Neonatal survival of Steller sea lions (Eumetopias jubatus)

Neonatal survival of Steller sea lions ( Eumetopias jubatus ) are often considered inconsequential to their population dynamics. However, observations of dead animals on rookeries and in surrounding waters suggest that early mortality is not uncommon. This study used the natural markings of adult females in a mark and resighting framework to estimate the apparent survival (φ) of pups with the Cormack–Jolly–Seber model at two sites on Lowrie Island, Alaska from birth to 3 wk old. Estimates varied greatly by site and year; 2002 Area 5:     (95% CI: 0.199, 0.684; n = 21), 2002 Area 1:     (0.437, 0.916; n = 21), 2003 Area 5:     (0.414, 0.738; n = 56), and 2003 Area 1:     (0.695, 0.997; n = 32). The mean estimate across the four area × year combinations was     (0.569, 0.772). Survival was lowest on the first day of life and then leveled off at a higher rate. None of the four environmental covariates we considered (swell height, interaction of tide and swell heights, density, or birth date) were significantly related to neonatal survival. Our results suggest that estimates of first-year survival that do not account for mortality prior to dispersal from the natal rookery may significantly overestimate survival rate.     

Characterization of eight microsatellite loci in Steller sea lions (Eumetopias jubatus)

Steller sea lions (Eumetopias jubatus) are listed as an endangered species in western Alaska and have exhibited a significant population decline throughout their range. Eight microsatellite loci were isolated from genomic DNA libraries. In addition, all these markers were found to be variable in nine individuals of the California sea lion (Zalophus californicus). This panel of markers was developed to analyse population structure in Steller sea lions throughout their range.     

Foraging behavior of adult female Steller sea lions during the breeding season in Southeast Alaska

During the 1990s, the Steller sea lion ( Eumetopias jubatus Schreber) Western Alaska stock (WS) suffered steep population decline while the Eastern Alaska stock (ES) steadily increased. One bottom-up forcing hypothesis explaining this decline predicted lactating adult female foraging behavior would be different between stocks. To investigate this effect, we monitored 11 ES females at two breeding rookeries using satellite dive recorders (SDR) during the early breeding seasons of 1992–1993, examined their behavior with respect to prey, physiological limitations, and habitat, and made limited comparisons to observations of WS female behavior reported in the literature. ES females were not operating at the extremes of ability, with most diving within the limits of aerobic metabolism, less than one-quarter of possible foraging time during trips spent submerged and most foraging trips requiring less than one-half the lipid store fasting ability of dependent pups. Thus, females may have some capacity to alter behavior to accommodate future changes in foraging conditions, but the extent of this plasticity is unknown. Because recent work suggests WS recovery is impeded by low natality, future studies should test differences between reproductive and non-reproductive mature females in order to properly assess the contribution of foraging ecology to SSL population dynamics.     

Temporal variability in organochlorine contamination in blood and blubber of captive Steller sea lions (Eumetopias jubatus)

Three adult captive Steller sea lions (SSL; two females, one male) housed in Alaska were longitudinally sampled for organochlorine contaminant (OC) analysis in both blubber (n= 19) and blood (n= 69) over a 2 yr period (March 2001 to March 2003). Blood OC concentrations were similar between individuals, and exhibited significant increases in summer months (July through September) relative to winter (January through March). Additionally, paired blood and blubber sample (n= 18) OC were significantly related for all animals. The relationship of blubber OC concentrations to lipid content was significant in all animals. Although limited to a small number of animals, our study results indicate that in SSLs, blood OC were both consistent among all animals and likely changed in association with physiologically driven metabolism of blubber.     

Effects of research disturbance on the behavior and abundance of Steller sea lions (Eumetopias jubatus) at two rookeries in Alaska

We examined the effects of research disturbance on the behavior and abundance of Steller sea lions (Eumetopias jubatus) at rookeries on Marmot and Ugamak Islands in Alaska. During 3 of 6 yr, researchers intentionally drove all adult and juvenile sea lions off at least part of the beach in order to permanently mark and measure sea lion pups. The research disturbance occurred after the majority of females had bred and when most pups were 1 mo old. We used generalized linear models to determine the relationship between research disturbance and sea lion behavior or abundance. Research disturbance was related to changes in the proportion of sea lions exhibiting two to three of nine behavior metrics: agonistic and resting females and active males at Marmot, and active and resting males and females at Ugamak. Model results indicated that changes lasted between 3 and 20 d depending on the sex, behavior, and rookery. Inclusion of research disturbance into Marmot abundance models did not improve the fit to the data, if variability between years was permitted. Optimally timed, low‐frequency research disturbance did not appear to have long‐term effects on sea lion behavior or abundance and was largely associated with changes that were similar to natural variation.     

