Earthquakes may have been the root cause of the mass pilot whale stranding that was discovered last weekend on Anegada in the British Virgin Islands.
Although the cause has not been confirmed, a leading marine biologist working with others on the case, Antonio A. Mignucci-Giannoni, told the Source Thursday, “We think this socially-induced stranding event had to do with disorientation or perhaps auditory damage to the whales by underwater sound from the previously recorded earthquakes in the area days prior to the event.”
“Strandings” of cetaceans (whales, dolphins, and porpoises) are neither rare nor new, although human activity may have increased their frequency.
They occur when a marine animal is washed ashore or beaches itself and is unable to return to the sea. They may involve a single individual, a few animals, or scores of them. According to Wikipedia, there are upwards of 2,000 beached marine animals a year, and that’s just the ones that are discovered. Humans have been recording sightings of strandings for centuries, and there are archeological findings documenting one thousands of years ago.
The literature discusses numerous causes for strandings, including disease, starvation, injury, or exposure to pollution. Whales navigate by bouncing sound off of objects; if this echolocation system is tampered with or damaged by, say, underwater explosions or man-made sonar, it can confuse the animal. Because they are extremely social animals, researchers believe that sometimes healthy animals will follow an ailing fellow into the shallows.
Mignucci is a professor of marine sciences at the Inter-American University of Puerto Rico and at the Ross University School of Veterinary Medicine, director of the Caribbean Manatee Conservation Center, and founder of the Caribbean Stranding Network.
He and his team have been advising marine biologist Shannon Gore of Coastal Management Consulting BVI in handling the event, “particularly the documentation of the case and collection of samples for further analysis.” Other team members are Carla Rivera from the Caribbean Manatee Conservation Center, Susana Caballero, Universidad de Los Andes, Colombia, and Jeremy Kiska, Florida International University.
Mignucci said he was unable to get to Anegada to view the stranding firsthand, but the team reviewed video of the site and were able to count about 60 affected animals.
The internet publication Repeating Islands said Wednesday that more than 50 pilot whales had been beached on the sand or entangled in shoreline mangroves. It quoted the BVI Ministry of Natural Resources saying clean-up was underway and 30 to 40 whales had been buried and 17 towed out to sea. Initial estimates had put the number even higher, as much as 100.
Whatever the exact number, Mignucci said it is unusually high.
“I had dealt before with 25 whales,” he said, “but not 50-60-100.”
According to Repeating Islands, volunteers and non-profit groups assisted the BVI government in collecting tissue from 39 of the whales to be sent for analysis.
Mignucci said biologists will be studying the skin of the animals to determine the genetic structure of the population that was stranded and to determine their sex.
“If the tissues are good, we may be able to determine the diet of the whales from skin tissue. With the teeth, we will be attempting to age the whales using growth layer groups in the dentine/cement of the tooth,” he said.
“It may take a few months” to complete the analysis, he said.
Pilot whales, sometimes called “blackfish,” are a species of oceanic dolphins. There are two types: longfin and shortfin. They are quite similar, but short-finned pilot whales inhabit tropical waters while their cousins prefer cooler waters.
The shortfin pilot whale, the type beached in Anegada, ranges in length from about 18 feet (for adult females) to about 23.6 feet (for males).
For both types of whales, the average life span is 45 years for males and 60 years for females.