Each year, more than a thousand marine mammals die during mass strandings, which are grisly events in which large numbers of whales or dolphins become beached on the shore together. But scientists still don’t know exactly why these strandings occur. Climatic events, unfamiliar underwater topography, and noise from seismic surveys and naval exercises have all been suggested to play a role. In another theory based on family ties, one or a few whales, driven by disease or starvation, veer off in the wrong direction and draw well-meaning family members into shallow, dangerous waters as they try to help.
However, a paper in this week’s Journal of Heredity suggests that the role of relatives in mass strandings may not be quite so straightforward.
The researchers collected skin samples and information about the spatial distribution of 490 long-finned pilot whales stranded in 12 events across New Zealand and Tanzania. By studying the whales’ mitochondrial DNA (a type of genetic information passed on from mother to offspring), the researchers could determine how closely-related the stranded animals were.