Steller sea lion survivors: a retrospective on the impact of alternative research methods on an endangered species

Abstract

Two novel research approaches were developed to facilitate access to wild juvenile Steller sea lions. First, the Transient Juvenile Steller sea lion Project (TJ) facilitated numerous studies of physiology, behavior, and nutrition through temporary captivity (branded TJs, n=45) over the past decade. As a complement, a control group was sampled and released during capture events (FRs, n=35). Second, the Life History Tag (LHX) project was implemented within the TJ project to implant individuals (LHX-1, n=35) with internal transmitters to detect potential causes of mortality. Our goal was to evaluate the potential for long-term impacts of these two research programs on study individuals (Chapter 1) as well as identify potential metrics of survival for use in field efforts (Chapter 2). The first chapter used open-population Cormack-Jolly-Seber (CJS) mark-recapture models to project survival from resights of branded individuals in combination with demographic covariates in program MARK. TJ and FR groups were compared to identify the potential effect of temporary captivity on survival, while LHX-1 and non-implants were compared to examine a tagging effect on survival. Overall, our results mirror previous efforts to characterize survival in sea lions and indicate minimal long-term effects on mortality from research efforts, higher survival in females than males, and increasing survival rate with age. For the second chapter, a three-tiered approach to the decade of archived physiological data attempted to build links to survival in TJs through similar CJS modeling techniques. The first two levels looked at survival in relation to observed responses of handling stress through six a priori principle blood parameters measured at entry and exit. In addition, several condition indices were also incorporated into mark-recapture models, but separately considered when measured at entry and exit due to sampling inconsistencies. The third level evaluated the efficacy of single-point sampling to project similar trends for field use. Change in mass (kg) and white blood cell count (WBC, m/mm3) had the most support in predicting survival. Mass gains over captivity and slight increases in WBC resulted in a higher averaged survival rate. Minor support was identified for exit mass and entry WBC. A higher exit mass predicted a higher survival rate, while a higher entry WBC predicted a lower survival rate and may demonstrate the efficacy of single-point sampling as a management tool.