Cooperative Conservation and Long-term Management of False Killer Whales in Hawaiʻi: Geospatial Analyses of Fisheries and Satellite Tag Data to Understand Fishery Interactions

False killer whales (Pseudorca crassidens) are long-lived upper trophic level odontocetes that are found throughout the tropics and sub-tropics. Until recently relatively little was known about this species anywhere in its range. Studies of this species originally begun around the main Hawaiian Islands in 1999 have provided the most detailed information on false killer whales anywhere in the world (Baird 2018a, 2018b). Three populations of false killer whales have been recognized in Hawaiian waters: an offshore (pelagic) population that ranges widely in the central tropical Pacific, and two insular populations, one around the northwestern Hawaiian Islands and one around the main Hawaiian Islands (MHI), with overlap of all three populations around Kauaʻi and Niʻihau (Baird et al. 2013; Bradford et al. 2015; Baird 2016). False killer whales from the main Hawaiian Islands insular population are known to eat a variety of pelagic and reefassociated game fish as well as squid (Baird 2016; Table 1), most of which are the target of commercial and recreational fisheries around the islands. False killer whale depredation of catch from fisheries around the islands has been documented for over 50 years. Pryor (1975) reported false killer whales taking catch off longlines off the Kona coast in 1963, and Shallenberger (1981) noted that depredation behavior “is very common in Hawaii where Pseudorca frequently steal tuna of up to 70 lbs., and sometimes take much larger fish.” Zimmerman (1983) described a group of false killer whales consuming most of an estimated 250 kilogram hooked Pacific blue marlin (Makaira mazara) off Kona in 1983.

Evidence that the MHI insular population was facing a variety of threats and appeared to have undergone a large-scale decline became apparent in the mid- to late-2000s (Baird and Gorgone 2005; Baird 2009; Reeves et al. 2009; Ylitalo et al. 2009). In response to a 2009 petition from the Natural Resources Defense Council to list this population under the Endangered Species Act (ESA), NOAA Fisheries convened a Biological Review Team in early 2010 to review the status of the population. That effort recognized that Hawaiian insular false killer whales should be considered a “Distinct Population Segment” (DPS) under the ESA and that this DPS was under threat of extinction (Oleson et al. 2010). Based on that review, NOAA Fisheries listed the DPS as endangered under the ESA in 2012. In 2014, NOAA Fisheries and the State of Hawaiʻi amended a cooperative agreement under section 6 of the ESA to include false killer whales, allowing the State and the federal government to work cooperatively toward conservation of this population. Under that cooperative agreement, in 2015 the State of Hawaiʻi received a Species Recovery Grant from NOAA Fisheries focusing on false killer whales, in order to fill data gaps and begin outreach efforts in local communities.

Cascadia Research Collective (CRC) has been undertaking research on false killer whales in Hawaiʻi since the early 2000s (Baird et al. 2005; Baird and Gorgone 2005). These studies, along with collaborating researchers from NOAA Fisheries and other organizations, have included estimation of abundance (Bradford et al. 2018), examination of social organization and stock structure (Chivers et al. 2007; Baird et al. 2012; Martien et al 2014, in press), assessment of evidence for fishery interactions (Baird et al. 2015, 2017), and examination of spatial use (Baird et al. 2010, 2012; Bradford et al. 2015), among other topics. Evidence for fishery interactions has primarily been indirect: individuals from this population have high levels of line injuries on the dorsal fin (Baird et al. 2015) and mouthline (Baird et al. 2017) that are consistent with being hooked in fishing gear. One of the other findings from these studies was the existence of discrete social clusters within the MHI insular population, representing long-term social units of highly-related individuals (Baird et al. 2012; Martien et al. 2014, in press), analogous to the highly-stable killer whale (Orcinus orca) “pods” documented along the west coast of North America (Baird 2000). The initial analysis recognizing these discrete social clusters identified several peripheral clusters that were pooled with the three main clusters (Baird et al. 2012), although it was unclear at the time of the analysis whether some or all of these peripheral clusters were sampling artifacts or represented real social entities. As the sample size of photographic identifications increased subsequent to those analyses, one of the three clusters was initially considered to be composed of two sub-clusters (Baird 2016), and later split with recognition of a fourth cluster (Mahaffy et al. 2017).

