Daniel J. McSweeney’s research while affiliated with Universidad Autónoma de Baja California Sur and other places

Studies of short-finned pilot whales suggest they travel in stable mixed-sex groups composed of strongly associated individuals; however, temporal analyses of social structure are lacking. To examine site fidelity, association patterns, and temporal relationships, we analyzed data from 267 encounters of this species off the island of Hawai‘i from 2003 through 2007, identifying 448 distinctive individuals (68.1% seen more than once). About 72% of the whales were linked by association into a single social network, suggesting the possibility of multiple populations using the area. Sighting histories suggested that only some individuals exhibit high site fidelity. Individuals demonstrated preferential associations and community division was strongly supported by average-linkage hierarchical cluster analysis of the association data. Nine longitudinally stable social units composed of key individuals and their constant companions were identified. Qualitative assignment of age and sex classes of unit members indicated that some segregation between adult males and female/calf pairs may occur. Temporal analyses of individuals encountered on the same day indicate stable long-term associations. Differential patterns of residency and site fidelity were unexpected and may be indicative of multiple populations around the main Hawaiian Islands. The presence of a resident population demonstrating strong, long-term site fidelity and associations off Hawai‘i Island may warrant special management considerations.

False killer whales (Pseudorca crassidens) are large delphinids typically found in deep water far offshore. However, in the Hawaiian Archipelago, there are 2 resident island-associated populations of false killer whales, one in the waters around the main Hawaiian Islands (MHI) and one in the waters around the Northwestern Hawaiian Islands (NWHI). We use mitochondrial DNA (mtDNA) control region sequences and genotypes from 16 nuclear DNA (nucDNA) microsatellite loci from 206 individuals to examine levels of differentiation among the 2 island-associated populations and offshore animals from the central and eastern North Pacific. Both mtDNA and nucDNA exhibit highly significant differentiation between populations, confirming limited gene flow in both sexes. The mtDNA haplotypes exhibit a strong pattern of phylogeographic concordance, with island-associated populations sharing 3 closely related haplotypes not found elsewhere in the Pacific. However, nucDNA data suggest that NWHI animals are at least as differentiated from MHI animals as they are from offshore animals. The patterns of differentiation revealed by the 2 marker types suggest that the island-associated false killer whale populations likely share a common colonization history, but have limited contemporary gene flow.

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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.

We used mitochondrial and nuclear genetic markers to investigate population structure of common bottlenose dolphins, Tursiops truncatus, around the main Hawaiian Islands. Though broadly distributed throughout the world's oceans, bottlenose dolphins are known to form small populations in coastal waters. Recent photo-identification data suggest the same is true in Hawaiian waters. We found genetic differentiation among (mtDNA ΦST= 0.014–0.141, microsatellite F’ST= 0.019–0.050) and low dispersal rates between (0.17–5.77 dispersers per generation) the main Hawaiian Island groups. Our results are consistent with movement rates estimated from photo-identification data and suggest that each island group supports a demographically independent population. Inclusion in our analyses of samples collected near Palmyra Atoll provided evidence that the Hawaiian Islands are also occasionally visited by members of a genetically distinct, pelagic population. Two of our samples exhibited evidence of partial ancestry from Indo-Pacific bottlenose dolphins (T. aduncus), a species not known to inhabit the Hawaiian Archipelago. Our findings have important implications for the management of Hawaiian bottlenose dolphins and raise concerns about the vulnerability to human impacts of pelagic species in island ecosystems.

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). A number of high trophic level pelagic species have been shown to concentrate around and/or use mesoscale eddies as foraging habitat (e.g., Davis et al. 2002, Seki et al. 2002, Bakun 2006, Polovina et al. 2006, Yen et al. 2006). The islands, and their interaction with winds and currents, create a complex system of eddies that may also concentrate some prey types farther offshore (Seki et al. 2002), but whether island-associated cetacean populations use these offshore eddy systems for foraging habitat is unknown.

Movements and spatial use of Hawaiian insular false killer whales was examined using data from nine individuals satellite-tagged in 2009; five tagged off the island of O'ahu in October and four tagged off the island of Hawai'i in December. A total of 3,782 locations were available after filtering, over periods up to 104.8 days (median = 70.7 days), more than doubling the location data available from this population. Assessment of distance between pairs of individuals with overlapping data indicated we obtained movement information from at least five and possibly seven different social groups of false killer whales. All tagged individuals remained in association with the main Hawaiian Islands. While movements of one individual extended up to 112.8 km from shore, into a water depth of approximately 5,400 m, the average distance from shore ranged from about 11 to 23 km, in depths averaging about 500 to about 1,200 m. Four of the five individuals tagged off O'ahu moved west to Kaua'i and Ni'ihau, providing evidence the Hawaiian insular population uses the waters around the westernmost of the main Hawaiian Islands. There were no significant differences in the proportion of time spent using windward versus leeward sides of the islands. One individual that had been tagged previously (in 2008) showed very different spatial use patterns in 2008 versus 2009. Overall the data provides a more robust assessment of spatial use and movements of Hawaiian insular false killer whales that can be used in helping assess critical habitat if this population is listed under the Endangered Species Act.