Hawaiian Monk Seal Population at a Glance

Long-term trends in Hawaiian monk seal beach counts (an index of the total population) for all Northwestern Hawaiian Islands 
        combined from 1958-2016.  Main Hawaiian Island monk seal counts are not included as there is not comparable data.
Long-term trends in Hawaiian monk seal beach counts (an index of the total population) for all Northwestern Hawaiian Islands combined from 1958-2016. Main Hawaiian Island monk seal counts are not included as there is not comparable data.
Range-wide estimates of Hawaiian monk seal abundance from 2013 to 2016. The median estimates and 95% confidence limits (in 
        parentheses) are provided
Range-wide estimates of Hawaiian monk seal abundance from 2013 to 2016. The median estimates and 95% confidence limits (in parentheses) are provided.

The Hawaiian monk seal, one of the rarest pinniped (seal and sea lion) species on Earth, was listed as Endangered under the US Endangered Species Act (ESA) in 1976.

The majority of the population (ca. 80%) is distributed throughout the 8 remote islands and atolls of the Northwestern Hawaiian Islands (NWHI) within the Papahānaumokuākea Marine National Monument (PMNM), (Nihoa Island, Mokumanamana (Necker Island), French Frigate Shoals, Laysan Island, Lisianski Island, Pearl and Hermes Reef, Midway Atoll, and Kure Atoll). Each site contains a subpopulation of seals exposed to varying ecological conditions.

A prolonged decline in abundance of Hawaiian monk seals in the NWHI occurred since systematic studies of the species began in the late 1950s. While the individual subpopulations have varied out of synch at times (some declining, others stable or increasing), their total abundance dwindled for several decades. However, recent trends suggest the number of seals in the NWHI is stabilizing and possibly even increasing, in part due to NOAA Fisheries recovery efforts. Generally, better survival of young seals in recent years seems to be driving the improved abundance trends.

The smaller main Hawaiian Islands (MHI) monk seal population appears to have been growing since at least the 1990s despite the large human population in the islands. Until the recent improvements seen in the NWHI, MHI monk seals have had much higher average survival rates. There are signs that environmental conditions, especially food availability per seal, have been more favorable in the MHI. For example, MHI seals grow faster, reach reproductive maturity sooner and give birth more frequently on average compared to their counterparts in the NWHI. Seals in the NWHI and MHI face different threats, which necessitate specific conservation and recovery strategies for each area.

To learn more about the 2 main monk seal subpopulations, click the following links:

Hawaiian Monk Seal Population Size by Island

The range-wide total population estimate for 2016 was 1,427 seals. There has been an increasing growth rate of 3% per year from 2013-2016. The accuracy of estimates varies a great deal depending upon how much research effort is able to be conducted at each site. For example, at most of the NWHI sites where field camps are present for several months, the estimates are usually accurate to within a few tens of seals. In contrast, at Necker, Nihoa and Niʻihau Islands only a few counts can be made each year, resulting in far more uncertain estimates. A rough breakdown of the population sizes per sites are:

Population Size Range
(#seals per site)
Sites
50 to 100 Necker, Midway and Kure
100 to 200 Nihoa, French Frigate Shoals, Lisianski Island and Pearl and Hermes Reef
200 to 300 Laysan Island and the Main Hawaiian Islands
Northwest Hawaiian Islands overview map
Click image above to view larger map.

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