Pilot whales have repeatedly stranded themselves on beaches, especially in Australia and New Zealand, resulting in the deaths of several thousand animals in recent decades and frustrating their would-be rescuers. Now, the story has another twist, as a recent DNA analysis of 490 victims of 12 different stranding disasters has shown that mothers, calves, and other close relatives must have already been separated at the time the disaster occurred. The international team, which includes Oregon State University’s Scott Baker and University of Auckland’s Marc Oremus, recently published their results in The Journal of Heredity.
A 2012 mass stranding in New Zealand was particularly challenging because volunteers struggled to rescue 17 of 100 stranded animals that were still alive — only to have them turn around and re-strand themselves. To add to the frustration, that same beach had previously been the site of two other recent mass strandings. In one stranding, 18 of 25 pilot whales were rescued, but in the other stranding, 61 of the animals died.
Despite the name, pilot whales are not true whales. They’re actually large dolphins that can reach a size of up to 20 feet, meaning that it’s a difficult job to rescue even one stranded victim.
Pilot whales are considered a social deep-water species that tends to travel in large pods that can number as many as 100 animals. One theory of why they tend to get stranded on beaches is that if one youngster gets stranded, the concerned mother — and maybe the entire pod — will come to the rescue, resulting in the mass disaster.
However, the new genetic analysis revealed that the stranded pilot whales are not normal pods containing grandmothers, mothers, and calves. In fact, it showed that calves who were at an age where they would normally be dependent were widely separated from their mothers.
Scott Baker said that the DNA results mean that there’s something else happening to drive pilot whale families apart before the mass stranding occurs. Right now, science just doesn’t know what caused the deadly social disruption.
The next step? In addition to performing more genetic analysis to clarify relationships, the researchers want to place tracking devices on pilot whales that are returned to the ocean.
[swimming pilot whale photo courtesy SeaDave and flickr] [stranded whale photo courtesy Bahnfrend and Wikipedia Commons]