Sabre D. Mahaffy

Short Note: Open-Ocean Movements of a Satellite-Tagged Blainville’s Beaked Whale (Mesoplodon densirostris): Evidence for an Offshore Population in Hawai‘i?

Abstract : In Hawaiian waters, a single stock of Blainville s beaked whale (Mesoplodon densirostris) is recognized, extending throughout the U.S. Exclusive Economic Zone (EEZ) surrounding the archipelago and into adjacent international waters (Carretta et al., 2011). Abundance within the entire EEZ around Hawai i was estimated at 2,872 individuals based on a large vessel sighting survey (Barlow, 2006), with a single on-effort sighting near the western boundary of the EEZ (Hamilton et al., 2009). There is, however, considerable uncertainty associated with this estimate (CV = 1.17; Barlow, 2006), and there is recent evidence that individuals documented around the main Hawaiian Islands may not be part of an open-ocean population (McSweeney et al., 2007; Schorr et al., 2009). Individual Blainville s beaked whales instrumented with satellite tags off the island of Hawai i have remained strongly associated with the island, primarily using slope habitats for the entire duration of satellite tag transmissions (up to 71 d; Schorr et al., 2009). Schorr et al. (2009) noted a mean distance from shore of 16.9 km (range 4.4 to 27.7 km) and a mean depth of 1,156 m (range 880 to 1,455 m) for six satellite tagged individuals, over periods ranging from 15 to 71 d (median = 43 d), with from 26 to 405 locations per individual (median = 195 locations/ individual). Although these individuals moved a cumulative distance of at least 8,000 km over the duration of their tag attachments, median distances of locations from the tagging location for the different individuals ranged from 19.9 to 91.8 km, and the maximum distance any individual moved from where it was tagged was only 139 km (Schorr et al., 2009). Combined with long-term resightings of distinctive individuals off the island (McSweeney et al., 2007), such results suggest the existence of an island-resident population.

5. Biologically Important Areas for Cetaceans Within U.S. Waters – Hawai‘i Region

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, melonheaded 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. In this review, we merge existing published and unpublished information along with expert judgment for the Hawai‘i region of the U.S. Exclusive Economic Zone and territorial waters in order to identify and support the delineation of 20 Biologically Important Areas (BIAs) for these small and resident populations, and one reproductive area for humpback whales. The geographic extent of the BIAs in Hawaiian waters ranged from approximately 700 to 23,500 km. BIA designation enhances existing information already available to scientists, managers, policymakers, and the public. They are intended to provide synthesized information in a transparent format that can be readily used toward analyses and planning under U.S. statutes that require the characterization and minimization of impacts of anthropogenic activities on marine mammals. Odontocete BIAs in Hawai‘i are biased toward the main Hawaiian Islands and populations off the island of Hawai‘i, reflecting a much greater level of research effort and thus certainty regarding the existence and range of small resident populations off that island. Emerging evidence of similar small resident populations off other island areas in Hawaiian waters suggest that further BIA designations may be necessary as more detailed information becomes available.

Familial social structure and socially driven genetic differentiation in Hawaiian short-finned pilot whales

Social structure can have a significant impact on divergence and evolution within species, especially in the marine environment, which has few environmental boundaries to dispersal. On the other hand, genetic structure can affect social structure in many species, through an individual preference towards associating with relatives. One social species, the short‐finned pilot whale (Globicephala macrorhynchus), has been shown to live in stable social groups for periods of at least a decade. Using mitochondrial control sequences from 242 individuals and single nucleotide polymorphisms from 106 individuals, we examine population structure among geographic and social groups of short‐finned pilot whales in the Hawaiian Islands, and test for links between social and genetic structure. Our results show that there are at least two geographic populations in the Hawaiian Islands: a Main Hawaiian Islands (MHI) population and a Northwestern Hawaiian Islands/Pelagic population (FST and ΦST p < .001), as well as an eastern MHI community and a western MHI community (FST p = .009). We find genetically driven social structure, or high relatedness among social units and clusters (p < .001), and a positive relationship between relatedness and association between individuals (p < .0001). Further, socially organized clusters are genetically distinct, indicating that social structure drives genetic divergence within the population, likely through restricted mate selection (FST p = .05). This genetic divergence among social groups can make the species less resilient to anthropogenic or ecological disturbance. Conservation of this species therefore depends on understanding links among social structure, genetic structure and ecological variability within the species.