Infectious Disease and the Decline of Steller Sea Lions (Eumetopias Jubatus) in Alaska, Usa: Insights From Serologic Data

Abstract

Serologic data were examined to determine whether infectious disease may have played a role in the decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and Aleutian Islands, USA. Available published data, unpublished data, and recent collections (1997-2000) were compared and reviewed. Data were stratified by geography to compare the declining western Alaskan population in the Aleutian Islands through eastern Prince William Sound to the increasing population in southeastern Alaska. Prevalences of antibodies from the 1970s to the early 1990s were noted for Leptospira interrogans, Chlamydophila psittaci, Brucella spp., phocid herpesvirus-1, and calciviruses. Serum samples collected from 1997-2000 were tested for antibodies to these agents as well as to marine mammal morbilliviruses, canine parvovirus, and canine adenovirus-1 and -2. Conclusions could not be drawn about changes in antibody prevalence to these agents during the decline of Steller sea lions, however, because data were incomplete or not comparable as a result of inconsistencies in testing techniques. Despite these shortcomings, results provided no convincing evidence of significant exposure of Steller sea lions to morbilliviruses, Brucella spp., canine parvovirus, or L. interrogans. Steller sea lions have been exposed to phocid herpesviruses, caliciviruses, canine adenovirus, and C. psittaci or to cross-reactive organisms in regions of both increasing and decreasing sea lion abundance. Based on similar antibody prevalence estimates from the increasing and decreasing populations, these agents are unlikely to have been the primary cause of the population decline. They may have contributed to the decline or impeded population recovery, however, because of undetected mortality and morbidity or reductions of fecundity and body condition in animals under other stresses. Systematic monitoring for disease agents and their effects is needed to determine whether infectious disease currently plays a role in the decline and lack of recovery of Steller sea lions.

Causes of Mortality in Northern Fur Seals (Callorhinus Ursinus), St. Paul Island, Pribilof Islands, Alaska, 1986–2006

“…Hookworms did not appear to be a problem during this investigation and are therefore not a probable cause for the present decline (Lyons et al, 2000;Spraker et al, 2007). Similar to other pinniped populations inhabiting Alaskan waters that have suffered from unexplained declines, including Steller sea lions (Burek et al, 2005) and Pacific harbor seals (Phoca vitulina; Springer et al, 2003), there was no evidence to implicate other infectious diseases as a mechanism for northern fur seal decline over the past 20 yr.…”

Assessment of Clinical Pathology and Pathogen Exposure in Sea Otters (Enhydra Lutris) Bordering the Threatened Population in Alaska

“…Although caliciviruses are common marine mammal pathogens and evidence of exposure has been reported in Steller sea lions (Eumetopias jubatus) in the region (Burek et al, 2005), this pathogen does not appear to be of concern in these sea otters. The low prevalences of antibodies to T. gondii, S. neurona, and Leptospira interrogans represent a small increase in prevalence compared with those reported by Hanni et al (2003) for otters in Alaska, USA, since 1997.…”

Clinicoimmunopathologic findings in Atlantic bottlenose dolphins Tursiops truncatus with positive Chlamydiaceae antibody titers

“…However, antibodies to Chlamydophila psittaci were described in Steller sea lions Eumetopias jubatus in the northern Pacific with a seroprevalence of > 60% in adults, suggesting that Cp. psittaci, or a closely related agent, was endemic in that population (Burek et al 2005). Antibody to Cp.…”