Population Assessment Shows Continuing Decline in Hawaiian Monk Seal

Operating from temporary field camps at Lisianski Island (pictured above) and other locales in the Northwestern Hawaiian Islands, PIFSC scientists monitor the abundance of the endangered Hawaiian monk seal. Data collected during the annual surveys indicate that the species is declining at about 4% per year across the Hawaiian Archipelago.

Staff of the PIFSC Protected Species Division (PSD) recently summarized monk seal population data collected during the 2008 field camps in the Northwestern Hawaiian Islands (NWHI) while continuing to collect data and respond to events in the main Hawaiian Islands (MHI).

In 2008, survey data from the NWHI show a continued decline of the monk seal population in the NWHI. The best estimate of total monk seal abundance at the six main subpopulation locations in 2008 was 914 seals, down 21 from the 2007 estimate of 935. The abundance trend at these sites, based upon a log-linear regression since 1998, is -4.2% per year.

The total number of pups born at all 6 sites in 2008 was 138, down 13 from 2007. This reduction was mostly accounted for by 12 fewer births at Laysan Island (28 in 2008 versus 40 in 2007). Births at the remaining sites numbered ± 3 compared to 2007. Survival of pups born in 2007 was poor (<0.50) at all sites except Laysan Island and Lisianski Island, continuing the pattern observed throughout the 6 main NWHI subpopulations in recent years. It may be that some yearling seals were alive but not seen due to reduced survey effort in 2008, especially at Pearl and Hermes Atoll and possibly Midway Island. The modestly higher survival rates observed at Laysan and Lisianski this year were likely inflated due to inclusion of yearlings sighted during early surveys (in March) that were not seen subsequently.

Though the situation remained bleak for the six main subpopulations in the NWHI, other areas of monk seal habitat may have growing, albeit small, populations. Several counts were conducted at Nihoa Island and Necker Island in 2008, associated in part with a pup translocation study. Mean beach counts at both sites were higher in 2008 than in 2007. Notably, 49 seals (including 11 pups) were counted on land on a single day at Nihoa. While field effort at Nihoa and Necker Islands has historically been very sparse (typically 0-2 censuses per year), the 11 pups seen at Nihoa is higher than typical. That fact, coupled with an increasing trend in counts of seals on the beach, suggests the Nihoa population may be rising.

In the MHI, aerial survey counts are highest at the island of Ni´ihau. Excluding Ni´ihau due to lack of complete information, 102 seals were individually identified in the MHI in 2008, including 18 pups born on 5 islands (Kauai, Oahu, Molokai, Kaho´olawe, and the island of Hawaii). These counts represent the highest numbers of identified seals and pups documented in the MHI to date.

For more information contact: Charles Littnan