Lethal Removal Of Aggressive Hawaiian Monk Seals On Kure Atoll

August 10, 2011

NOAA Fisheries staff are saddened by these events and acknowledge that the lethal removal of an endangered species is a severe action. However, NOAA Fisheries has determined that at least one adult male seal and possibly two should be lethally removed from Kure Atoll in the Northwestern Hawaiian Islands (NWHI). After exhausting all available options under the Endangered Species Act (ESA), NOAA believes this action is necessary for the long-term survival of the species. While every animal is precious in a population that continues to decline, concern for the overall species needs to be a priority. Not taking action at this time would put these pups, juveniles and those born in the future at continued risk.


Hawaiian monk seals are declining in the NWHI, largely due to low juvenile survival. The primary cause of mortality of young animals appears to be food limitation; however shark predation, entanglement in marine debris and male aggression also contribute to losses of young seals.

Male aggression is typically categorized as either involving single or multiple males. These appear to be two distinct phenomena in terms of the male behavior and the age/sex of victims. Multiple-male aggression involves several adult males simultaneously competing to mate with a single seal, typically an adult female (although younger animals and males can be victimized in some cases). This can lead to severe traumatic wounds and death. Single-male aggression involves one male harassing, mounting and biting a young seal, typically a recently weaned pup of either sex. In the process, the victim may be drowned or sustain bite wounds that subsequently become infected and lead to debilitation or death.

Aggressive interactions between male seals (of a variety of species, not just monk seals) and smaller animals is normal, and often lead to scratches and relatively minor bite wounds. However, single male aggression in seals becomes a particular concern when the perpetrator displays an aberrant focus on young animals, with frequent, repeated and severe aggressive behavior that threatens their survival. This is highly unusual behavior amongst monk seals in Hawaii and cannot be well explained, but previous experience shows that the impact of such aggression on smaller seals can be considerable.

For context, the Kure Atoll monk seal population was estimated to be comprised of 100 individuals in 2010, including 18 pups, 23 juveniles and sub-adults, 30 adult females and 29 adult males. This subpopulation’s abundance fell precipitously from 2001 to 2004, and subsequently partially recovered. Given the low population size, low pup production and precarious status of this subpopulation, any mitigation in losses of young animals could have significant positive population level effects.

2011 Kure Field Season

In Spring/Summer 2011, male aggression became pronounced once pups began weaning at Kure Atoll. To date, 17 pups have been born in 2011. Three pups disappeared in March and April and it is not known whether these pups weaned and then disappeared or if they were somehow lost prior to weaning. One of these three pups was later found badly decomposed, such that cause of death could not be determined. We cannot rule out male aggression as a contributor to these mortalities given the pattern of aggression that was seen late in 2010 and early in 2011.

Of the remaining 14 pups, one is still nursing. The other 13 have weaned, and 10 of them have been victims of male aggression, sustaining injuries. Two of the injured pups developed severe wounds over time and have not been seen since early June. They are presumed dead as a result of male aggression. In addition, at least three juvenile seals have been attacked by adult males and suffered injuries.

Two males (KE18 and KO42) have been identified as the aggressors. They have been observed attacking newly weaned and juvenile seals, causing injuries including lacerations, scratches and puncture wounds ranging in severity:

  • KE18, a nine-year-old male, has been observed by NOAA Fisheries staff stationed at Kure Atoll behaving aggressively toward nine individuals on seven occasions between May 24 to July 28 by harassing, mounting, scratching, or chasing pups or holding them underwater. On another seven occasions, KE18 made directed approaches towards pups but field staff intervened in these instances to prevent additional harm. KE18 was also observed displaying “extreme aggression” towards one pup in 2010. The severity and frequency of his observed aggression increased in 2011. KE18 was observed in aggressive encounters with both of the weaned pups that eventually developed severe injuries and disappeared.
  • KO42, a five-year-old male, has been observed to be aggressive toward four individuals on five occasions between May 31 and June 19 by biting, harassing, mounting, scratching, or chasing pups or holding them underwater. On another four occasions, KO42 made directed approaches towards pups but field staff intervened in these instances to prevent additional harm. This is the first field season staff have observed KO42s direct aggression towards pups. Two of the victims injured were also observed being attacked by KE18.

Migration Undertaken To Date

Once the frequency and severity of injuries was noted, field staff engaged in activities designed to mitigate further harm. To protect pups from immediate threats from males and to also discourage the males from future interactions with pups, KE18 and KO42 were subjected to what is called “aversive conditioning”. This includes approaching, yelling at and throwing objects (rocks, coral, sticks, debris) at these males in an attempt to make them flee areas where pups haul out. Initially these interventions occurred during attacks; however, once the two males displayed a pattern of aggression, staff intervened upon sighting either male. One pup with an abscess was treated with antibiotics and two recently weaned female pups were translocated from an area frequented by aggressive males to an area closer to the scientists’ field camp to facilitate observation and protection.

Permitted Mitigation Options for Individual Male Aggression

NOAA Fisheries has three options for removing aggressive male monk seals under ESA/MMPA Permit 10137-06: 1) translocation, 2) permanent captivity, and 3) lethal removal by humane euthanasia. The permit allows for males to be removed:

"in cases where the individual seals are known or strongly suspected of causing serious injury or mortality of conspecifics as a result of single or multiple male aggression. Euthanasia would be considered in cases where the identity of male aggressors is certain; circumstantial evidence overwhelmingly indicates direct participation in such attacks; or, researchers have been able to stop the attacks and treat injured seals, but the adult male continues the aberrant behavior."