Collection of samples and photographic data for these studies has often been undertaken opportunistically, piggybacking work with false killer whales on field studies funded to work with other species (see Baird 2016) and benefiting from community-based science contributions (Bradford et al. 2018). Given their small population size (estimated at ~167 individuals in 2015, see Bradford et al. 2018) and a range that extends throughout the main Hawaiian Islands and as far as about 120 km from shore, sample sizes for analyses have been limited and subject to a variety of seasonal and geographic biases (see e.g., Baird et al. 2012; Bradford et al. 2018). Addressing these biases and limitations have been the focus of most of the directed research efforts with this population supported under the Species Recovery Grant obtained by the State of Hawaiʻi in 2015. Contracts from the State to CRC supported dedicated field efforts in areas with relatively limited sample sizes and at times of the year when information was lacking, as well as analyses of data obtained during those efforts, which were combined with existing CRC photographic and satellite tag data sets. This report summarizes field efforts and the results of these analyses.

Developing solutions to marine mammal bycatch in fisheries is challenging at the best of times. In the U.S., when bycatch is known to exceed a population’s Potential Biological Removal (PBR) level (Wade 1998), Take Reduction Teams can be formed to bring fishermen, scientists, conservationists and managers together to develop ways to reduce bycatch (Young 2001). Determining whether bycatch exceeds the PBR level requires information both on population abundance and on bycatch rates, the latter usually obtained through fishery observer programs. When there are no observer programs to determine bycatch rates, as is the case for nearshore fisheries in Hawaiʻi, managing fishery bycatch is much more complicated, in part because fishermen are often unwilling to recognize that a bycatch problem exists in the first place.

In the case of the endangered MHI insular population of false killer whales, getting fishermen to recognize that there may be a bycatch issue has been a slow process for a number of reasons. Most importantly, there are a large number of commercial and recreational fishermen around the main Hawaiian Islands (Pooley 1993; McCoy et al. 2018), while the false killer whale population is small (Bradford et al. 2018), so any one fisherman may only infrequently encounter false killer whales. Compounding this problem are three other similar looking species of “blackfish” around the islands that are both more abundant than and often confused with false killer whales (Carretta et al. 2019; Yahn et al. 2019), leading to a common distrust of the false killer whale abundance estimates.

Discussions with fishermen regarding false killer whale bycatch in nearshore fisheries in Hawaiʻi have been occurring in a variety of venues since information emerged that individuals from the main Hawaiian Islands population have relatively high levels of fishery-related injuries (Baird and Gorgone 2005; Baird et al. 2015, 2017). These discussions have included annual meetings of the Pacific Scientific Review Group — an advisory body to NOAA Fisheries; various meetings of the Western Pacific Regional Fishery Management Council and its advisory bodies; a recovery-planning workshop held by NOAA Fisheries in Honolulu in October 2016; and the annual meeting of the Marine Mammal Commission in Kona in May 2019. Fishermen at these meetings have often commented that they’ve never had interactions with false killer whales and expressed their belief that depredation by or bycatch of false killer whales in nearshore fisheries in Hawaiʻi rarely, if ever, occurs.

The ultimate goals of this effort are to understand what factors influence spatial use and movement patterns of false killer whales, and how they overlap and potentially interact with nearshore fisheries around the main Hawaiian Islands. Since spatial use varies by social cluster (Baird et al. 2012), which may also influence the probability of interacting with fisheries (Baird et al. 2015), we first use the updated full CRC photo-identification catalog to re-assess social clusters within the main Hawaiian Islands insular population. To examine overlap and potential interactions with fisheries, we characterize both false killer whale satellite tag data (Baird et al. 2012) and the spatial and temporal trends in nearshore commercial fisheries using data from the state’s Commercial Marine Licensing (CML) reporting system. Fishermen who sell their catch in Hawaiʻi are required to have a CML and have mandatory reporting requirements for catch and effort in commercial fisheries statistical areas. We use data from these fishing reports for 2007 through 2017, a period that overlaps with almost all of the satellite tag data available for the main Hawaiian Islands insular population of false killer whales (2007-2018). We then combine these two data streams (false killer whale satellite tag data and information on fishing effort) to identify areas where individual fishermen are most likely to interact with false killer whales. In particular, we develop fishery overlap indices to assess the relative probability of an individual fisherman having false killer whales in their area when fishing. Such indices should allow for identifying which fishermen likely have the highest interaction rates, and thus may be the most qualified for assisting in the development of solutions to the depredation and bycatch issue. Finally, we explore movement patterns of false killer whales in relation to environmental variables to attempt to assess what factors play the greatest role in describing and understanding their spatial use. Combined these efforts are meant to contribute to ongoing efforts to create a recovery plan and implement recovery actions for this endangered population.


Baird, R.W., D.B. Anderson, M.A. Kratofil, D.L. Webster, and S.D. Mahaffy. 2019. Cooperative Conservation and Long-term Management of False Killer Whales in Hawaiʻi: Geospatial Analyses of Fisheries and Satellite Tag Data to Understand Fishery Interactions. Report to the State of Hawaiʻi Board of Land and Natural Resources, under Contract No. 67703.

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