Parasites in Steller Sea Lions (Eumetopias jubatus) in Alaska
IAAAM Archive
Kathy A. Burek1; Kimberlee B. Beckmen2; Tom Gelatt3; Michelle Moore4
1Alaska Veterinary Pathology Services, Eagle River, AK, USA; 2Alaska Department of Fish and Game, Division of Wildlife Conservation, Fairbanks, AK, USA; 3Alaska Department of Fish and Game, Division of Wildlife Conservation, Marine Mammals Section, Anchorage, AK, USA; 4NOAA, National Marine Fisheries Society, Alaska Fisheries Science Center, Resource Assessment and Conservation Engineering Division, Seattle, WA, USA


There are two genetically distinct populations of Steller sea lions (Eumetopias jubatus) in Alaska, the eastern and western stocks, that are listed under the Endangered Species Act as threatened and endangered, respectively.1 As a part of multidisciplinary studies on free-ranging, live-captured and released pups and juveniles, we undertook clinical evaluations for parasites. Our objectives were to describe external and internal parasites of Steller sea lions in Alaska by collecting the external parasites and examining eggs and larvae shed in feces, and to compare parasite prevalence geographically and by age. Parasite burdens can then be correlated to a series of health parameters.

Physical examinations were performed on and blood collected from all animals. Lice, mites and any shed nematodes were preserved in ethanol/glycerol; cestodes, in AFA. Beginning in January 2000, routine fecal flotations using Fecasol® and fecalyzers were performed. Starting in August 2001, a modified Baerman's sedimentation was used on samples of higher volumes. On a small number of samples, both analyses were performed. The types of eggs and larvae were identified to group based on a key developed by Dr. K. Beckmen and references to parasitology manuals. Loads were roughly estimated on a four-point scale from 0-3. Endotracheal tube materials were examined by direct smears, sedimentation, and/or cytology.

Of 371 animals, lice were noted in 32 (nine percent). These have been identified as Antarctophthirus microchir. Nasal mites were noted when they were active on the external nares in four cases and were identified as Orthohalarachne attenuata. These are consistent with other published reports, though at relatively low rates.2,3

Flotations were performed on a total of 98 animals, 46 from the western stock and 52 from the eastern stock ranging in age from two to 26 months old. In comparing fecal flotations and sedimentations in 14 animals, sedimentation was found to be more sensitive than the flotations and were not directly comparable. Sedimentations were performed on 126 individuals, 30 from the eastern Aleutians, 48 from Prince William Sound (PWS) (both western stock) and 48 from southeast Alaska (SE) (eastern stock), ranging in age from two to 35 months. No strong trends were noted by region. Of particular interest because of potential for pathogenicity were the hookworms, lungworm, and acanthocephalans. Hookworm eggs were not seen in animals older than five months, with only one five-month old positive at a low level. In two- and three-month-old animals, 69 percent were positive for hookworm eggs by sedimentation. Lungworm larvae are generally seen in animals starting around 11 to 12 months of age and then become very common with an average prevalence of 35 percent. The youngest animal shedding larvae was one five-month-old animal from PWS, and the next youngest was one animal of nine months, also from the western stock.

Tracheal mucus examinations were performed on 65 animals. Nineteen (29 percent) of these were positive for lung mites, seven from PWS and 12 from SE. These mites have been identified as Orthohalarachne diminuata, consistent with published reports.2,3 These positive animals ranged in age from 11 to 29 months old. It seems that the mites are associated with excessive, red-tinged or mucopurulent material in the endotracheal tubes suggesting that these parasites may be causing minor bleeding and inflammation. Four were positive for lungworm larvae of a Filaroides sp. type, and three of these were also positive by fecal sedimentation. Two of these animals were from PWS, two were from SE and were 17 and 23 months old.

Five pups found dead on rookeries in southeast Alaska were opportunistically necropsied and the entire gastrointestinal tracts were submitted to AK Fisheries Science Center. Adult hookworms were collected from five animals with a parasite burden ranging from 18-191 with an average of 100/animal. These have been identified as an Uncinaria species. Hookworms in particular are poorly described and understood in Steller sea lions. Parasites have also been collected from an adult male Steller sea lion.

Reports on parasites in Steller sea lions are rare and are mostly from necropsy materials.2,3 In this study, we described eggs shed from live animals, as well as collected and identified adult parasites from necropsy materials. In the future, we will continue expanding the sample sizes in order to continue to describe patterns over age and region. Such patterns may give us information on feeding patterns, stock differences and possibly different responses to the different parasites. We also plan to determine whether there are clinical effects of these parasites by correlating findings in fecal examinations with hematology data, body condition, and morphometrics. Of particular interest are the hookworms, the lungworms, lung mites and acanthocephalans since, they have been shown to cause disease in other species of marine mammals.


The authors would like to thank Lorrie Rea and the Alaska Department of Fish and Game capture crews for making collection of these samples possible. These samples were collected under the Alaska Department of Fish and Game National Marine Fisheries Service (NMFS) Scientific Research Permit Number 358-1564-00.


1.  Bickham JW, JC Patton, TR Loughlin. 1996. High variability for control-region sequences in a marine mammal: implications for conservation and biogeography of Steller sea lions (Eumetopias jubatus). Journal of Mammalogy 77:95-108.

2.  Dailey MD, BL Hill. 1971. A survey of metazoan parasites infecting the California (Zalophus californianus) and Steller (Eumetopias jubatus) sea lion. Bulletin of the Southern California Academy of Sciences 69: 126-132.

3.  Shults LM. 1986. Helminth parasites of the Steller sea lion, Eumetopias jubatus, in Alaska. Proceedings of the Helminthological Society of Washington 53(2):194-197.

Speaker Information
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Kathy A. Burek, DVM, MS, DACVP
Alaska Veterinary Pathology Services
Eagle River, AK, USA

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