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

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.     

Age‐specific vibrissae growth rates: A tool for determining the timing of ecologically important events in Steller sea lions

Steller sea lions (SSL; Eumetopias jubatus) grow their vibrissae continually, providing a multiyear record suitable for ecological and physiological studies based on stable isotopes. An accurate age‐specific vibrissae growth rate is essential for registering a chronology along the length of the record, and for interpreting the timing of ecologically important events. We utilized four methods to estimate the growth rate of vibrissae in fetal, rookery pup, young‐of‐the‐year (YOY), yearling, subadult, and adult SSL. The majority of vibrissae were collected from SSL live‐captured in Alaska and Russia between 2000 and 2013 (n = 1,115), however, vibrissae were also collected from six adult SSL found dead on haul‐outs and rookeries during field excursions to increase the sample size of this underrepresented age group. Growth rates of vibrissae were generally slower in adult (0.44 ± 0.15 cm/mo) and subadult (0.61 ± 0.10 cm/mo) SSL than in YOY (0.87 ± 0.28 cm/mo) and fetal (0.73 ± 0.05 cm/mo) animals, but there was high individual variability in these growth rates within each age group. Some variability in vibrissae growth rates was attributed to the somatic growth rate of YOY sea lions between capture events (P = 0.014, r² = 0.206, n = 29).     

Organochlorine exposure and health effects in stranded Steller sea lions (Eumetopias jubatus) and Pacific harbor seals (Phoca vitulina richardii) from Oregon and southern Washington coasts

Organochlorine (OC) pesticides and polychlorinated biphenyls (PCBs) have been detected in a variety of marine mammal species at levels associated with adverse health effects. Little is known about OC levels and impacts on health in pinnipeds with different life histories. We determined the health and levels of 18 OC pesticides and 16 PCB congeners in blubber samples from 20 Steller sea lions and 39 Pacific harbor seals stranded from Oregon and Southern Washington. The most commonly detected OC at the highest concentration was p,p′- dichlorodiphenyldichloroethylene (DDE). PCBs were detected in all samples as well. Hypothesis testing indicated that diseased Steller sea lions (males and females combined) had higher contaminant concentrations than healthy Steller sea lions, and diseased Pacific harbor seals had higher concentrations of total OCs than healthy animals. Differences were also noted between diseased and healthy animals when looking at individual sexes of each species. Diseased Steller sea lions had higher mean contaminant levels than diseased harbor seals and healthy Steller sea lions had higher mean contaminant concentrations than healthy Pacific harbor seals. These results show that species differences exist in both contaminant loads and sensitivity to contaminants, which may be due to differences in life histories and physiology.     

The role of Steller sea lions in a large population decline of harbor seals

We provide the first direct evidence that Steller sea lions will prey on harbor seals. Direct observations of predation on marine mammals at sea are rare, but when observed rates of predation are extrapolated, predation mortality may be found to be significant. From 1992 to 2002, harbor seals in Glacier Bay declined steeply, from 6,200 to 2,500 (∼65%). After documenting that Steller sea lions were preying on seals in Glacier Bay, we investigated increased predation by sea lions as a potential explanation for the large decline. In five independent data sets spanning 21–25 yr and including 14,308 d of observations, 13 predation events were recorded. We conducted a fine-scale analysis for an intensively studied haul-out (Spider Island) and a broader analysis of all of Glacier Bay. At Spider Island, estimated predation by sea lions increased and could account for the entirety of annual pup production in 5 of 8 yr since 1995. The predation rate, however, was not proportional to the number of predators. Predation by Steller sea lions is a new source of mortality that contributed to the seal declines; however, life history modeling indicates that it is unlikely that sea lion predation is the sole factor responsible for the large declines.     

Crossing to safety: dispersal,colonization and mate choice in evolutionarily distinct populations of Steller sea lions,Eumetopias jubatus

