits: a smaller postocular spot, a voluminous head, and a less prominent dorsal saddle. They mainly inhabit subantarctic waters, so their massive presence on the coasts of Tierra del Fuego is extremely atypical.
The other unusual characteristic is the high number of stranded specimens. In addition, globally, records of strandings of this specific ecotype are extremely scarce.
The first documented stranding of this type of specimens dates back to 1955, on the coast of New Zealand, where 17 animals were found. The second event took place in the Straits of Magellan and involved a total of 9 individuals.
