Biology subjects

Tinker, T.

Publications and source records attributed to Tinker, T..

2 recordsLinked to original sources

bioRxiv2026

Leptospirosis in Southern Sea Otters from Central California: Detection of Fatal Infections and Pathologic Findings

Leptospira interrogans serovar Pomona infections cause periodic outbreaks among California sea lions (CSL; Zalophus californianus) and sporadic deaths in phocids; however, frequency of infection and associated health impacts are uncharacterized among sympatric threatened southern sea otters (SSO; Enhydra lutris nereis), which are important sentinels of coastal health. Given the broad impacts of L. interrogans on other marine mammals, our objective was to screen selected SSO for infection, determine whether leptospirosis contributes to SSO mortality, and describe leptospiral-associated lesions. A retrospective review (2005-2025) yielded 19 candidates that underwent case review, including Leptospira immunohistochemistry (IHC), serology, and polymerase chain reaction (PCR), with a special focus on renal and hepatic lesions. Kidney was PCR-positive for 74% (14/19) of suspected cases and for eight of these, DNA sequence-based serogroup typing detected L. interrogans serogroup Pomona. Seven of the 14 PCR-positive leptospirosis cases were classed as fatal based on positive renal IHC and moderate to severe tubulointerstitial nephritis. All fatal cases had anti-L. interrogans serovar Pomona antibody titers [≥]1:25,600. All remaining (n=7) PCR-positive cases were considered nonfatal leptospirosis cases due to minimal and/or unrelated renal lesions, and negative IHC. Nonfatal Leptospira-infected cases ranged from seronegative to low positive (1:400) for serovar Pomona. Antibody titers for Leptospira PCR-negative cases were negative. For fatal cases, gross renal changes were often inapparent or characterized by miliary white cortical foci. Renal histologic lesions included tubulointerstitial nephritis, acute tubular necrosis and suppurative tubulitis with intratubular bacteria in fatal cases, and positive IHC staining for leptospiral antigen in lesions. Gross hepatic changes were also inapparent in fatal cases and histologic lesions were rare, characterized in one animal by hepatocellular disassociation and in two sea otters by limited leptospiral antigen detection by IHC. Most Leptospira-infected sea otters (71%, 10/14) stranded during higher rainfall months in California, suggesting possible land-to-sea transmission from terrestrial hosts. Given these findings, and because L. interrogans serovar Pomona infections have been confirmed in sympatric CSLs and terrestrial mammals from adjacent watersheds, focused investigation of potential marine and terrestrial disease transmission dynamics could provide new information to reduce mortalities of SSO.

pathology↗

bioRxiv2023

The combined impact of killer whale consumptive and non-consumptive effects on northern sea otter population viability in the Western Aleutians Archipelago, Alaska

Predators can alter the abundance, distribution, and behavior of prey populations through consumptive and non-consumptive effects. In the Aleutian Archipelago of Alaska, killer whales (Orcinus orca) are considered the most probable cause of northern sea otter (Enhydra lutris kenyoni) population declines in the southwestern Alaska stock, which led to their listing as a threatened distinct population segment under the Endangered Species Act. Much of the research attention in the Aleutian Archipelago region has focused on the consumptive effects of killer whales on sea otter population dynamics. Here, we explore non-consumptive effects by accounting for restricted sea otter habitat use within discrete predation refuges characterized by areas of shallow, complex reef habitats close to shore. We constructed Population Viability Analysis (PVA) models that incorporated sea otter count data collected by aerial and skiff-based methods over six decades (1959 - 2021) to inform uplisting (to endangered) and downlisting (delisting from ESA) criteria. Our models incorporated both density-dependent effects and density-independent effects on sex and age structure, which we termed predation hazards. Prior to 1990, predation hazards were negligible, fluctuated at high values between 1990 and the early 2000s, and then declined as sea otter populations reached low densities. We estimated a current regional abundance of 2,405 sea otters (95%CI = 1,734 - 3,238) in the Western Aleutians Management Unit. Our base PVA model that considered only inter-island fragmentation indicated the risk of the regional sea otter population becoming endangered was <5% when there were at least 1,500 otters (95%CI = 1,200 - 2,100), and provided a delisting threshold of 2,100 sea otters. A PVA model that accounted for restricted habitat use of sea otters within discrete predation refuges (i.e. inter-island and intra-island fragmentation) indicated a less encouraging potential for sea otter recovery. The probability of the population becoming endangered increased to >10% and the delisting threshold increased to >10,000 sea otters (nearly 5x higher). Our results indicate sea otters within fragmented predation refuges could be more susceptible to the effects of stochastic processes with potentially limited ability for rescue effects. Overall, our research reveals the importance of evaluating both consumptive and non-consumptive effects when considering conservation and management plans for at-risk populations thought to be limited by a predator.

ecology↗