Comparing total body lipid content of young‐of‐the‐year Steller sea lions among regions of contrasting population trends

Abstract

Steller sea lion (Eumetopias jubatus) young‐of‐the‐year (YOY) are nutritionally dependent upon their dam through the majority of their first year. Several indices of body condition were measured in YOY 1.5–9 mo of age captured in Southeast Alaska (n = 122), the Gulf of Alaska (n = 182), and the Aleutian Islands (n = 38) to test the hypothesis that nutritional stress impacted the ability of adult female Steller sea lions to adequately nourish their late gestation YOY in the central Aleutian Islands in the early 2000s. Body mass (kg) and percent total body lipid content (%TBL) increased with age in all three regions of Alaska that were sampled (P < 0.05). Young‐of‐the‐year 7–9 mo of age were leaner in Southeast Alaska (27.6% ± 1.0%) and Gulf of Alaska (29.5% ± 0.8%) than in the Aleutian Islands (35.7% ± 1.2%, P < 0.001). Condition indices calculated from morphometric measures did not strongly predict the %TBL measured by isotope dilution. The trend for Aleutian Island YOY to have larger body mass and larger body fat reserves are counter to what would be expected if dams were unable to adequately provision their late lactation YOY due to inadequate food availability in the central Aleutian Islands.

Variation in milk, serum, and blubber fatty acids in young, free‐ranging Steller sea lions

“…) which on average increases to 28%–36% by 9 mo of age while the sea lions are still nutritionally dependent (Rea et al . ). In our study, season was not as influential as age on the fatty acid signature in blubber from young Steller sea lions.…”

“…, Rea et al . ). Ages were estimated based on time of year, tooth eruption, and tooth measurements using the method of King et al .…”

Overwintering Steller sea lion (Eumetopias jubatus) pup growth and behavior prior to weaning

“…However, the primary purpose of branding was to include these individuals as a cohort in a separate, range-wide long-term program to determine vital rates (i.e., survival, reproduction and To determine total body water (TBW) and ultimately the total body fat (TBF) and lean tissue mass of each pup, deuterium oxide (D 2 O) was administered intramuscularly at 0.3 -0.5 g/kg sea lion body mass and allowed to equilibrate for ≥ 2 hours (see detailed methods in Rea et al 2016). Blood (up to 1 mL/kg body mass) for subsequent laboratory analysis was collected into serum separator tubes prior to D 2 O injection and twice post-equilibration, approximately 30 minutes apart.…”

“…To determine TBF and lean tissue mass, serum samples were processed for D 2 O content as described by Rea et al (2016). TBW was calculated from the hydrogen isotope dilution space using the relationship identified by Bowen and Iverson (1998); this measurement was then used to calculate TBF and lean tissue mass following the two-step model of Reilly and Fedak (1990).…”

“…Because these growth patterns were evident the older pups and longer measurement interval of the present study, it is reasonable to conclude the rate of Steller sea lion pup growth is consistent through their first year. Other investigations of Steller sea lion growth are based on cross-sectional, single-sample data only (e.g., Winship et al 2001;Rea et al 2016). On a longer, annual timestep, Baker et al (1994) studied immature growth of another northern Otariid, the northern fur seal, and found substantial individual variability in growth rates, but overall determined individual mass growth was correlated from year-to-year through the 5 th year of age.…”