16 March 2013


Pilot whale stranding on Farewell Spit, South Island, New Zealand. Credit: Chagai via Wikimedia Commons.
Pilot whales that died in mass strandings in New Zealand and Australia included many unrelated individuals at each event——challenging a popular assumption that the whales follow each other to almost certain death on the beach because of family ties. This according to a new paper in the Journal of Heredity.

The researchers conducted genetic analyses of 490 individual pilot whales from 12 different stranding events and found multiple maternal lineages among the victims in each stranding. The bodies of mothers and young calves were often separated by large distances, and in many cases the mothers of calves were missing entirely from groups of whales that died in the strandings. This suggests that strong kinship bonds were disrupted prior to the actual stranding——and that these disruptions maybe played a role in triggering the strandings. Which challenges another popular hypothesis: that taking care of close maternal relatives may be the cause of otherwise healthy whales stranding.

The study has implications for people trying to save beached whales. "Rescue efforts aimed at refloating stranded whales often focus on placing stranded calves with the nearest mature females, on the assumption that [she] is the mother," says co-author Scott Baker, associate director of the Marine Mammal Institute at Oregon State University. "Our results suggest that rescuers should be cautious when making difficult welfare decisions——such as the choice to rescue or euthanize a calf——based on this assumption alone.

"It's usually assumed that environmental factors, such as weather or the pursuit of prey, bring pilot whales into shallow water where they become disoriented," says Baker. "Our results suggest that some form of social disruption also contributes to the tendency to strand. It could be mating interaction or competition with other pods of whales. We just don't know."

Whale warfare?

Interestingly long-finned pilot whales are the most common species to strand en masse worldwide and most of their beaching events are thought to be unrelated to human activity... unlike the strandings of some other species, which have been linked to the heinous noise of naval sonar and seismic exploration.
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