Marine Mammal Commission

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 just less than 170 individuals. This population was listed as endangered under the Endangered Species Act (ESA) in 2012.

False killer whales

False killer whales, October 15, 2010. (Robin Baird, Cascadia Research, NMFS Permit # 731-1774)

Species Status

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 seven 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 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

The Commission has been an active member of the False Killer Whale Take Reduction Team (FKWTRT) since its inception in 2010. This multi-stakeholder team makes recommendations to NMFS on the development and refinement of the False Killer Whale Take Reduction Plan (FKWTRP).

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.

In 2019, the Commission held its annual meeting in Hawaii, and dedicated one session to understanding the current status of interactions between pelagic false killer whales and the deep-set longline fishery, and between insular false killer whales and State managed hook-and-line fisheries (see session summaries).

In December 2020, the Commission commented on NMFS’s proposed Recovery Implementation Strategy for the insular population. The Commission recommended that the Strategy address the relative urgency of different measures, identify necessary resources and collaborations, and prioritize the monitoring of state commercial and recreational fisheries with the potential to interact with insular false killer whale.

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.

Commission Letters

Letter Date Letter Description
December 18, 2020

Letter to NMFS regarding its proposed Recovery Implementation Strategy for insular false killer whales

January 2, 2018

Letter to NMFS on a proposed critical habitat designation for MHI Insular false killer whales

July 10, 2014

Letter to NMFS on an incidental harassment permit for Hawaii long line fisheries takes of MHI false killer whales

October 1, 2012

Letter to NMFS on a proposed rule to list MHI Insular false killer whales as endangered

February 17, 2010

Letter to NMFS on the formation and meeting of the False Killer Whale Take Reduction Team

February 4, 2010

Letter to NMFS on actions to establish a take reduction team and take reduction plan for false killer whales in Hawaii

Learn More


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 longline 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).

Because fisheries operating with the range of the insular populations are not monitored, documented interactions have involved only the pelagic population. From 2003 to 2012, an average of approximately 11 serious injuries and deaths 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, it assessed this rate of serious injuries and deaths as unsustainable by the pelagic stock. In 2010, the National Marine Fisheries Service (NMFS) formed the FKWTRT to address the problem. Within a year, the team  recommended a suite of regulatory and non-regulatory measures, which became the FKWTRP . Following the implementation of the TRP in 2012, the estimated average number of deaths and serious injuries declined inside the EEZ by over half to 5.4 per year for the years 2013-2017. However, since then the bycatch rate inside the EEZ has increased by over three-fold to an average of 17.2 per year from 2018-2022.  Furthermore, deaths and serious injuries continue at high levels outside of the EEZ. From 2002 to 2013, an average just over eight false killer whales were seriously injured or killed outside the EEZ each year. However, in recent years (2014-2022), the bycatch rate outside the EEZ the rate has jumped five-fold to 40.2 per 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. From 2018-2021, at least 86 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. In late 2018, the team was close to making consensus recommendations to NMFS designed to remedy the failure (see meeting notes), however little progress has been made since. Following a hiatus during the COVID pandemic, the TRT reconvened in 2022 and 2023 to re-examine mitigation options that have the potential to substantially reduce mortalities and serious injuries due to interactions with longline gear.

The increases in mortalities and serious injuries have likely resulted from increases in the size of the fishery and the vulnerability of the whales to interactions with the longline gear. Since 2010, the size of the fishery increased by 20 percent from 122 to 147 permitted vessels in 2022. In addition, over the same period fishermen have increased the number hooks fished per set of the gear by 36 percent from roughly 2,200 to 3,000 hooks per set. In combination, these and other changes have increased the size of the resource available to false killer whales, catch and bait on hooks, by 90 percent. In 2010, the fishery put just over 33 million hooks in the water, but in 2023 that number had grown to over 63 million, The increase has averaged an additional 2.3 million hooks every year. Further, the likelihood that a false killer whale has an interaction with longline gear that results in death or serious injury has increased over the same period. Outside the EEZ, bycatch per unit effort (BPUE) increased from an annual average of 1.5 mortalities and serious injuries per 10 million hooks from 2010 to 2013 to 7.0 from 2014 to 2022. Inside the EEZ, BPUE declined from 3.9 per 10 million hooks in 2010 to zero in 2015, but increased subsequently to an average of 2.9 form 2019-2022.

