Despite their world‐wide distribution throughout the tropics and subtropics, false killer whales (Pseudorca crassidens) are one of the lesser‐known large odontocetes. Genetic evidence indicates a demographically isolated population around the main Hawaiian Islands. We examine site fidelity, movements and association patterns in this population using data from directed surveys and opportunistic photographs from 1986 to 2007. This species was only infrequently encountered, and while found in depths from 38 to 4,331 m, sighting rates were greatest in depths >3,000 m. We photo‐identified 152 distinctive individuals. Resighting rates were high, with an average of 76.8% of distinctive individuals within groups documented on more than one occasion. Most (86.6%) were linked by association into a single social network; only one large group (16 distinctive individuals), documented the farthest offshore (42–70 km), did not link by association to that large network, and may be part of an offshore population. Individual movements of up to 283 km were documented, with a large proportion of individuals moving among islands. Individuals were resighted up to 20.1 yr after first being documented, showing long‐term fidelity to the islands. Repeated associations among individuals were documented for up to 15 yr, and association analyses indicate preferred associations and strong bonds among individuals.
Although the Ziphiidae are the second‐most speciose family of cetaceans, information on beaked whale species and populations has been limited by the difficulties in finding and approaching free‐ranging individuals. Site fidelity, patterns of association, and movements of two species, Cuvier's (Ziphius cavirostris) and Blainville's (Mesoplodon densirostris) beaked whales, were assessed using a 21‐yr photographic data set from the west coast of the island of Hawaii. Resightings of individuals of both species spanned 15 yr, suggesting long‐term site fidelity to the area. Long‐term resightings were documented primarily from adult females of both species. Group sizes for both species were small and most groups had only a single adult male present. For Blainville's beaked whales, repeated associations between adult females and adult males were documented for all resightings of adult males over periods from 1 to 154 d. Among adult females, although repeated associations occurred up to 9 yr apart, individuals were seen separately in intervening years. Individuals of both species seen on multiple occasions were typically documented in multiple months/seasons, suggesting they may use the study area throughout the year. Such long‐term site fidelity has implications both for potential population structure and for susceptibility of beaked whale populations to anthropogenic impacts.
Beaked whales (family Ziphiidae) are thought to be among the longest and deepest diving mammals, and some species appear to be prone to mass-strand in response to high-intensity sonar. We studied diving behaviour of Cuvier’s ( Ziphius cavirostris G. Cuvier, 1823) and Blainville’s ( Mesoplodon densirostris (Blainville, 1817)) beaked whales in Hawaiian waters using suction-cup-attached time–depth recorders. Six whales, two Cuvier’s and four Blainville’s, were tagged and 41 h of dive data were collected. While Cuvier’s beaked whales were found in significantly deeper water depths (median depth = 2079 m) than Blainville’s beaked whales (median depth = 922 m), several aspects of diving were similar between the two species: (i) both regularly dove for 48–68 min to depths greater than 800 m (maximum 1408 m for Blainville’s and 1450 m for Cuvier’s); (ii) ascent rates for long/deep dives were substantially slower than descent rates, while for shorter dives there were no consistent differences; and (iii) both spent prolonged periods of time (66–155 min) in the upper 50 m of the water column. Based on time intervals between dives for the Cuvier’s beaked whales, such long dives were likely aerobic, but both species appeared to prepare for long dives by spending extended periods of time near the surface.
Management agencies often use geopolitical boundaries as proxies for biological boundaries. In Hawaiian waters a single stock is recognized of common bottlenose dolphins, Tursiops truncatus, a species that is found both in open water and near‐shore among the main Hawaiian Islands. To assess population structure, we photo‐identified 336 distinctive individuals from the main Hawaiian Islands, from 2000 to 2006. Their generally shallow‐water distribution, and numerous within‐year and between‐year resightings within island areas suggest that individuals are resident to the islands, rather than part of an offshore population moving through the area. Comparisons of identifications obtained from Kaua‘i/Ni‘ihau, O‘ahu, the “4‐island area,” and the island of Hawai‘i showed no evidence of movements among these island groups, although movements from Kaua‘i to Ni‘ihau and among the “4‐islands” were documented. A Bayesian analysis examining the probability of missing movements among island groups, given our sample sizes for different areas, indicates that interisland movement rates are less than 1% per year with 95% probability. Our results suggest the existence of multiple demographically independent populations of island‐associated common bottlenose dolphins around the main Hawaiian islands.
