GENETIC IMPACT OF AN UNUSUAL GROUP MORTALITY AMONG HUMPBACK WHALES

Mass mortalities, due to infectious disease or toxic algal blooms, a,e known to have severe demographic impacts on marine mammal populations . The genetic impacts of these events, however, have received little a ttention. To investigate the genetic consequences of an unusual group mortality among humpback whales, we compared the mitochondrial DNA hap lotypes of 10 whales poisoned by mackerel contaminated with a dinoflag ellate neurotoxin to those of 32 live whales from the same regional po pulation. Two haplotypes that were rare in the reference sample of liv e whales accounted for eight of the 10 poisoned whales. A randomized t est of independence, based on 500 permutations of the data matrix, sho wed significant differences in the frequencies of haplotypes in the tw o samples (P <.002). This is the first demonstration that group mortal ity events in marine mammals can have unpredictable genetic consequenc es and points to a need to evaluate ecological disasters within the co ntext of the genetic mosaic of natural populations.