Field Studies and Analyses from 2020 through 2022 to Support the Cooperative Conservation and Long-Term Management of Main Hawaiian Islands Insular False Killer Whales

In 2012 the main Hawaiian Islands (MHI) insular population of false killer whales (Pseudorca crassidens) was listed as endangered under the U.S. Endangered Species Act (ESA). Language in the ESA encourages federal cooperation with States, and provides a mechanism for funding support for States to aid in conservation of endangered species (referred to as Section 6 grants). Supported by NOAA Fisheries Section 6 grants received by the State of Hawaiʻi, Cascadia Research Collective (CRC) was contracted in 2016 and again in 2020 to assist with these efforts, undertaking field studies and analyses related to this population of false killer whales. Here we report on the outcome of those efforts from 2020 through 2022, and also include results from field activities during this period supported by other funding sources.

Pandemic-related travel restrictions imposed shortly after the contract was issued led CRC to begin ‘rapid response’ efforts off Hawaiʻi Island when false killer whales were reported or when working conditions were particularly suitable for working offshore or in northern parts of the study area, where encounter rates with false killer whales are higher. After travel restrictions had eased, CRC resumed typical multi-week intensive field efforts in December 2020, but continued a combination of rapid response and multi-week field efforts through the end of the contract.

Over the three-year period CRC had 30 encounters with MHI insular false killer whales and obtained identification photos of 110 unique individuals (approximately two-thirds of the estimated population). Of these 30 encounters, 19 were from rapid-response efforts and 11 were from directed field projects. One-third of CRC encounters were of groups that were re-found by tracking individuals that had been satellite-tagged in a previous encounter. Near real-time information from tagged animals was also provided to researchers with the Pacific Whale Foundation (PWF), resulting in the contribution of three additional encounters in the Maui Nui area. When combined with photo contributions from PWF and other researchers as well as community science contributors, a total of 145 unique individuals were identified from 86 encounters over the three-year period. Of these, 10 had not been previously documented, with nine of the 10 individuals considered not distinctive or slightly distinctive, suggesting slow recruitment to the population through births rather than the discovery of new social groups.

Photo-identification data from 2020 and 2021 were combined with identifications available from 1999 through 2019 in an analysis to identify the number and membership of social clusters. This analysis showed there are four discrete social clusters within the population, and a manuscript describing these analyses and results was submitted for publication (Mahaffy et al. in review). Photo-identification data from 2020 and 2021 were also provided to researchers at the Pacific Islands Fisheries Science Center (PIFSC) for ongoing analyses to estimate abundance and population trends spanning 1999 through 2021.

Location data were obtained from 16 LIMPET (Low-Impact Minimally-Percutaneous External-electronics Transmitter) satellite tag deployments, including individuals from all four social clusters. Data from these deployments were combined with tag data from 2007-2019 to examine spatial use by cluster. As was the case with earlier analyses, results showed cluster-specific spatial use. Although there is overlap of all four social clusters, particularly off windward waters of Maui and Molokaʻi, clusters varied in their spatial use by distance from shore, in relation to seafloor depth, and in terms of the proportion of time they spent in windward or leeward waters around the islands. Location data were also provided to PIFSC to estimate cluster-specific capture probabilities for the ongoing abundance estimation effort.

Between 2020 and 2022, 28 skin and blubber biopsy samples were obtained, including samples from all four clusters. Sub-samples of all were provided to the University of Hawaiʻi Health and Stranding Lab for ongoing analyses of blubber histology and hormone chemistry. Eighteen of the samples were from individuals that had not been previously biopsied (all from Clusters 3 and 4); skin subsamples of these were sent to the Southwest Fisheries Science Center to determine sex and mitochondrial haplotype and incorporated into a larger analysis of sex and haplotype distribution by social cluster presented by Mahaffy et al. (in review).

Overall, results obtained over this three-year period will allow for more robust estimation of population abundance and trends, as well as characterization of population health, spatial use, and age and sex makeup of the population.


Baird, R.W., C.J. Cornforth, S.D. Mahaffy, J.K. Lerma, A.E. Harnish, and M.A. Kratofil. 2023. Field Studies and Analyses from 2020 through 2022 to Support the Cooperative Conservation and Long-Term Management of Main Hawaiian Islands Insular False Killer Whales. Report to the State of Hawai‘i Board of Land and Natural Resources under Contract No. 68819.

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