Abstract
The Steller sea lion, Eumetopias jubatus, has experienced regionally divergent population trends over recent decades. One potential mechanism for this disparity is that local factors cause reduced health and, therefore, reduced survival of individuals. The use of blood parameters to assess sea lion health may help to identify whether malnutrition, disease and stress are important drivers of current trends, but such assessments require species-specific knowledge of how parameters respond to various health challenges. We used principal components analysis to identify which key blood parameters (principal analytes) best described changes in health for temporarily captive juvenile Steller sea lions in known conditions. Generalized additive mixed models were used to estimate the changes in principal analytes with food intake, time in captivity and acute trauma associated with hot-iron branding and transmitter implant surgery. Of the 17 blood parameters examined, physiological changes for juvenile sea lions were best described using the following six principal analytes: red blood cell counts, white blood cell counts, globulin, platelets, glucose and total bilirubin. The white blood cell counts and total bilirubin declined over time in captivity, whereas globulin increased. Elevated red blood cell counts, white blood cell counts and total bilirubin and reduced globulin values were associated with lower food intake. After branding, white blood cell counts were elevated for the first 30 days, while globulin and platelets were elevated for the first 15 days only. After implant surgery, red blood cell counts and globulin remained elevated for 30 days, while white blood cell counts remained elevated during the first 15 days only. Glucose was unassociated with the factors we studied. These results were used to provide expected ranges for principal analytes at different levels of food intake and in response to the physical challenges of branding and implant surgery. These results provide a more detailed reference for future evaluations of health-related assessments.
Highlights
Steller sea lions (Eumetopias jubatus) in the USA have followed different trajectories across their range over the past few decades
The western distinct population segment remains listed as endangered under the Endangered Species Act, but the eastern distinct population segment, which was previously categorized as threatened, has been delisted
E. jubatus, aged 12–24 months based on tooth eruption patterns (King et al, 2007) were captured in 13 groups from Prince William Sound, AK, USA, between August 2003 and May 2009
Summary
Steller sea lions (Eumetopias jubatus) in the USA have followed different trajectories across their range over the past few decades. The population was divided into the western and the eastern distinct population segments at 144° West longitude (Cape Suckling, AK, USA). The western distinct population segment experienced a 70%. 1960s (Merrick et al, 1995), whereas the genetically distinct. The western distinct population segment remains listed as endangered under the Endangered Species Act, but the eastern distinct population segment, which was previously categorized as threatened, has been delisted The underlying causes for these divergent population trends remain unclear
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