Abstract

Of the seven species of marine turtles, all are listed as threatened or endangered. The two species of sea turtles that nest in Hawaii are the hawksbill and the green, the latter being much more numerous. Since turtles were listed as endangered in 1973, populations of nesting adult green turtles at the main breeding site in French Frigate shoals have been increasing by 5 percent per year. However, since the early 1950s, prevalence of the tumor disease, fibropapillomatosis (FP), has increased in Hawaiian turtles. This disease is of concern because it affects mainly immature animals with prevalence ranging from 40-60 percent. Available evidence indicates that FP, which causes unsightly external and internal tumors, has a high fatality rate and that it is the most important cause of morbidity and mortality in wild near-shore green turtles. Current data indicate the disease is transmissible through cell-free filtrates and implicate a herpesvirus as strongly associated with presence of tumors. However, Koch's postulates have not been fulfilled. A system to score severity of FP in wild green turtles was developed in Hawaii and has been used successfully to show that turtles become immunosuppressed and bacteremic with increasing severity of disease. In addition to being afflicted with FP, stranded turtles have a 100 percent prevalence of infection with vascular trematodes that can cause significant pathology. Finally, it is likely that environmental co-factors play a role in disease based on distribution of affected animals. Current efforts are underway to isolate the herpes virus associated with tumors and to develop diagnostic tests to assess exposure of wild turtles to this virus.

Investigations into causes of mortality in wildlife would be incomplete without examining all life history stages. As such, for the past 4 years, we have been conducting systematic exams of sea turtles caught in the North Pacific pelagic longline fisheries. In most cases, turtles from these fisheries have died from forced submergence; however, the two specimens of leatherback turtles examined had internal inflammatory lesions of unknown cause. Because the leatherback turtle is in critical danger of extinction in the Eastern Pacific, efforts have been initiated to investigate causes of mortality in this species. Biologists in the Western and Eastern Pacific were trained in necropsy techniques and sample collection, and they received a necropsy manual. To date, difficulty in locating suitable carcasses for examination and paucity of animals on nesting beaches has hampered efforts to assess health in this species.