Hawaiian Islands False Killer Whale
The false killer whale (Pseudorca crassidens) is a large member of the dolphin family (the delphinids) found in tropical, subtropical and warm temperate waters worldwide. The name reflects a similarity with the shape of killer whale skulls, but the two species are not closely related genetically. The Main Hawaiian Islands (MHI) insular population is a small, discrete population, or stock, that lives exclusively in MHI nearshore waters. The number of false killer whales in this population has declined in recent decades, likely due to interactions with fisheries, to between 150 and 200 individuals. This population was listed as endangered under the Endangered Species Act (ESA) in 2012.
False killer whales are highly social animals that form social clusters, known as ’pods’, of related individuals that travel and forage together with no apparent lasting exchange among these clusters. Within pods, individuals may spread out over many miles when hunting, while smaller sub-groups spread apart and merge over periods of hours to days. The maximum age of false killer whales has been estimated to be over 50 years. While generally considered an open-ocean species, in addition to the insular population around the Main Hawaiian Islands, another insular population is found around the Northwestern Hawaiian Islands. These insular populations overlap with an open-ocean or pelagic population. The MHI insular population consists of four social clusters that occupy waters mostly within about 45 nautical miles of shore, although some individual members have been tracked as far as 71 nautical miles away from the islands. The Hawaiian pelagic population is found up to hundreds of miles from the archipelago, with groups occasionally approaching as close as roughly 7 nautical miles of the Main Hawaiian Island. The Northwestern Hawaiian Islands insular population lives within just under 60 nautical miles of the chain’s small islets and banks from Gardner Pinnacles (midway along the chain) to Kauai, with occasional excursions to the west side of Oahu in the MHI. Research indicates that these populations are largely demographically independent and that there is very little genetic interchange among them.
Numerous aerial-survey, photo-identification, satellite-telemetry, and genetic studies have made the MHI insular population the world’s most thoroughly studied population of false killer whales. Based on photo-identification studies, its current size is estimated to number between 150 and 200 whales (best estimate = 167), which is believed to be significantly fewer than were present in the late 1980s, when aerial surveys around the MHI sighted individual groups of false killer whales in excess of 400 individuals. The major known threat for this and other false killer whale populations in Hawaii is interactions with fisheries that lead to serious injuries or death.
What the Commission Is Doing
In 2009, the Commission recommended and supported actions by NMFS to list the MHI insular population of false killer whales as Endangered under the ESA. We also provided support for a study to compile and analyze related biological information. To reduce threats due to fishery interactions to the MHI insular population and other false killer whale populations in Hawaii, we also recommended that NMFS establish a Hawaiian False Killer Whale Take Reduction Team. In February 2010, NMFS established the team and charged it with preparing a plan to minimize false killer whale interactions with the Hawaii longline fisheries for tuna and swordfish. A representative of the Commission has been a member of the team since its inception. In November 2012, the NMFS listed the MHI insular population as Endangered under the ESA.
Commission Reports and Publications
See the false killer whale sections in chapters on Species of Special Concern in past Marine Mammal Commission Annual Reports to Congress.
Report prepared for the Marine Mammal Commission:
Baird, Robin W. 2009. A review of false killer whales in Hawaiian waters: biology, status and risk factors.
|Letter Date||Letter Description|
|January 2, 2018|
|July 10, 2014|
|October 1, 2012|
|February 17, 2010|
|February 4, 2010|
The most significant threat to false killer whales in Hawaii is interactions with fishing gear that lead to serious injury or death. False killer whales are attracted to fishing vessels, where they take (depredate) bait and hooked fish, such as mahi-mahi and yellowfin tuna. Consequently, they are sometimes caught on hooks or entangled in fishing lines. Such interactions with Hawaii-based longline fisheries have become a significant conservation issue for false killer whales within Hawaiian waters and on the high seas (in other words, within and beyond the U.S. Exclusive Economic Zone (EEZ) – shore to 200 nautical miles offshore).