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 meters of monofilament of potentially entangling line trailing from the hooks. Research indicates that odontocetes 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) for the remainder of the calendar year if a certain threshold is met for pelagic population bycatch levels within the U.S. For the first time, in 2018, the threshold at the time of two mortalities or serious injuries was met and exceeded when four whales were seriously injured or killed within the EEZ within one year. As a result, the fishery was 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 was closed two years in row, the area could not be reopened until one or more of the following criteria were met:

  1. There have been no moralities or serious injuries within the EEZ for two years following the second closure;
  2. The number of moralities and serious injures does not exceed the stock’s potential biological removal level (PBR) for two years following the second closure;
  3. The average number of moralities and serious injuries for the most recent five years does not exceed PBR; or
  4. Upon consideration of the TRT’s recommendations and evaluation of all relevant circumstances, the Secretary of Commerce decides that reopening is warranted.

In 2020, NMFS published a new, larger estimate of the size of the pelagic false killer whale stock. The five-year average annual mortality and serious injury rate did not exceed the new PBR, which is based on stock size. Consequently, the third criterion was met, and in August, 2020, NMFS reopened the EEZ. Following a stock-size update in 2020, the trigger to close the SEZ increased from two to four mortalities and serious injuries. In 2021, three mortalities and serious injuries occurred within the EEZ between mid-January and mid-April, and then a fourth interaction occurred in November. However, the determination that the interaction resulted in a serious injury was not made until after the end of the year, and consequently the SEZ was not closed, which made it clear that the closure policy needs to be revised.

In late 2022 and early 2023, the TRT met to recommend new management/mitigation measures that would finally to reduce mortality and serious injury to levels less than PBR.  However, the team could not reach consensus, which left NMFS with the responsibility for amending the TRP using the ideas generated by the team and the recommendations from factions within the team. Proposed mitigation measures included reducing the amount of fishing taking place (effort reductions) and further modifications to the gear and fishing practices. NMFS is expected to publish proposed amendments to the TRP in 2024.

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. In October 2020, NMFS released a draft recovery plan and implementation strategy for public review and comment. Commission comments, submitted in December 2020, included recommendations that NMFS: 1) better align the implementation strategy with the recovery plan, 2) focus of those actions that can be practicably implemented immediately, 3) provide details on how resources necessary to implement the recovery plan will be secured, 4) prioritize the monitoring of commercial and recreational fisheries that could be taking insular false killer whales. NMFS published the final recovery and implementation plans in November 2021.

In November 2017, NMFS published a proposal for designating critical habitat. The Commission submitted comments generally supporting the proposal, but noted that it 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 fully 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, which was announced in July 2018, excluded three additional areas from the designation due to national security concerns, and an assessment that the areas are used only infrequently by false killer whales.

Because interactions documented by observers on longline vessels 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.

Additional Resources

General Information

NMFS False Killer Whale species page

NMFS 2020 Stock Assessment Reports – False Killer Whale

IUCN Red List – False Killer Whale

Wikipedia – False killer whale

Cascadia Research Collective – False Killer Whales in Hawaii

The Lives of Hawaii’s Dolphins and Whales: Natural History and Conservation. RW Baird. 2016. University of Hawaii Press, Honolulu

False Killer Whale. In: Encyclopedia of Marine Mammals, 3rd Edition. Edited by Bernd Würsig et al. 2018. Elsevier.

Selected Peer-Reviewed Publications

Patterns of depredation in the Hawai’I deep-set longline fishery informed by fishery and false killer whale behavior. Joseph E Fader, RW Baird, AL Bradford, DC Dunn, KA Forney and AJ Read. 2021. Ecosphere

Is it all about the haul? Pelagic false killer whale interactions with longline fisheries in the central North Pacific. David Anderson, RW Baird, AL Bradford, and EM Olsen. 2020. Fisheries Research 230:105665.

Abundance estimates of false killer whales in Hawaiian waters and the broader central Pacific. Amanda L Bradford, EA Becker, EM Oleson, KA Forney, JE Moore, and J Barlow. 2020. NOAA Technical Memorandum NOAA-TM-NMFS-PIFSC-104, 78 p.

Abundance estimates for management of endangered false killer whales in the main Hawaiian Islands. Amanda L. Bradford, RW Baird, SD Mahaffy, AM Gorgone, DJ McSweeney, T Cullins, DL Webster, AN Zerbinia. 2018. Endangered Species Research 36:297-313.

Revised stock boundaries for false killer whales (Pseudorca crassidens) in Hawaiian waters. Amanda L Bradford, EM Oleson, RW Baird, CH Boggs, KA Forney, and NC Young. 2015. 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. Robin W 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. Karin A Forney, DR Kobayashi, DW Johnston, JA marchetti, and MG Marsik. 2011. Marine Ecology 32(3): 380-391.

Evidence of a Possible Decline since 1989 in False Killer Whales (Pseudorca crassidens) around the Main Hawaiian Islands. Randall R Reeves, S Leatherwood, and RW Baird. 2009. Pacific Science 63(2): 253-261.

False whales (Pseudorca crassidens) around the main Hawaiian Islands: Long-term site fidelity, inter-island movements, and association patterns. Robin W 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