Thierry M. Work1 and George H. Balazs2
|1U.S. Geological Survey, Biological Resources Division, National Wildlife Health Center, Honolulu Field Station, P.O. Box 50167, Honolulu, Hawaii 96850 USA|
|2National Marine Fisheries Service, Southwest Fisheries Science Center, Honolulu Laboratory, 2570 Dole Street, Honolulu, Hawaii 96822-2396, USA|
Since at least the mid-1980s, green turtles in the Hawaiian Islands have increasingly been found afflicted with fibropapillomatosis (FP), a disease first described in green turtles from Florida. Most studies on marine turtle mortality and morbidity have either focused on particular diseases or epizootics. Surveys to identify general causes of mortality in green turtles are relatively few. Yet, such surveys could provide valuable clues to relative impact of different causes of mortality on green turtle populations. From 1993-1996, we conducted systematic pathologic exams on 49 dead or moribund green turtles from various islands in Hawaii. FP was the most common cause of morbidity/mortality in Hawaiian green turtles followed by trauma and miscellaneous diagnoses. Internal tumors were seen in 38% of FP afflicted turtles and FP afflicted turtles were severely hypoproteinemic and anemic.
Seven of 49 turtles had to be frozen after being found dead; the remainder were moribund animals humanely euthanized with lethal injection due to poor prognosis. Prior to euthanasia, blood was procured from the heart and placed in heparin or serum separator tubes. We obtained hematocrit and estimated total solids according to standard methods.
Each turtle underwent a complete external and internal exam of all major organ systems. We recorded sex, straight carapace length, weight, and quantified and measured all tumors. Representative tissues were fixed in 10% formalin and processed routinely for histopathology. Where applicable, special stains were made to identify fungi, connective tissue, and sulfated mucopolysaccharides, respectively. Select tissues were cultured for bacteria and fungi on agar media and for viruses on green turtle embryo cell lines.
Animals were grouped into diagnostic categories according to the most significant pathologic findings. These included 1) Fibropapillomatosis for those animals with skin, eye, internal or oral tumors; 2) Trauma for animals with no tumors and gross lesions of hemorrhage and fractured shell/bones or foreign body ingestion; 3) Miscellaneous for all other diagnoses; and 4) Undetermined for those animals for which cause of death could not be discerned. Straight carapace length, hematocrit and estimated total solids of moribund and healthy turtles were compared to t-test (Á=0.05).
Fibropapillomatosis was the most common diagnosis (73%). External tumors were seen on the eyes, glottis, cloaca and skin and classified as fibropapillomas Twenty-eight percent of animals in this group had internal tumors most commonly in the lungs followed by kidney, skeletal muscle, heart, liver, spleen and bone. Based on staining and morphology, tumors in the lungs, liver, spleen and kidneys were classified as fibromas or myxofibromas. Tumors in the skeletal muscle, heart and bone were classified as fibrosarcomas of low grade malignancy. Condition of the animals ranged from emaciated to excellent.
Trauma made up 10.2% of diagnoses. Two turtles died from known forced submergence in gill nets. Two others were hit by watercraft. One turtle died from intestinal perforation accompanied by sever peritonitis secondary to fishing line ingestion.
Miscellaneous diagnoses (8.2%) included one animal with severe bacterial pneumonia, one turtle with presumptive myocarditis of unknown origin, one turtle with severe egg yolk peritonitis, and one turtle with severe vascular trematodiasis and bacteremia secondary to massive vascular trematode infection. Almost all animals in all categories had varying degrees of vascular trematode infection.
For the remainder of the turtles, cause of death could not be determined because lesions encountered were very mild or no lesions indicative of cause of death were noted.
Hematocrit and estimated total solids of stranded turtles were significantly lower (P<0.0001) than those of free-ranging healthy turtles. Straight carapace lengths between the two groups did not differ significantly (P=0.64). Thirty-four animal were immatures, 10 subadults and five adults.
FP is the most common cause of morbidity and mortality in free-ranging green turtles in Hawaii, and appears to affect mostly immature animals. Animals afflicted with FP are severely hypoproteinemic and anemic, but not all are necessarily emaciated. Some internal tumors of FP-afflicted animals appear locally invasive, particularly those within skeletal and heart muscles. Prevalence of vascular trematode infection in free-ranging green turtles is close to 100%. In some cases, infection is severe enough to cause mortality, especially in conjunction with FP. Future research needs to focus on elucidating the etiology of FP and life cycles of vascular trematodes.
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