Population growth typically involves range expansion and establishment of new breeding sites, while the opposite occurs during declines. Although density dependence is widely invoked in theoretical studies of emigration and colonization in expanding populations, few empirical studies have documented the mechanisms. Still fewer have documented the direction and mechanisms of individual transfer in declining populations. Here, we screen large numbers of pups sampled on their natal rookeries for variation in mtDNA (n = 1106) and 16 microsatellite loci (n = 588) and show that new Steller sea lion breeding sites did not follow the typical paradigm and were instead colonized by sea lions from both a declining (Endangered) population and an increasing population. Dispersing individuals colonized rookeries in the distributional hiatus between two evolutionarily distinct ( = 0.222,  = 0.053, K = 2) metapopulations recently described as separate subspecies. Hardy–Weinberg, mixed‐stock and relatedness analysis revealed levels of interbreeding on the new rookeries that exclude (i) assortative mating among eastern and western forms, and (ii) inbreeding avoidance as primary motivations for dispersal. Positive and negative density dependence is implicated in both cases of individual transfer. Migration distance limits, and conspecific attraction and performance likely influenced the sequence of rookery colonizations. This study demonstrates that resource limitation may trigger an exodus of breeding animals from declining populations, with substantial impacts on distribution and patterns of genetic variation. It also revealed that this event is rare because colonists dispersed across an evolutionary boundary, suggesting that the causative factors behind recent declines are unusual or of larger magnitude than normally occur.     

Ontogeny of total body oxygen stores and aerobic dive potential in Steller sea lions (Eumetopias jubatus)

Two key factors influence the diving and hence foraging ability of marine mammals: increased oxygen stores prolong aerobic metabolism and decreased metabolism slows rate of fuel consumption. In young animals, foraging ability may be physiologically limited due to low total body oxygen stores and high mass specific metabolic rates. To examine the development of dive physiology in Steller sea lions, total body oxygen stores were measured in animals from 1 to 29 months of age and used to estimate aerobic dive limit (ADL). Blood oxygen stores were determined by measuring hematocrit, hemoglobin, and plasma volume, while muscle oxygen stores were determined by measuring myoglobin concentration and total muscle mass. Around 2 years of age, juveniles attained mass specific total body oxygen stores that were similar to those of adult females; however, their estimated ADL remained less than that of adults, most likely due to their smaller size and higher mass specific metabolic rates. These findings indicate that juvenile Steller sea lion oxygen stores remain immature for more than a year, and therefore may constrain dive behavior during the transition to nutritional independence.     

Body mass and composition responses to short-term low energy intake are seasonally dependent in Steller sea lions (Eumetopias jubatus)

Steller sea lions (Eumetopias jubatus) were fed restricted iso-caloric amounts of Pacific herring (Clupea pallasi) or walleye pollock (Theragra chalcogramma) for 8–9 days, four times over the course of a year to investigate effects of season and prey composition on sea lion physiology. At these levels, the sea lions lost body mass at a significantly higher rate during winter (1.6 ± 0.14 kg day⁻¹), and at a lower rate during summer (1.2 ± 0.32 kg day⁻¹). Decreases in body fat mass and standard metabolic rates during the trials were similar throughout the seasons and for both diet types. The majority of the body mass that was lost when eating pollock derived from decreases in lipid mass, while a greater proportion of the mass lost when eating herring derived from decreases in lean tissue, except in the summer when the pattern was reversed. Metabolic depression was not observed during all trials despite the constant loss of body mass. Our study supports the hypothesis that restricted energy intake may be more critical to Steller sea lions in the winter months, and that the type of prey consumed (e.g., herring or pollock) may have seasonally specific effects on body mass and composition.     

Effects of increased swimming costs on foraging behavior and efficiency of captive Steller sea lions: Evidence for behavioral plasticity in the recovery phase of dives

A significant component of foraging energetics is the cost of locomotion, which for marine animals, is the cost of swimming. Increases in the cost of swimming may have significant impacts on foraging efficiency. Minimizing the cost of swimming can contribute to the optimization of foraging strategies by reducing the energetic cost of foraging. Results of several field studies suggest that an increase in the cost of locomotion may have comparable effects on foraging behavior and efficiency to a decrease in prey availability. We tested the hypothesis that an increased cost of swimming, brought on by increased hydrodynamic drag, has the same effect on dive behavior and efficiency as reduced prey availability under standard locomotion. Experiments were performed using two adult female Steller sea lions at the Alaska SeaLife Center in Seward, AK, using the same animals and general experimental design previously used to test the effects of reduced prey encounter rate on dive behavior and efficiency. Animals were fitted with a drag-inducing harness for half of the 500 simulated foraging dives in order to increase the cost of swimming. Individual dive duration and foraging time were significantly reduced in all cost-increased dives, comparable to the effects of reduced prey encounter rate. However, on a bout-by-bout basis, dive and foraging efficiency were only slightly reduced, which is likely due to an average 50% reduction in post-dive surface recovery duration during cost-increased dives. Increased heat flux across the body surface measured in a parallel study confirmed a significant increase in work during drag-increased dives. These results suggest that sea lions are able to compensate for changes in the cost of foraging and maintain their foraging efficiency by altering their dive strategy over an entire bout of dives when operating well within their aerobic scope.     

