Abstract
The western population of Steller sea lions (Eumetopias jubatus) is classified as endangered on the International Union for the Conservation of Nature Red List of Threatened Species.1 Pathology from free-ranging Steller sea lion (SSL) populations has been documented; however, these data from SSLs in aquariums are currently lacking.2-6 The objective of this study was to identify common and significant causes of morbidity and mortality in adult SSLs under human care to optimize clinical management.
A retrospective review of gross and histopathological reports of SSLs under human care in North America (n=20) from 1979–2021 was performed. Individuals were included if they had reached sexual maturity and were either born under managed care or had been housed in a facility for at least five years. Eleven SSLs were found deceased, eight were euthanized, and one case was not specified. Associations between age, sex, or birth origin (under human care versus the wild) with cause of death (COD) and organ pathology were explored using Chi Square or Fishers Exact Tests (α=0.05). The most common COD was neoplasia (n=10), which was significantly associated with aged animals (Ꭓ(16)=27.371; p=0.038). Less frequent COD included sepsis (confirmed n=2, suspected n=2), clostridial enteritis (n=1), multisystemic inflammation (n=1), sarcocystis (n=1), cardiomyopathy (n=1), suspected adverse reaction to sedation (n=1), and unknown (n=1). COD were not statistically different amongst animals born in human care versus the wild, nor between sexes. Documented types of neoplasia included multicentric lymphoma, sarcomatous malignant mesothelioma, unspecified sarcoma, sarcomatoid carcinoma, neuroendocrine carcinoma, thyroid carcinoma, pancreatic adenocarcinoma, adrenocortical carcinoma, pheochromocytoma, thyroid adenoma, uterine leiomyoma, and meningioma. Age was also significantly associated with development of endocrine organ pathology (Ꭓ(2)=9.107; p=0.011). Cardiovascular and ocular disease approached significance in aged animals as well (Ꭓ(2)=5.683; p=0.058). Body systems commonly associated with primary pathologic changes on final diagnosis were hepatobiliary (13/20, 65%), gastrointestinal (12/20, 60%), endocrine (12/20, 60%), lymphoid (12/20, 60%), and urinary (11/20, 55%). Moderately affected systems were reproductive (9/20, 45%), respiratory (7/20, 35%), cardiovascular (7/20, 35%), musculoskeletal (7/20, 35%), and ocular (7/20, 35%). Rarely affected organs included nervous system (4/20, 20%) and integument (4/20, 20%).
Causes of mortality in SSLs in aquariums differed substantially from free-ranging populations, as anthropogenic-induced pathology, predation, parasitism, or malnutrition were not documented in the current study.2-5 This is the first report highlighting the high prevalence of neoplasia in SSLs, with malignancies found in three cases not associated with COD, frequent metastasis (10/13, 77%), and several animals (6/13, 46%) with multiple types of primary neoplasia concurrently. Multiple primary malignancies in non-domestic species have infrequently been reported.7,8 Additionally, documentation of neoplasia in marine mammal species aside from California sea lions and belugas from the St. Lawrence Estuary are typically limited to single case reports.8-10 Only three types of malignancies had been reported in SSLs prior to this study.6,10 These data expand the current understanding of disease in SSLs, highlight this species’ predisposition to neoplasia, and underscore the need for heightened screening in aged animals, which may ultimately serve to elevate the care of SSLs under human care.
Acknowledgements
The authors wish to thank Gayle Sirpenski for locating SSL records in Mystic Aquarium archived files and databases.
*Presenting author
+Student presenter
Literature Cited
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