To date, most documented interactions have involved the Hawaii pelagic population, because the fisheries operating within the range of the MHI insular population are not monitored. From 2003 to 2012, an average of approximately 12 deaths and serious injuries of pelagic false killer whales were estimated to have occurred within the EEZ per year. As early as 2008, when NMFS first recognized three stocks of false killer whales in Hawaii for management purposes, this rate of serious injuries and deaths was judged to be unsustainable by the pelagic stock. In 2010, the National Marine Fisheries Service (NMFS) formed a Take Reduction Team (TRT) to address the problem. The team quickly developed a Take Reduction Plan (TRP) that contained measures designed to mitigate those interactions. Since the implementation of the TRP in 2012, the estimated number of deaths and serious injuries has declined inside the EEZ to levels that are theoretically sustainable (roughly four per year from 2012 to 2015). However, deaths and serious injuries continue at high levels outside of the EEZ; these numbers are not factored into the assessment of whether the level of bycatch is sustainable or not. From 2008 to 2015, an average 14 false killer whales per year have been seriously injured or killed outside the EEZ. Twice, more than 35 false killer whales were estimated to have been seriously injured or killed outside the EEZ in a single year. Scientists are concerned that these numbers could be even higher due to under-reporting in the U.S. longline fishery, and to the presence of numerous foreign vessels that do not carry fishery observers. In 2018 and 2019, six false killer whales have been killed or seriously injured in the deep-set longline fishery operating inside the Hawaii EEZ. These animals most likely belonged to the pelagic stock, but there is a small chance that they could have come from the insular stock. Analyses of interactions data collected since the TRP was implemented in 2012 have indicated that the plan’s mitigation measures have largely failed to work. As of December 2018, the team is close to making consensus recommendations to NMFS that are designed to remedy the failure (see meeting notes).
MHI insular false killer whales are also vulnerable to fishery interactions. Few deaths or serious injuries resulting from fisheries interactions have been documented in this population, but accurate estimates of the number of fisheries interactions are not available because the inshore fisheries are not monitored. However, recent analyses of fishery-related wounds or scars along the mouth-line or on the dorsal fin, documented with photographs, suggest that the frequency of fishery interactions in the insular population occurs at an even higher rate than experienced by the pelagic population, and that the rate may be increasing. To reduce bycatch in the longline fishery of individuals from the MHI insular false killer whale population, the TRP recommended, and in 2012 NMFS implemented, a year-round closure of longline fishing within about 50 nautical miles of the MHI.
Current Conservation Efforts
Hawaiian Pelagic False Killer Whale Population
To reduce bycatch in the Hawaii pelagic population of false killer whales, the TRP includes measures requiring that longline fishermen use ‘weak circle hooks’ and ‘strong branch lines’, as well as certain handling techniques when a false killer whale is hooked. This configuration is designed to enable targeted tuna and swordfish to be caught, but allow the heavier, stronger false killer whales to straighten the hooks and escape. To date, this gear configuration has had mixed success. A few hooked whales have escaped, but in several cases branch lines broke or were cut. In these cases, hooks were likely to have been left embedded in the whales’ mouths or throats, with up to several yards of monofilament of potentially entangling line trailing from the hooks. Research indicates that whales released with embedded hooks and trailing line are likely to suffer serious injuries that are more likely than not to lead to death. On the 20% of vessel trips that have been observed, compliance with recommended handling techniques has been incomplete (e.g., cutting branch lines instead of applying tension until the hook straightens). Moreover, there is concern that compliance in the un-observed portion of the fleet may be poorer still. The TRT is addressing these issues, looking for ways to encourage the use of stronger branch lines, gathering more information on what happens when a whale is hooked, and improving the release methods used by longline boat crews. In addition, the TRT is considering the use of electronic monitoring to increase the proportion of the fleet that is monitored.
The TRP also includes a contingency measure that would close an area south of the MHI (southern exclusion zone – SEZ) if a certain threshold is met for pelagic population bycatch levels within the U.S. For the first time, in 2018, that threshold was met and exceeded when four whales were seriously injured or killed within the EEZ within one year. As a result, the fishery has been excluded from the SEZ from July 24th through the end of 2018.
