Abstract
Most of the world’s sea otters reside in Alaska; however, there has never been an assessment of long-term mortality patterns for this keystone predator. Prior studies examining the health and disease of northern sea otters in Alaska have been limited in their timeline and scope with most examining the effects of the 1989 Exxon Valdez oil spill in Prince William Sound and found that environmental disasters can have long-term impacts on survival rates and mortality.1,2 Other studies have compared Northern sea otters in Alaska to southern sea otters in California showing low exposure to most potential marine and terrestrial pathogens but 40% exposure to PDV.3,4
We examined data collected from 780 northern sea otter (Enhydra lutris kenyoni) carcasses recovered in Alaska from 2002–2012 to evaluate the causes of mortality and risk factors associated with death. A subset of fresh non-frozen carcasses (n=144, 18%) were included in a detailed mortality analysis. From this analysis, 44% of these freshly dead otters were determined to have died from infectious endocarditis, meningoencephalitis, and/or septicemia due to systemic streptococcosis (“Strep syndrome”).5 Streptococcus lutetiensis, a member of the Streptococcus bovis/equinus (SB/E) group was most commonly isolated, although other members of the SB/E group were identified. There were fewer cases where S. phocae and other streptococci were isolated. A regression analysis revealed age and location risk factors for Strep syndrome. Subadults were the highest risk age group, and otters recovered from the Kachemak Bay region were 3.6 times (95% CI: 2.2–5.9) more likely to die from Strep syndrome than otters recovered elsewhere. Diagnosis of this Strep syndrome has not been reported in sea otters outside of Alaska or other marine mammals in Alaska. Other causes of death for the fresh otters included neurologic disease (10%), trauma (8%), nutritional causes and cardiovascular diseases (7%), gastrointestinal disease/parasites (6%), undetermined (5%), and septicemia and neoplasia (3%). All other causes of death (oiling, hepatobiliary disease, fungal, marine biotoxins, pulmonary disease) were at or below 1%. Twenty percent of tested fresh animals were positive for phocine distemper virus (PDV) by polymerase chain reaction (PCR, 11/55) and 18% seropositive for PDV (7/38). Paramyxovirus-like particles were demonstrated by electron microscopy within inclusion bodies from one animal. Related studies suggest PDV may be emerging in the Pacific correlated to changes in sea ice cover6 and our study provides the first pathologic data. Low concentrations of the harmful algal bloom toxins domoic acid and saxitoxin were also detected in 26% and 22% of fresh animals, respectively as has been reported previously.7 Protozoal disease was very rare. These patterns of disease differ from sea otters in other regions such as Washington and Oregon8 and California9 and possible reasons and significance are discussed.
Acknowledgements
We appreciate the many members of the volunteer Alaska marine mammal stranding network as well as interns and biologists that assisted us on the beaches and in the laboratory, they are too numerous to list. Special thanks go to all the staff at the Alaska SeaLife Center. We are indebted to veterinarians Carrie Goertz, Joanne Hill, and Marc Kramer, for their help with multiple necropsies and to veterinary pathologists Jennifer Chilton, David Rotstein, and Melissa Miller for their help with histology and interpretation. The WARRN-west laboratory with Dr. Kathi Lefebvre and Maryjean Willis provided DA and SXT analysis and Dr. Patricia Conrad and UCDavis Protozoal laboratory provided the analyses for Toxoplasma, Sarcocystis and Neospora. Carcasses and samples were collected under MMPA permit No. MA041309-5 issued to VAG in the U.S. Fish and Wildlife’s Marine Mammals Management office. Funding sources include the Oiled Wildlife Care Network and the Minnesota Zoo Conservation Fund and the U.S. Fish and Wildlife Service. The findings and conclusions in this article are those of the authors(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service.
*Presenting author
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