Abstract
Despite the presence of melon-headed whales in tropical and subtropical waters
worldwide, little is known about this species. To assess population structure in
Hawai‘i, dedicated field efforts were undertaken from 2000 to 2009. Using only
good quality photographs, there were 1,433 unique photo-identified individuals,
of which 1,046 were distinctive. Of these, 31.5\% were seen more than once.
Resighting data combined with social network analyses showed evidence of two
populations—a smaller, resident population, seen exclusively off the northwest
region of the island of Hawai‘i, and a larger population, seen throughout all the
main Hawaiian Islands (hereafter the “main Hawaiian Islands” population). A
Bayesian analysis examining the probability of movements of individuals between
populations provided a posterior median dispersal rate of 0.0009/yr (95\% CI =
0–0.0041), indicating the populations are likely demographically independent.
Depth of encounters with the Hawai‘i Island resident population was significantly
shallower (median = 381 m) than those with the main Hawaiian Islands population
(median = 1,662 m). Resightings of individuals have occurred up to 22 yr apart
for the Hawai‘i Island resident population and up to 13 yr apart for the main
Hawaiian Islands population, suggesting long-term residency to the islands for
both populations.
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