Alloparenting in Steller sea lions (<Emphasis Type="Italic">Eumetopias jubatus</Emphasis>): correlations with misdirected care and other observations

Alloparental care is rarely observed in Steller sea lions (Eumetopias jubatus) where maternal care is extended to a single pup for up to 1 year or more. However, we observed 28 allonursing events and one case of adoption at a small breeding rookery in the western Gulf of Alaska between the years 2001 and 2005. Multiparous and primiparous females were observed nursing nonfilial individuals with equal frequency, but primiparous females spent significantly more time nursing nonfilial individuals. Multiparous females allowed allonursing only while sleeping and unaware while most primiparous females were aware that they were allonursing. These results are consistent with the misdirected-care hypothesis suggesting that primiparous (presumably younger) females nurse nonfilial pups due to inexperience, whereas multiparous (presumably older) females are victims of milk stealing during times of inattentiveness. Nonfilial pups were aggressively tossed most often during the pupping season and only by multiparous females, while allonursing events occurred more frequently after the pupping season. Starveling pups were not cared for by any female, but two were attended by a single bull during separate autumn seasons.     

Trace elements in the teeth of Steller sea lions (<Emphasis Type="Italic">Eumetopias jubatus</Emphasis>) from the North Pacific

The occurrence of trace elements in the teeth of Steller sea lions (Eumetopias jubatus) collected from the North Pacific from 1968 to 1999 is described. Using particle-induced X-ray emission analysis, we detected eight trace elements: Ca, Mn, Fe, Cu, Zn, Br, Sr and Pb. We used a general linear model to evaluate long-term trends of trace element accumulation. Zn (Zn/Ca) and Fe (Fe/Ca) levels both varied during the last three decades, and showed significant differences between animals of different age (Fe/Ca), season (Zn/Ca and Fe/Ca), and sex (Zn/Ca); both Zn/Ca and Fe/Ca ratios were higher in young males than older males. Pb was detected in 39% of the samples from Hokkaido (Japan) and 22% of those from Alaska. The high levels of Pb recorded in 1975 were thought to be related to the use of leaded gasoline during the 1970s. Our results indicate that the levels of trace elements in the teeth of Steller sea lions can be used as indicators of temporal and spatial variations of trace element pollution.     

Interactions between killer whales (<Emphasis Type="Italic">Orcinus orca</Emphasis>) and Steller sea lions (<Emphasis Type="Italic">Eumetopias jubatus</Emphasis>) in the vicinity of Brat Chirpoev Island,Kuril Islands

The behaviors of breeding Steller sea lions in response to encounters with killer whales near the shore were observed on Brat Chirpoev Island, Kuril Islands between May and July 2002–2007. Approaches by killer whales and sea lion behavior was observed visually and recorded. Killer whales approached the rookery 104 times during the entire period of observations (289 days). In most cases (n = 95), beached sea lions did not show any apparent reactions to the presence of killer whales, and there were no observed interactions. Sea lions showed agitation during nine of the approaches; five of these events were considered to be predation attempts. The killer whales attacked the sea lions three times, however all the attacks were unsuccessful. We recorded two different types of responses towards the killer whales: (1) beaching on the shore (three times) and (2) mass exodus from the rookery with subsequent formation of a tight, actively swimming and vocalizing group (six times). The latter is the first recorded observation of this behavior for Steller sea lions. The observation suggests a low degree of interactions between these two species near the studied rookery. Despite the numerous observations of killer whales near the rookery, there were no observations of direct predation on sea lions. It is likely the killer whale predation has little or no direct impact on the Steller sea lion population on Brat Chirpoev Islands during the breeding period.     

Steller sea lion spatial‐use patterns derived from a Bayesian model of opportunistic observations

Despite acquisition of a substantial catalog of telemetry data from Steller sea lions (Eumetopias jubatus) over the past two decades, scientists still lack comprehensive regionally explicit knowledge about Steller sea lion habitat use. The Platforms of Opportunity data contain records of Steller sea lion sightings throughout the species’ entire range and have potential to fill gaps in knowledge about their spatial use; however, the data have not previously been used because effort (e.g., time spent surveying or area sampled) was not recorded when sightings were obtained. For this study a novel approach was used to overcome the lack of effort data through development of an effort index and a Bayesian negative binomial model. The model quantified Steller sea lion encounter rates and associated uncertainty within 15 × 15 km² grid cells across the species’ entire range. Year‐round, as well as breeding and nonbreeding season encounter rates were estimated. The results of this analysis identify several previously undocumented areas of high use by Steller sea lions, indicate that only 37% of Steller sea lion high‐use areas fall within designated critical habitat, and demonstrate that use of depth and distance from shore as indicators of Steller sea lion habitat is contraindicated.