Before euthanasia can be considered, the options of translocation or moving males into captive facilities must be analyzed and justifiably discounted. When examining options for aggressive males at Kure, NOAA Fisheries determined that translocation and placement in a captive facility were not reasonable, feasible or humane.

  1. Translocation: Transporting these male seals to any location within the Hawaiian archipelago may simply put other young seals at risk wherever the aggressors are released. The only viable alternative destination for translocation is Johnston Atoll. Based on previous translocation experience, animals moved to Johnston Atoll appear not to persist there and are not re-sighted elsewhere. We believe the seals either died at Johnston Atoll for unknown reasons (such as shark attack or lack of food) or perished at sea in an attempt to navigate back to Hawaii. Thus, while translocation to Johnston Atoll avoids direct euthanasia, it still amounts to biological removal and is considered less humane if the seals suffer either shark attack or a slow, lingering death.
  2. Captivity: In consultation with NOAA Fisheries’ Office of Protected Resources in Silver Spring, Maryland, it was determined that none of the four facilities permitted to maintain Hawaiian monk seals in captivity could accommodate an adult male at this time. Because the permit process is lengthy, any other facility that might be interested could not obtain a permit in a timely manner that would allow captivity during this field season. Waiting until next field season would allow these male seals to attack and potentially kill young seals throughout the winter.
  3. Euthanasia: Based on NOAA Fisheries’ previous experience with aggressive male monk seal behavior, there is no reason to believe that this behavior will extinguish on its own in the next several years. Regrettably, at this time, the only viable option remaining is the lethal removal of male seals that meet removal criteria. MMPA/ESA permit 10137-06 specific to the lethal removal of aggressive male seals states:

    "As a last resort to remove adult males, over the five-year period of the permit up to 10 adult male seals may be humanely euthanized if they are known or strongly suspected of causing serious injury or mortality of conspecifics."

    "An experienced veterinarian or highly qualified researcher under veterinary consultation must conduct the euthanasia. After necropsy, all parts not retained from seals chemically euthanized must be collected for environmentally safe disposal."

Decision Regarding Kure Aggressive Males

In response to the high frequency and severity of male aggression related injuries and mortality at Kure Atoll in 2011, NOAA Fisheries has determined intervention is necessary. Through detailed observation and documentation of individual male seals involved in aggressive attacks on conspecifics in 2010-2011, two males (KE18 and KO42) are candidates for removal.

KE18 is clearly subject to lethal removal. He has exhibited increasing aggression over the course of two field seasons, and has inflicted several injuries, including severe injuries that have led to the disappearance and likely death of two pups. Further, despite attempts to haze him away from pups, he has continued to focus aggression on young animals. If left in place, it is near certain that KE18 would continue to harm or kill pups. NOAA Fisheries has determined that euthanasia of adult male seal KE18 is the only prudent course of action to eliminate this threat to the population.

K042 is a more equivocal case. His actions are not known to have led to a pup's death, although he did behave aggressively towards several seals which sustained and recovered from moderate wounds. Unlike KE18, K042 was not observed behaving aggressively in the previous field season (2010). This may in part be due to aversive conditioning methods applied at that time. His location and involvement in aggression elsewhere are uncertain. In summary, observations of K042 to date do not meet the threshold for lethal removal at this time. He will be monitored carefully, and his case will be reevaluated as new information accrues.

The loss of KE18 from the monk seal population at Kure Atoll is likely to be more than balanced by the associated reduction in mortality of future monk seals pups and juveniles of both sexes with a positive effect on the overall population.

Field Plan for Euthanasia

On July 30, 2011 NOAA Fisheries began a cruise on the NOAA Ship Oscar Elton Sette to retrieve their field camps. During this cruise the program intends to spend five days at Kure Atoll searching for KE18. The two islands within the atoll will be surveyed several times each day.

If KE18 is located, the best method of euthanasia given the situation at the time will be determined. Ideally, KEI8 would be captured and sedated using standard protocols. All procedures will be under the guidance of an experienced veterinarian in accordance with permit requirements. Once sedated, the seal may be euthanized using a firearm or chemicals. The use of both methods is approved as humane by the American Veterinary Medical Association.

NOAA Fisheries would prefer using a firearm for euthanasia, primarily due to human and environmental safety concerns associated with the use of chemical euthanasia. After the animal is euthanized, a necropsy would be conducted on site. If chemical euthanasia were used, all fluids would need to be captured so they don't contaminate the environment, where they would persist and potentially kill or sicken other organisms. During this time, NOAA staff would have to wear additional protective gear during the 3-5 hour necropsy. The remains would need to be transported to the ship, kept in sealed containers, and then cremated upon return to Honolulu. While every precaution would be taken, the possibility still exists that some lethal chemicals could potentially be introduced into the environment at Kure Atoll.

A firearm would be operated by trained and licensed staff and strict firearm control and access protocols will be in place aboard ship. The use of a firearm will eliminate the risk associated with use of lethal chemicals and will still allow for an onsite necropsy. Additionally, the remains would not need to be transported back to Honolulu for disposal, and can rest within the Monument.

NOAA Fisheries recognizes that the lethal removal of monk seals may seem contrary to the agency’s mission and goal of recovering the species; however this decision was made after careful evaluation of the situation and after exhausting all other available options. We believe that while every seal is precious to a species that is in crisis, NOAA needs to consider what is in the best interests of the overall population for the long term.

If you have questions or comments to convey to us, please send us an email at pirohonolulu@noaa.gov. While we may not be able to respond to every comment, we appreciate hearing from you.