In January 2019, a false killer whale was killed and another seriously injured within the EEZ, again triggering the closure of the SEZ. Because the SEZ has been closed two years in row, the area will not be reopened until one or more of the following criteria have been met:
- There have been no moralities or serious injuries within the EEZ for two years following the second closure;
- The number of moralities and serious injures does not exceed PBR for two years following the second closure;
- The average number of moralities and serious injuries for the most recent five years does not exceed PBR; or
- Upon consideration of the TRT’s recommendations and evaluation of all relevant circumstances, the Secretary of Commerce decides that reopening is warranted.
Main Hawaiian Island Insular False Killer Whale Population
After designating the MHI insular population as Endangered in November 2012, NMFS announced its intention to prepare a recovery plan to guide future research and management-recovery activities. In October 2016, NMFS held a meeting to gather information and ideas on actions to include in the recovery plan from false killer whale experts. Participants identified actions needed to monitor and improve information on the population’s status, mitigate threats, and establish measurable recovery criteria. Fishery interactions were identified as the insular population’s greatest threat, but participants also considered actions to assess and mitigate threats associated with contaminants and disease, noise, prey availability, and climate change. Most such actions focused on research to improve information on threats, rather than on mitigation actions, because data on the precise cause and magnitude of potential impacts is quite limited. NMFS is expected to release a draft recovery plan for public review and comment in early 2018, and the final plan is expected to be adopted later in 2018. In November 2017, NMFS published a proposal for designating critical habitat, with public comments due January 2nd, 2018. The Commission submitted comments supporting the proposed critical habitat designation, but noted that the proposed designation was overly broad. The Commission recommended that NMFS “undertake or support research needed to refine that designation by determining if there are specific areas that are essential to enabling the population to sustain itself in a healthy and productive state, to recover to the point where listing under the ESA is no longer warranted and, ultimately to reach its carrying capacity level.” The proposal identified certain areas used for energy production or military activities to be excluded from the critical habitat designation. The Commission did not completely agree with NMFS’ reasons for excluding some of the areas, and recommended that those areas be included in the critical habitat designation unless NMFS could provide a better justification.
The final Critical Habitat designation was announced in July 2018, and excluded three additional areas from the designation due to national security areas. These areas have been used only infrequently by false killer whales.
Because interactions documented by observers on longline boats within the range of the insular population are rare, it is thought that injuries in MHI insular false killer whales are due to commercial and recreational State fisheries that operate closer to shore. Currently there is no mechanism, such as an observer program, for collecting information of false killer whale interactions with State fisheries.
Selected Peer-Reviewed Publications
Revised stock boundaries for false killer whales (Pseudorca crassidens) in Hawaiian waters. AL Bradford, EM Oleson, RW Baird, CH Boggs, KA Forney, and NC Young. 2015. U.S. Department of Commerce, NOAA Technical Memorandum NOAA-TM-NMFS-PIFSC-47, 29pp
False killer whales and fisheries interactions in Hawaiian waters: Evidence for sex bias and variation among populations and social groups. RW Baird, SD Mahaffy, AM Gorgone, T Cullins, DJ McSweeney, EM Oleson, AL Bradford, J Barlow, and DL Webster. 2015. Marine Mammal Science 31(2): 579-590
What’s the catch? Patterns of cetacean bycatch and depredation in Hawaii-based pelagic longline fisheries. KA Forney, DR Kobayashi, DW Johnston, JA marchetti, and MG Marsik. 2011. Marine Ecology 32(3): 380-391
False whales (Pseudorca crassidens) around the main Hawaiian Islands: Long-term site fidelity, inter-island movements, and association patterns. RW Baird, AM Gorgone, DJ McSweeney, DL Webster, DR Salden, MH Deakos, AD Ligon, GS Schorr, J Barlow, and SD Mahaffy. 2008. Marine Mammal Science 24(3): 591-612