Tanja S. Zabka1; Frances M.D. Gulland2; Martin
Haulena2; Elizabeth L. Buckles3; Diane Nayden3; Linda J.
On 4 July 2000, an adult female Steller sea lion,
Eumatopiasjubatus, stranded and died on Dillon beach, Sonoma County, California, and was
presented for necropsy to the Marine Mammal Center, Sausalito, California, three hours post
mortem. On gross examination the animal was emaciated (BCS 2/7) and had nasopharyngeal mites,
gastric nematodes, severe hepatic trematodiasis, segmentally severe enteritis, unilateral
hydroureter and small, fibrous nodules on gastric and uterine serosa, aortic adventia and renal
capsule. Within the right latissimus dorsi muscle was a single, well-demarcated, centrally
necrotic, pale yellow, 10.0 x 10.0 x 4.0cm mass, and within the left cranial lung lobe were two
firm, white, spherical 1.0 cm and 1.2 cm in diameter subpleural nodules.
Histologically, the unencapsulated, partially demarcated, centrally
necrotic, highly cellular muscle mass consisted of loosely arranged, pleomorphic, spindle-shaped
or stellate cells occasionally arranged in short or long streaming bundles. Uninucleated
neoplastic cells were mixed with multinucleated giant cells, and anisocytosis and anisokaryosis
was marked but mitosis few. Pulmonary masses were similar and accompanied by edema and subacute
The pleomorphism of neoplastic cells and abundance of multinucleate cells in
the muscle and pulmonary masses are highly suggestive of rhabdomyosarcoma. These neoplasms often
are markedly anaplastic and characteristic cross striations absent. Immunohistochemically,
neoplastic cells at both sites were reactive for vimentin, but negative for skeletal myosin,
smooth muscle actin, desmin, Factor VIII and pancytokeratin. Normal adjacent muscle stained
inconsistently with antibodies specific for myosin and desmin of canine muscle, which indicates
incomplete cross-reactivity with otarid skeletal muscle. Differential diagnoses for this
neoplasm include leiomyosarcoma, giant cell sarcoma of soft tissues and fibro sarcoma. Further
characterization is being pursued using electron microscopy.
Death in flee-ranging pinnipeds commonly is caused by pneumonia, heavy
parasite burdens and debilitation.2,7 In this older animal, these conditions in
conjunction with enteritis were likely contributory to mortality and the neoplasm incidental.
Over the last two decades, there has been a dramatic decline in the western U.S. Steller sea
lion population due to ill-understood causes, but hypothesized to be consistent with a long-term
environmental change or novel catastrophe.8,10 Post mortem data are rare because of
the difficulty in recovering carcasses fresh enough to yield beneficial information.
Previous reports of neoplasia in this species are limited to metastatic
pulmonary adenocarcinoma9, palpebral neoplasia, probable fibroma (Spraker, pers.
comm.), and uterine fibroleiomyoma.7 However, with the documented increasing
incidence of neoplasia in marine mammals1,2,5,6, it is important to consider and
identify predisposing and causative factors, such as infectious agents and biomagnification of
exogenous pollutants in top predators predisposing or causing systemic alterations and diseases,
such as immunocompromise and neoplasia.
As top predators ourselves, diseases manifested in marine fauna may reflect
those to anticipate in the human population and present concerns for sustainable use
alternatives of marine populations.
1. Buckles E.L., Lowenstine L.J., Garber R., Spraker T., Lipscomb
T., Haulena M, Gulland F.M.D. 1999. Current investigations into the etiology and pathogenesis of
neoplasms in California sea lions (Zalophus californianus). In: Proceedings from the
IAAAM 30 th Annual Conference, New England Aquarium, Boston, Pp 99-101.
2. Howard E.B., Britt J.O., Simpson J.G. 1983. Neoplasms in marine
mammals. In" Pathobiology of Marine Mammal Diseases, vol II. E.B. Howard (ed). CRC press,
Boca Raton, Florida, Pp 95-107.
3. Jubb K.V.F., Kennedy P.C., Palmer N. 1993. Muscles, neoplastic
diseases. In: Pathology of Domestic Animals, 4 th ed, vol I. Academic Press, Inc., New York, Pp
4. Lee J.S., Tanabe S., Umino H., Tatsukawa R., Loughlin T.R.,
Calkins D.C. 1996. Persistent organochlorines in Steller sea lion (Eumetopiasjubatus)
from the bulk of Alaska and the Bering Sea, 1976-1981. Marine Pollution Bulletin 32(7)"
5. Lipscomb T.P., Scott D.P., Garber R.L., Krafft A.E., Tsai M.M.,
Lichy J.H., Taubenberger J.K., Schulman F.Y., Gulland F.M. 2000. Common metastatic carcinoma of
California sea lions (Zalophus californianus) evidence of genital origin and association
with novel gammaherpesvirus. Vet Pathol 37(6): 609-17
6. Martineau D., De Guise S., Foumier M., Shugart L.R., Girard C.,
Lagace A., Beland P. 1994. Pathology and toxicology of beluga whales from the St. Lawrence
Estuary, Quebec, Canada. The Science of the Total Environment 154:201-115.
7. Morgan L., Hanni K., Lowenstine L. 1996. Age and pathological
findings for two Steller sea lions stranded on the northern Califomia coast. California Fish and
Game 82(2)" 81-86.
8. Pascual M.A., Adkison M.D. 1994. The decline of the Steller sea
lion in the northeast Pacific" demography, harvest or environment. Ecological Aplications
9. Sato S., Kitamura H., Mori M., Fukazawa M., Takeda M., Kadota
K. 1998. Adenocarcinoma of the lung in a Steller sea lion (Eumatopiasjubatus). J Vet Med
Sci 6(12): 1349-1351.
10. Sease J.L., Merrick R.L. 1997. Status and population trends of
Steller sea lions. In" Symposium of the 127th Annual Meeting of the American Fisheries
Society, Pinniped populations, Eastern North Pacific" Status, Trends and Issues. Stone G.,
Goebel J. and Webster S. (eds). Monterey, California.