WELLINGTON – Whales that beach themselves in large groups are not all members of the same family, a study has found, undermining long-held assumptions about the cause of mass strandings.
A team of scientists studied 12 mass beachings in Australia and New Zealand to examine the theory that healthy whales strand themselves while trying to help sick or disorientated family members who have run aground.
After examining the DNA of 490 whales they concluded the “care-giving model” did not stand up, as most of the whales were not related. Further, they found that many stranded calves were discovered with no mother nearby.
In the study, the position of each stranded whale was mapped to determine whether individuals found near each other were related. No correlation was found between location and kinship, even with nursing calves and their mothers, who were often widely separated when the group drove itself onto shore.
Coauthor Scott Baker from Oregon State University said the study, published in the Journal of Heredity, suggested the breakup of family groups in deep water might be a reason for mass strandings. The study suggested that disruptions prior to stranding could be due to feeding or mating competition, and even aggression among pods.
It speculated that distress calls from whales in trouble could create confusion among others in the vicinity, resulting in the separation of kin before they end up stranding themselves.
The researchers said the study had implications for attempts to refloat whales after they have stranded. “Often, stranded calves are refloated with the nearest mature females, under the assumption that this is the mother,” Baker said. “Unfortunately, the nearest female might not be the mother of the calf — our results caution against making rescue decisions based only on this assumption.”