In the Pacific, rough‐toothed dolphins (Steno bredanensis) are typically found in the open ocean and in deep waters around oceanic islands. We examined habitat use, site fidelity, movements, and association patterns of this species in the main Hawaiian Islands. Sighting rates were highest in depths >1,500 m. There were frequent within‐ and between‐year resightings off the island of Hawai'i, indicating a small population size with high site fidelity. Resighting rates were lower off Kaua'i/Ni'ihau, indicating a larger population size, but with some site fidelity. Two individuals were documented moving from Kaua'i to Hawai'i, a distance of 480 km, but were not seen to associate with dolphins off Hawai'i. Observed movements were consistent with at most 2% dispersal per year between these two areas. Differences in group sizes, habitat use, and behavior imply that movements among the islands may be limited. Little is known about the diet of rough‐toothed dolphins in Hawai'i, but they are thought to feed primarily on near‐surface species. High fidelity to deep‐water areas off the island of Hawai'i likely reflects an increase in the predictability of prey associated with upwelling due to the island mass effect, wind stress curl and cyclonic eddies that form off the island.
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.
Migratory destinations of northeast Pacific humpback whales (Megaptera novaeangliae) were determined by repeat sightings of photographically identified individuals, using the black and white pigment patterns on the ventral side of the flukes. Individuals identified between 1975 and 1982 included 1056 in Hawaii, 420 in southeast Alaska, 54 in Prince William Sound, Alaska, 8 in British Columbia, and 12 in the Revillagigedo Islands, Mexico. Of these, 51 were found in Hawaii and southeast Alaska, 8 in Hawaii and Prince William Sound, 1 in Hawaii and British Columbia, and 1 in Mexico and Hawaii. Some travelled for four, five, and six successive seasons between Hawaii and southeast Alaska. One whale was found in British Columbia one summer and in southeast Alaska the next; the same individuals were commonly found off both Kona, Hawaii, and West Maui in winter. The study suggests that separate summer feeding areas may exist in the northeast Pacific where individuals prefer to feed. Migratory connections suggest that all humpbacks in the eastern North Pacific are of the same stock.
There are 2 recognized stocks of false killer whales Pseudorca crassidens in the US Exclusive Economic Zone surrounding Hawai'i, a small demographically isolated population around the main Hawaiian Islands and a larger offshore ('pelagic') population. Recent evidence suggests the insular population may have declined precipitously over the last 20 yr, and one possible contributing factor is interactions with offshore longline fisheries or other hook and line fisheries. To assess movements and habitat use, satellite tags were remotely deployed on individuals in 3 groups from the insular population and one from the offshore population. Although tagged off the leeward side of the island of Hawai'i, individuals from the insular population regularly moved to the windward sides of the islands. Some insular individuals moved extensively and rapidly among islands, while other individuals remained associated with the island of Hawai'i for extended periods before moving among the other islands. Comparisons of distances between tagged individuals indicated that individuals within groups disassociated and re-associated over periods of days, occasionally moving more than 100 km apart before re-associating. The offshore individual, tagged 123.8 km offshore, approached to within 62 km of land, inshore of the longline fishery exclusion boundary. The 3 insular groups moved a maximum of 83, 87 and 96 km offshore, respectively, indicating that the distance from shore cannot be used as a strict boundary between the populations, and that individuals from the insular population may overlap with the longline fishery. When combined with photo-identification the results suggest that boundaries between these 2 stocks should be revised.
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