Melon-headed whale (Peponocephala electra)

Species >> Melon-headed whale (Peponocephala electra)

As awareness of the effects of anthropogenic noise on marine mammals has grown, research has broadened from evaluating physiological responses including injury and mortality to considering effects on behavior and acoustic communication. Most mitigation efforts attempt to minimize injury by enabling animals to move away as noise levels are increased gradually. Recent experiences demonstrate that this approach is inadequate or even counterproductive for small, localized marine mammal populations, for which displacement of animals may itself cause harm.

We assess the potential for population structure of melon-headed whales (Peponocephala electra) around the main Hawaiian Islands based on photo-identification data from 2002 through 2010, to help inform genetic analyses of population structure and interpretation of data obtained from satellite tags.

Of the 18 species of odontocetes known to be present in Hawaiian waters, small resident populations of 11 species—dwarf sperm whales, Blainville’s beaked whales, Cuvier’s beaked whales, pygmy killer whales, short-finned pilot whales, melon-headed whales, false killer whales, pantropical spotted dolphins, spinner dolphins, rough-toothed dolphins, and common bottlenose dolphins—have been identified, based on two or more lines of evidence, including results from small-boat sightings and survey effort, photo-identification, genetic analyses, and satellite tagging.

Movements of upper trophic level predators in an open ocean environment should be driven, in part, by the distribution, density, and movements of their prey. Surveys have shown that cetacean densities are higher closer to shore around the main Hawaiian Islands than in offshore waters (Barlow 2006), presumably reflecting increased productivity or spatial and temporal predictability of prey associated with island effects (Baird et al. 2008a).

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.