Serum estradiol and progesterone profiles during estrus, pseudopregnancy, and active gestation in Steller sea lions.

While the proximate driver behind the decline of the Western stock of Steller sea lions (Eumetopias jubatus, >80% since 1970s) is likely multifactorial, the population reduction may have been powered by a decrease in fecundity. A harvest of Steller sea lions in the 1970s and 80s revealed a 30% reduction in the proportion of pregnant females from early (October-November) to late gestation (April-May). Identification and quantification of these reproductive failures are difficult when we lack species-specific data on endocrinology associated with discrete stages of the reproductive cycle (i.e., estrus, implantation, and gestation). We tracked changes in serum estradiol and progesterone in three adult female Steller sea lions from 2011 to 2015. In all years and most females, a discrete increase in estradiol was observed during the breeding season (June-August), indicative of estrus. Estradiol concentrations from October to May in a pregnant female compared to her corresponding values when non-pregnant did not consistently differ through gestation. An elevation in progesterone was observed in all females and all years beginning approximately in June and lasting through November. This likely results from progesterone production by the corpus luteum in both pregnant and pseudopregnant females. Serum progesterone shows promise as a diagnostic tool to identify pregnancy during months 3-5 (December-February) of the 8-month active gestation following embryonic implantation. This study provides ranges of key hormones during estrus, embryonic diapause/pseudopregnancy, and gestation in pregnant and non-pregnant females for studying reproduction in Steller sea lions.

Dive, food, and exercise effects on blood microparticles in Steller sea lions (Eumetopias jubatus): exploring a biomarker for decompression sickness.

Recent studies of stranded marine mammals indicate that exposure to underwater military sonar may induce pathophysiological responses consistent with decompression sickness (DCS). However, DCS has been difficult to diagnose in marine mammals. We investigated whether blood microparticles (MPs, measured as number/µl plasma), which increase in response to decompression stress in terrestrial mammals, are a suitable biomarker for DCS in marine mammals. We obtained blood samples from trained Steller sea lions (Eumetopias jubatus, 4 adult females) wearing time-depth recorders that dove to predetermined depths (either 5 or 50 meters). We hypothesized that MPs would be positively related to decompression stress (depth and duration underwater). We also tested the effect of feeding and exercise in isolation on MPs using the same blood sampling protocol. We found that feeding and exercise had no effect on blood MP levels, but that diving caused MPs to increase. However, blood MP levels did not correlate with diving depth, relative time underwater, and presumed decompression stress, possibly indicating acclimation following repeated exposure to depth.

Seasonal variability in otariid energetics: implications for the effects of predators on localized prey resources.

Otariids, like other wild mammals, contend with a wide variety of energetic demands across seasons. However, due to the cryptic behaviors of this marine group, few studies have been able to examine longitudinal energetic costs or the potential impact of these costs on seasonal or annual prey requirements. Here we evaluated the changes in energy demand and intake of female California sea lions (Zalophus californianus) during reproductive (n=2 sea lions) and nonreproductive (n=3) periods. Monthly measurements included resting metabolic rate, blood hormone levels, body condition (blubber thickness and body mass), and caloric intake for adult sea lions throughout molting, late pregnancy, lactation, and postweaning. We found that maintenance energy demands decreased from 32.0 to 23.1 MJ d(-1) before pupping, remaining stable at 19.4+/-0.6 MJ d(-1) during lactation and postweaning. Energy intake rates to meet these demands showed marked changes with activity level and the reproductive cycle, reaching a peak intake of 3.6 times baseline levels during lactation. Translating this into prey demands, we find that 20,000 reproductively active females on San Nicolas Island rookeries would maximally require 4,950 metric tons of Pacific whiting during a month of the breeding season. This localized impact is reduced significantly with postbreeding dispersal and demonstrates the importance of considering spatial and temporal factors driving the energetic requirements of predators when designing marine protected areas.

Fingerprint of polycyclic aromatic hydrocarbons in two populations of southern sea lions (Otaria flavescens).

The fingerprint of 14 polycyclic aromatic hydrocarbons (PAHs) was investigated in biopsy, fur, blood, liver and faeces of live and dead specimens of two Argentinian population of southern sea lion (Otaria flavescens). One colony lives in Mar del Plata harbour which is particularly polluted with petroleum, the second (control) colony lives at Punta Bermeja (Patagonia). The highest concentrations of the five carcinogenic PAHs were found in the Mar del Plata sea lions.

Evidence for a prolonged postimplantation period in the Australian sea lion (Neophoca cinerea).

Concentrations of circulating progesterone and oestradiol were measured in 96 free-ranging, female Australian sea lions Neophoca cinerea from Kangaroo Island, South Australia. There was a marked increase in the concentrations of both hormones (progesterone from approximately 12 ng ml-1 to approximately 24 ng ml-1; oestradiol from approximately 1.5 pg ml-1 to approximately 14 pg ml-1) about 3.5 months after the probable date of mating, reaching peak values in the 5 months after parturition. Progesterone concentrations remained at peak concentrations for about 2 months, decreasing at approximately 8 months to concentrations approximating those of the first 3 months after parturition. Oestradiol concentrations decreased, after reaching a peak, to 3-4 pg ml-1 at about 8 months after parturition. The timing of the increase in the concentrations of circulating progesterone and oestradiol provides evidence that the blastocyst reactivates and implants between 3.5 and 5 months of pregnancy in Australian sea lions, indicating an embryonic diapause of similar duration to that of other pinnipeds. This would suggest a prolonged postimplantation period of up to 14 months (to fit with the gestation period of 18 months reported for this species) the longest postimplantation period recorded for pregnancy in any pinniped.