The Hawaiian monk seal (Monachus schauinslandi) is the only endangered marine mammal occurring entirely within U.S. waters. Its current population is estimated at 1,300 to 1,400 seals, a decrease of 60 percent since the 1950s. Counts declined about 5 percent per year from 1985 to 1993 and then remained relatively stable through 2002, although beach count indices indicate that numbers have declined during the last two years. Population trends are influenced by highly variable dynamics in the six main reproductive subpopulations in the Northwestern Hawaiian Islands (NWHI). Overall pup production has decreased in recent years, and juvenile survival is also decreasing in varying degrees in several subpopulations.
Monk seals occur throughout the Hawaiian archipelago, and although most monk seals occur in the NWHI, a small but increasing number of seals haulout and pup in the main Hawaiian Islands. Past and present known sources of mortality include hunting, disturbance at beach and nearshore habitats, entanglement in marine debris, shark predation, adult male monk seal aggression resulting in mortality of adult females and immature seals of both sexes, disease, and prey resource availability. The role of infectious disease, parasites, and toxins (anthropogenic and naturally occurring biotoxins) in Hawaiian monk seal population decline is an ongoing investigation.
The Marine Mammal Research Program, Honolulu Laboratory, Southwest Science Center of the National Marine Fisheries Service has actively investigated Hawaiian monk seal health and disease for more than three decades. This investigation has included surveillance and analysis, primarily in the NWHI by means of gross necropsy and histopathology, parasitology, hematology, serology, morphometrics, microbiology, epidemiology, scat and spew analysis, population abundance/survival assessment, and reproductive rates. In the fall of 2003 we anticipate that additional focused studies will be conducted in the growing main Hawaiian Islands subpopulation.