Genetic impact of an unusual group mortality among humpback whales.

Mass mortalities, due to infectious disease or toxic algal blooms, are known to have severe demographic impacts on marine mammal populations. The genetic impacts of these events, however, have received little attention. To investigate the genetic consequences of an unusual group mortality among humpback whales, we compared the mitochondrial DNA haplotypes of 10 whales poisoned by mackerel contaminated with a dinoflagellate neurotoxin to those of 32 live whales from the same regional population. Two haplotypes that were rare in the reference sample of live whales accounted for eight of the 10 poisoned whales. A randomized test of independence, based on 500 permutations of the data matrix, showed significant differences in the frequencies of haplotypes in the two samples (P < .002). This is the first demonstration that group mortality events in marine mammals can have unpredictable genetic consequences and points to a need to evaluate ecological disasters within the context of the genetic mosaic of natural populations.