Hawaiian Monk Seal Population at a Glance

Trend in abundance at 6 main NWHI subpopulations indicates an average 3.4% decline per year from 2002-2011. Note: Graph does not include MHI, Mokumanamana (Necker), or Nihoa where reliable time series data of total abundance are not available.
Trend in abundance at 6 main NWHI subpopulations indicates an average 3.4% decline per year from 2002-2011. Note: Graph does not include MHI, Mokumanamana (Necker), or Nihoa where reliable time series data of total abundance are not available.
Projection of possible NWHI and MHI population sizes based on current rates of growth. By 2024, the NWHI population may decline to a level where seal numbers would equal the MHI population size.
Projection of possible NWHI and MHI population sizes based on current rates of growth. By 2024, the NWHI population may decline to a level where seal numbers would equal the MHI population size.

The Hawaiian monk seal, one of the rarest pinniped species on Earth, was listed as Endangered under the US Endangered Species Act (ESA) in 1976. The NWHI population has declined 3.4% annually over the past decade. In 2011, the total minimum abundance of Hawaiian monk seals was estimated at 1,100 animals throughout the Hawaiian Archipelago.

The majority of the population (ca. 90%) is distributed throughout the remote islands and atolls of the Northwestern Hawaiian Islands (NWHI) within the Papahānaumokuākea Marine National Monument (PMNM). Each island contains a semi-isolated subpopulation of seals that face unique ecological pressures and conditions. While fishing pressure and human activity have been minimized within this vast marine environment, the population as a whole continues to decline.

Conversely, in 2011 a minimum of 150 seals resided in the main Hawaiian Islands (MHI) population that has slowly increased over the past ten years. Despite high levels of human activity around the MHI, monk seals appear to be in good physical condition and survival rates of pups are much higher than those in the NWHI.

The demographics of the monk seal populations in the NWHI and MHI are strikingly different. Seals residing in the NWHI have decreased survival rates, reproductive success, and overall body condition compared to those of the MHI. A variety of physical and environmental factors can account for these differences, and necessitate specific conservation and recovery strategies for each area.

Estimated Hawaiian Monk Seal Population Size by Island

Northwest Hawaiian Islands overview map Kure Atoll population Midway Atoll population Pearl and Hermes Reef population Lisianski Island population Laysan Island population French Frigate Shoals population Mokumanamana Island population Nihoa Island population Main Hawaiian Islands population
Click image above to view larger map.
Northwest Hawaiian Islands overview map
Location Estimated 2011 Population Size1
Kure Atoll 110
Midway Atoll 50
Pearl and Hermes Atoll 181
Lisianski Island 152
Laysan Island 226
French Frigate Shoals 190
Main Hawaiian Islands >150
1 These population estimates include the number of uniquely identified seals observed at all islands, but are considered a minimum size as not all seals may have been present during the observation period or could be identified as a unique animal. Seals seen at more than one island are counted only at one location. Additionally, there are gaps in information from areas that are more remote or have limited accessibility including Nihoa and Mokumanamana (Necker) in the Northwestern Hawaiian Islands and Ka'ula, Ni'ihau, Lehua, and Kaho'olawe in the main Hawaiian Islands.
Location Estimated 2011 Population Size1
Kure Atoll 110
Midway Atoll 50
Pearl and Hermes Atoll 181
Lisianski Island 152
Laysan Island 226
French Frigate Shoals 190
Main Hawaiian Islands >150
1 These population estimates include the number of uniquely identified seals observed at all islands, but are considered a minimum size as not all seals may have been present during the observation period or could be identified as a unique animal. Seals seen at more than one island are counted only at one location. Additionally, there are gaps in information from areas that are more remote or have limited accessibility including Nihoa and Mokumanamana (Necker) in the Northwestern Hawaiian Islands and Ka'ula, Ni'ihau, Lehua, and Kaho'olawe in the main Hawaiian Islands.

Monk Seal Range and Movements

In the Northwestern Hawaiian Islands, there are 8 discrete monk seal subpopulations from Nihoa Island to Kure Atoll (excluding Gardner Pinnacles and Maro Reef), a distance of 2000 km (1,243 miles). A small number of seals are seen on each of the 8 main Hawaiian Islands, and births have been documented on every island except for Lanai. A few monk seals have been sighted at Johnston Atoll and a birth was documented in 1969. Hawaiian monk seals tend to remain at their natal (birth) island for life; however, some move between or among major population centers. A comprehensive review and analysis of monk seal movements is currently being conducted.