The Effect of Novel Research Activities on Long-term Survival of Temporarily Captive Steller Sea Lions (Eumetopias jubatus)

Abstract

Two novel research approaches were developed to facilitate controlled access to, and long-term monitoring of, juvenile Steller sea lions for periods longer than typically afforded by traditional fieldwork. The Transient Juvenile Steller sea lion Project at the Alaska SeaLife Center facilitated nutritional, physiological, and behavioral studies on the platform of temporary captivity. Temporarily captive sea lions (TJs, n = 35) were studied, and were intraperitoneally implanted with Life History Transmitters (LHX tags) to determine causes of mortality post-release. Our goal was to evaluate the potential for long-term impacts of temporary captivity and telemetry implants on the survival of study individuals. A simple open-population Cormack-Jolly-Seber mark-recapture model was built in program MARK, incorporating resightings of uniquely branded study individuals gathered by several contributing institutions. A priori models were developed to weigh the evidence of effects of experimental treatment on survival with covariates of sex, age, capture age, cohort, and age class. We compared survival of experimental treatment to a control group of n = 27 free-ranging animals (FRs) that were sampled during capture events and immediately released. Sex has previously been show to differentially affect juvenile survival in Steller sea lions. Therefore, sex was included in all models to account for unbalanced sex ratios within the experimental group. Considerable support was identified for the effects of sex, accounting for over 71% of total weight for all a priori models with delta AICc <5, and over 91% of model weight after removal of pretending variables. Overall, most support was found for the most parsimonious model based on sex and excluding experimental treatment. Models including experimental treatment were not supported after post-hoc considerations of model selection criteria. However, given the limited sample size, alternate models including effects of experimental treatments remain possible and effects may yet become apparent in larger sample sizes.

Wanted dead or alive: characterizing likelihood of juvenile Steller sea lion predation from diving and space use patterns

“…The links between individuals' behaviors and mortality have been explored in laboratory and terrestrial settings (Jones & Godin 2010, Réale & Festa-Bianchet 2003, but there is a considerable lack of empirical studies in marine ecosystems (Hays et al 2016). While the fate of individuals in marine environments is commonly tracked via mark-recapture efforts (Shuert et al 2015), observations of predation events have been labeled as 'empirically intractable' (Williams et al 2004) for marine vertebrates. Due to this absence of observed mortalities, most of our understanding of the predator−prey dynamics in marine ecosystems focuses on non-consumptive effects through theoretical models of resource and risk trade-offs (Frid et al 2006) and behavioral assessments of how risk shapes animals' movements and space use (Hammerschlag et al 2015, Breed et al 2017.…”

Best practice recommendations for the use of fully implanted telemetry devices in pinnipeds

“…Long-term survival beyond the attachment of external transmitters was compared between implanted animals and non-implanted controls that did not undergo captivity, based on a mark-resight study design using hot-iron branding. No differences in survival patterns between implanted animals and nonimplanted controls were detectable between the ages of 14 months to five years [65]. From the ratio of dual-to single-tag data returns in 20 mortalities detected to date (through 2016) and in 10 dual-tag carcass simulations, data return probability was estimated at >0.98 [49].…”

“…Furthermore, some effects may have low-level accumulating impacts that may become more detectable when integrated over longer periods of time [11,100]. While short-and medium-term effects may be studied at the level of proximate mechanisms, long-term effects can more readily be assessed via ultimate impacts on growth, migration, reproduction and survival (e.g., [65]). It is inappropriate to assume that FITs will not affect data or subjects simply based on size or mass percentages (see recommendation #3) or based on demonstrated absence of effects in other species carrying similar devices.…”

Why implantation of bio‐loggers may improve our understanding of how animals cope within their natural environment

“…To date, few studies have investigated the effect of device implantation on wild animals over multiple years. For example, Shuert et al (2015) investigated the effect of temporary captivity and the implantation of a life history tag into the body cavity of juvenile Steller sea lions on survival over a period of 4 years. Survival over that period did not differ between these experimental animals and control animals that were captured and marked at the same time but released immediately after.…”

“…Implantable temperature probes (Handrich et al 1997;Schmidt et al 2006;Eichhorn et al 2011) and externally attached heat flux sensors (Willis & Horning 2005) allow the detailed study of thermoregulatory aspects of animals. Loggers interfaced with chemical electrodes that record oxygen partial pressure (P O2 ) and the use of implantable near-infrared spectrophotometer (NIRS) probes (recording muscle O 2 saturation) more recently helped to shed some light onto the mystery of how expert divers, like emperor penguins (Aptenodytes forsteri), meticulously manage their finite oxygen stores during diving, enabling them to dive for extended periods and to great depth (Stockard et al 2005;Ponganis et al 2007;Williams et al 2011).…”