Range and primary habitats of Hawaiian insular false killer whales: informing determination of critical habitat

Abstract

For species listed under the US Endangered Species Act, federal agencies must designate 'critical habitat', areas containing features essential to conservation and/or that may require special management considerations. In November 2010, the National Marine Fisheries Service proposed listing a small demographically isolated population of false killer whales Pseudorca crassidens in Hawai`i as endangered but has not yet proposed designating critical habitat. We assesssed the population's range and heavily used habitat areas using data from 27 satellite tag deployments. Assessment of independence of individuals with temporally overlapping data indicated that data were from 22 'groups'. Further analyses were restricted to 1 individual per group. Tag data were available for periods of between 13 and 105 d (median = 40.5 d), with 8513 locations (93.4% from July - January). Analyses of photo-identification data indicated that the population is divided into 3 large associations of individuals (social clusters), with tag data from 2 of these clusters. Ranges for these 2 clusters were similar, although one used significantly deeper water, and their high-use areas differed. A minimum convex polygon range encompassing all locations was ~82800 km2, with individuals ranging from Ni`ihau to Hawai`i Island and up to 122 km offshore. Three high-use areas were identified: (1) off the north half of Hawai`i Island, (2) north of Maui and Moloka`i and (3) southwest of Lana`i. Although this analysis provides information useful for decision-making concerning designation of critical habitat, there are likely other high-use areas that have not yet been identified due to seasonal limitations and availability of data from only 2 of the 3 main clusters.