Hawaiian Monk Seal Population - Main Hawaiian Islands

MHI monk seal sleeping

MHI monk seal near crowded beach. Photo by D.B. Dunlap.
Photo by D.B. Dunlap.

The main Hawaiian Islands (MHI), the geologically youngest and largest islands at the southeastern end of the archipelago, include the 8 main islands of Hawaiʻi, Kahoʻolawe, Maui, Lanaʻi, Molokaʻi, Oʻahu, Kauaʻi and Niʻihau; small uninhabited volcanic islets including Kaula Rock, Lehua and Molokini Crater; and numerous smaller islets offshore the main islands.

Genetic evidence suggests that the Mediterranean and New World monk seals (Hawaiian and Caribbean seals) diverged 6.30 million years ago and the Hawaiian monk seals diverged from the Caribbean monk seal (their closet relative) 3.67 million years ago around the time of the closure of the Panama Canal. It is unknown when the ancestral pinnipeds reached the Hawaiian Archipelago. As a large insular (island-based) carnivore, monk seals may never have existed in large numbers, and records from the 19th century indicate intense commercial and sustenance hunting which led to the near extinction of the species throughout the Hawaiian Archipelago.

There are documented sightings of monk seals in the MHI going back to the 1800's and archeological remains of monk seals found on Hawaiʻi Island dating to 1400-1700 AD. Between 1928 and 1956 there were only seven monk seal sightings within the MHI. Seals only became common after 1970 on Niʻihau, and it is suggested that individuals may have spread from there to other parts of the MHI. In addition to this natural re-colonization of the MHI, 21 adult male seals were translocated from the Northwestern Hawaiian Islands (NWHI) in 1994 to alleviate high levels of male seal aggression resulting in mortality of adult female and immature seals due a male biased sex-ratio at Laysan Island. However, these males cannot account for the natural, unassisted population growth that is now underway. The increasing MHI population is a result of high reproductive success of seals already here, and not by seals moving here from the NWHI.

The MHI subpopulation represents a small portion of the total population and is continuing to expand, in contrast to the declining subpopulation in the NWHI. Thus the MHI monk seal population has assumed additional importance from a management and species recovery perspective. For the species as a whole, the increasing utilization of the MHI allows for greater terrestrial and foraging habitat availability. Today, the MHI provide over 2,300 km (1,429 miles) of shoreline habitat, which is nearly 30% larger than the NWHI.

In comparison to the monk seals in the NWHI, MHI animals are generally in excellent physical condition, indicating abundant food resources in the MHI. This increased prey availability is likely a byproduct of limited competition from other seals due to current low MHI population numbers. In addition, as a result of heavy recreational and commercial fishing pressure on jacks (trevally or ulua) and sharks around the MHI, competition for food with these other top predators is lessened. The excellent condition of the MHI seals is a favorable indicator for continued population growth in the MHI.

Despite the population level benefits of an expanding MHI subpopulation, there are unique concerns and management challenges associated with growth in the region. Due to increased exposure to humans and domesticated and wild mammals, the possibility of disease exposure and transmission throughout the population may be elevated. Monk seals residing near large human population centers are also exposed to toxins from sewage discharge, urban and agricultural run-off and oil spills polluting the nearshore marine environment and contaminating prey they consume. The number of fishery-related injuries and mortalities (from hooking or entanglement) has been increasing in recent years and additional vessel traffic around the MHI increases the potential for collision. Finally, with an expanding Hawaiian monk seal subpopulation in the MHI there have been an ever increasing number of human-seal interactions, where a small number of habituated seals became a human safety risk or have incurred injuries as a result of interacting with people. Other potentially harmful interactions include human and dog disturbances to resting and molting seals or mother-pup pairs on beaches and intentional killing. Addressing these increasing threats will require proactive and innovative measures along with public support to continue the positive growth of this subpopulation.

Additional Information

Monk Seals in Native Hawaiian Culture

Honua Consulting [honuaconsulting]
2010, December 1. A Priviledge to See - Hawaiian Monk Seals from an Island Perspective [Video file]. Retrieved from https://www.youtube.com/watch?v=jJsuqUAU_to
Kittinger JN, Bambico TM, Watson TK, Glazier EW
2011. Historical and Contemporary Significance of the Endangered Hawaiian Monk Seal in Native Hawaiian Culture. A report prepared for the NOAA Pacific Islands Regional Office. Impact Assessment, Inc., Honolulu
Nordtvedt Reeve LL, Reeve RB, Cleghorn PL
2013. The Hawaiian Monk Seal in Traditional Hawaiian Culture. A report prepared for the NOAA Pacific Islands Regional Office. Pacific Legacy, Inc., Honolulu

Further reading

Baker JD, Harting AL, Wurth TA, Johanos TC
2010. Dramatic shifts in Hawaiian monk seal distribution predicted from divergent regional trends. Marine Mammal Science. DOI: 10.1111/j.1748-7692.2010.00395.x
Baker JD, Johanos TC
2004. Abundance of the Hawaiian monk seal in the main Hawaiian Islands. Biological Conservation 116: 103-110. DOI: 10.1016/S0006-3207(03)00181-2
Baker JD, Johanos TC, Wurth TA, Littnan CL
2013. Body growth in Hawaiian monk seals. Marine Mammal Science. DOI: 10.1111/mms.12035
Brown E, Hughes G, Watanuki R, Johanos T, Wurth T
2011. The emergence of an important Hawaiian monk seal pupping area at Kalaupapa, Molokaiʻi in the main Hawaiian Islands. Aquatic Mammals 37(3): 319-325. DOI: 10.1578/AM.37.3.2011.319
Scheel D-M, Slater G, Kolokotronis S-O, Potter C, Rotstein D, Tsangaras K, Greenwood A, Helgen KM
2014. Biogeography and taxonomy of extinct and endangered monk seals illuminated by ancient DNA and skull morphology. ZooKeys 409 (2014): 1-33. DOI: 10.3897/zookeys.409.6244