Threats To Hawaiian Monk Seal Survival

The Hawaiian Monk Seal Research Program (HMSRP) works to identify sources of monk seal injury, emaciation, and mortality to focus research and conservation efforts aimed at mitigating these threats impeding population recovery. Current known threats include adult male aggression; climate change; food limitation; human interactions; infectious disease, parasites, and toxins; marine debris; and shark predation.

Threats to Hawaiian monk seal survival Adult Male Aggression Climate Change Food Limitation Human Interactions Infectious Disease, Parasites and Toxins Marine Debris Shark Predation
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Adult Male Aggression

Primary Area Affected: Northwestern Hawaiian Islands

Events involving single to multiple adult male Hawaiian monk seals exhibiting aggression towards adult females and immature seals has led to a significant number of severe injuries and deaths. Unfortunately, the loss of even a single female, and the loss of her lifetime reproductive potential, represents a significant setback to population recovery of this endangered species. This threat continues to be a concern, even though it tends to be episodic and geographically limited.

Recovery and Intervention Activities: Treating injured seals when appropriate, hazing of identified aggressors, translocating pups from areas where aggressive males frequent and removal of the aggressive males.

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Climate Change

Primary Area Affected: Northwestern Hawaiian Islands

Many of the remote low-lying islands of the Northwestern Hawaiian Islands are less than 2 meters (6.6 feet) above sea level. These islands and atolls support ca. 80-90% of the entire Hawaiian monk seal population, and provide critical resting, molting and pupping habitat necessary for survival. The potential loss of this habitat (from storm erosion and sea level rise) may increase seal densities on the remaining terrestrial habitat and potentially increase competition between seals.

Additionally, shifts in ecosystem productivity, either from cyclical events and/or global climate change, may impact available food resources for foraging seals.

Recovery and Intervention Activities: Continued monitoring to assist in planning mitigation strategies necessary, particularly for the Northwestern Hawaiian Islands.

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Food Limitation

Primary Area Affected: Northwestern Hawaiian Islands

Limited prey availability is the primary factor attributed to emaciation and poor survival of juvenile monk seals and the resulting decline of the Hawaiian monk seal population in the Northwestern Hawaiian Islands (NWHI). Seals in the NWHI must compete for food with a larger population of other top (apex) predators, sharks and jacks (trevally or ulua). Additionally, shifts in ecosystem productivity, either from cyclical events and/or global climate change, may be contributing to food limitation.

Recovery and Intervention Activities: Translocation of seals to other islands or atolls with improved foraging conditions and captive rehabilitation of malnourished animals.

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Human Interactions

Primary Area Affected: Main Hawaiian Islands

Human actions and activities are diverse and can adversely impact the survival of monk seals. Seals haul out on land for important biological needs: to rest, molt, give birth, and care for their pup. Disturbing seals, either unintentionally or deliberately, can have negative consequences, as the seal may use important energy reserves to move away, or in the case of a mother seal, to defend her pup.

Intentional feeding and direct interactions, such as swimming and encouraging seals, particularly juvenile seals, may teach an animal to seek out humans, deprive young animals of learning important survival skills and can lead to aggressive behaviors as the seal becomes older and bolder. Seals may become sick, injured or unintentionally or intentionally killed, by seeking out humans, approaching boats (boat strikes), ingesting unnatural or indigestible food items or becoming hooked/entangled in fishing gear.

Recovery and Intervention Activities: Education and outreach to prevent/ minimize human-seal interactions. Applying behavioral conditioning, translocating or bringing into captivity seals that pose a human safety risk. Dehooking seals and encouraging fishermen to use barbless hooks and to avoid fishing when a seal is in the area.

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Infectious Disease, Parasites and Toxins

Primary Area Affected: Both Northwestern and main Hawaiian Islands

Some diseases pose a risk to Hawaiian monk seals include distemper viruses, West Nile Virus, Leptospira spp., and Toxoplasma gondii. Since seals travel between the main and Northwestern Hawaiian Islands (NWHI), an infection could easily spread throughout the entire population with disastrous consequences.

The prevalence of gastrointestinal parasitic infections throughout the monk seal population is significant and the effects on monk seal morbidity and mortality are not fully known. The high rate of infection, concurrent with prey limitation, may be a significant factor affecting seal survival in the NWHI.

Monk seals are also at risk to human originated and naturally occurring toxins. The ingestion of contaminated prey could result in bioaccumulation of the toxins in the tissues and have deleterious health consequences.

Recovery and Intervention Activities: Monitoring health (including disease, parasitic infections and toxin screening), providing appropriate medical treatment (including deworming), and continuing vaccination research and response planning.

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Marine Debris

Primary Area Affected: Northwestern Hawaiian Islands

Hawaiian monk seals have one of the highest entanglement rates of any pinniped (seal or seal lion) species. Pups are proportionally entangled more frequently than older animals. Monk seals have been entangled in many types of debris, including nets, lines, straps, and rings (including hagfish or eel traps), and other miscellaneous items (e.g., bucket rims, bicycle tires, rubber hoses). Intensive efforts are undertaken by NOAA and other agencies to remove debris from beaches and nearshore waters; however, the accumulation rates in the Northwestern Hawaiian Islands appear to remain constant.

Recovery and Intervention Activities: Disentangling seals and removal of marine debris from beaches and marine habitat.

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Shark Predation

Primary Area Affected: Northwestern Hawaiian Islands, specifically French Frigate Shoals

Predation by Galapagos sharks is the major cause of injury and mortality on nursing and newly weaned pups at French Frigate Shoals. This unique and relatively recent source of mortality appears to be a result of atypical behavior of a limited number of Galapagos sharks that prey on pups in the nearshore waters, often just feet from shore.

Recovery and Intervention Activities: Translocation of newly weaned pups to areas with low shark predation risk and limited lethal removal of Galapagos sharks from nearshore pupping habitat.

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