FOUR sperm whales were reported to have died Tuesday following a mass stranding on a beach on the northwestern tip of Sumatra, Indonesia.
A group of 10 sperm whales (Physeter macrocephalus) was spotted on Ujong Kareung beach in Aceh province on Monday morning, according to WWF-Indonesia, which has been monitoring attempts to rescue the animals.
Officials from the Navy, fisheries ministry and local government deployed teams and worked with residents and NGOs to try to push and tow the stranded whales back out into deeper water.
Two of the whales were reportedly injured, while the others risked suffocation and organ failure from being stuck in shallow waters for too long, according to Arman, a veterinarian from the Center for Wildlife Studies at the Syiah Kuala University in Banda Aceh, the provincial capital.
Seven whales were pushed back out into deeper water between Monday evening and early Tuesday morning, according to Whale Stranding Indonesia, a marine mammal conservation organisation based in Jakarta, which has also been monitoring the rescue. However, one of them returned to the beach.
By Tuesday afternoon, the four stranded whales were dead, according to WWF-Indonesia.
“We are coordinating with veterinarians to conduct a necropsy on the dead four whales,” the NGO said. “We are also using drones to monitor the six whales that survived.”
It is not yet clear why the whales swam so close to the shore, as the species is known to prefer open ocean with waters deeper than 1,000 meters (3,280 feet).
One theory is that the whales, which navigate by echolocation, were disoriented by seismic surveying activity, an offshore oil-and-gas exploration technique in which sound waves are blasted down to the seabed and the reflected waves used to provide information about the geology.
Three seismic surveys were reported to have taken place near the site where the whales were stranded, according to Stranded No More, a watchdog group with an interest in marine mammals.
The beaching of some 100 melon-headed whales in northwest Madagascar in 2008 was attributed in a 2013 report to acoustic stimuli from a survey vessel contracted by ExxonMobil.
The sound waves involved are typically 100,000 times more intense than a jet engine and can severely impact fish, dolphins, whales and sea turtles, causing temporary and permanent hearing loss, disrupting mating, and driving the animals into shallower water, where they risk getting stranded, according to oceans conservancy NGO Oceana.
The Jakarta Animal Aid Network (JAAN) acknowledged the possibility that a seismic survey may have been a factor in the stranding, but said there was little chance that this was the case in Aceh.
Another possibility, said Amang Raga of JAAN, involves the injured whales. He said sperm whales travel as a group, with the leader swimming out in front, and pod members were unlikely to abandon one another.
“So if one of the whales in the front becomes ill, the others will follow wherever it goes, and possibly [in this case it] swam close to the shore,” Amang said.
Sperm whales, which can grow to up to 20.5 meters (67 feet) in length, are listed as Vulnerable by the International Union for Conservation of Nature (IUCN).
This article was originally published on Mongabay.