Biomedical Management of the Most Endangered Pinniped in U.S. Waters: The Hawaiian Monk Seal (Monachus schauinslandi)
The Hawaiian monk seal (Monachus schauinslandi) is the only marine mammal located entirely within U.S. waters where it is the most endangered pinniped. Beach counts have declined sharply since 1985 and current abundance is approximately 1,300–1,400 seals. Population trends most likely will continue to decline due to high juvenile mortality and low reproductive recruitment at French Frigate Shoals, Northwestern Hawaiian Islands (NWHI), where the largest of the six main reproductive populations can be found. Conceivably, this species could be on the verge of extinction in 20 years. Since 1981, captive care and release programs have been an integral part of management efforts to conserve the species. Three methods have been used including headstart, direct translocation from one site to another, and transport to Oahu for rehabilitation, followed by release into a depleted wild monk seal subpopulation. Headstart was a technique that first was used in 1981 at Kure consisting of on-site protection of weaned pups from shark predation and adult males. Since 1984, female pups from French Frigate Shoals were rehabilitated in Oahu and then released into the NWHI after 8–10 months. To date, rehabilitation efforts have been halted by the development of an ocular condition of unknown etiology affecting 12 female pups captured during the summer of 1995. The seals have not been released because of the risk of spreading the disease to the wild population. Attempts to document health and disease in the species began following an epizootic of unknown etiology (although ciguatera poisoning has been suggested) that killed ~50 seals in Laysan, NWHI in 1979. Causes of mortality in the population have been identified based on field necropsies of dead individuals and in some cases, on histopathologic studies. The primary causes of monk seal mortality from 1981–1995, based on gross and histopathologic examination of 65 monk seals were identified as emaciation in 36 seals (35%), trauma in 19 seals (29%), infectious disease in 10 seals (15%), and undetermined mortality in 8 seals (12%). Gastrointestinal parasite burdens were abnormally high in 45 (69%) seals. Their significance also remains unknown. The Hawaiian Monk Seal Epidemiology Task has been recently developed to take a proactive approach in identifying health and disease parameters in the population. Its primary objectives are to centralize and maintain a serum/specimen bank, construct a long-term plan for epidemiologic research and implement an action plan for unusual mortality events.