Maternal attendance patterns of Steller sea lions ( Eumetopias jubatus ) from stable and declining populations in Alaska

Canadian Journal of Zoology (Impact Factor: 1.5). 01/2003; 81(2):340-348. DOI: 10.1139/z03-008

ABSTRACT Maternal attendance patterns of Alaskan Steller sea lions (Eumetopias jubatus) were compared during the summer breeding seasons in 1994 and 1995 at Sugarloaf Island (a declining population) and Lowrie Island (a stable population). Our goal was to determine whether there were differences in maternal attendance between the two popula- tions that were consistent with the hypothesis that lactating Steller sea lions in the area of decline were food-limited during summer. Our a priori expectations were based on well-documented behavioural responses of otariids to reduced prey availability. We found that foraging trips were significantly shorter in the area of population decline, counter to initial predictions. The mean length of foraging trips in the declining area was 19.5 h compared with 24.9 h in the sta - ble area. In contrast, the mean perinatal period (time between parturition and first feeding trip) was significantly longer in the area of decline (9.9 versus 7.9 days), again countering initial predictions. The mean length of shore visits for the declining population was also significantly longer (27.0 h compared with 22.6 h where the population was stable). For both populations, the mean time that mothers foraged increased as pups grew older, whereas the time that they spent on shore with their pups became shorter. Behavioural observations of maternal attendance patterns are inconsistent with the hypothesis that lactating Steller sea lions from the declining population had difficulty obtaining prey during summer.

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    ABSTRACT: The New Zealand (NZ) sea lion, Phocarctos hookeri, is endemic to NZ and listed as threatened and nationally critical. It was extirpated from mainland NZ by the 1800s and it has only started recolonising part of its historical breeding range, the Otago Peninsula (OP), since the 1990s. This recolonisation has opened two areas of research: 1) data were needed for the management of interactions between humans and sea lions at sea and for marine habitat protection around the OP, and 2) comparison of data between the only three remnant breeding areas in the sub-Antarctic islands (hypothesised as marginal habitat) and the recolonising population. This thesis presents the results of the first study into the foraging ecology of the small recolonising population of female NZ sea lions inhabiting the OP. Up to 2010, 45 pups had been born at the OP, all descendants from a unique matriarch that emigrated from the sub-Antarctic North Auckland Islands (AI) breeding colony. During autumns 2008 to 2010, the foraging ecology, diet and condition of 13 female NZ sea lions born on the OP (all known-to-be alive ≥ 2 years old, including six during two different years) were investigated. They foraged within a small area around the OP (mean shore distance 4km), predominantly on shallow rocky reefs (<30m depth) and in the area of bryozoan thickets in deeper waters (50-100m depth). Their diving behaviour qualified them as some of the shallowest diving otariids (mean dive depth 20m). Two prey of medium-to-high-energy content (barracouta, Thyrsites atun, and jack mackerel, Trachurus sp.) made up approximately 60% of the diet of female NZ sea lions, although individual specialisations were identified. Pup growth and mass, body mass index and milk fat content all had values in the highest ranges reported for otariids and there was no indication of serious disease or parasite infection. From 2008 to 2010, weekly surveys of female NZ sea lions presence on the OP showed that they are likely permanent residents on the OP. Combined with calculated inter-annual foraging site fidelity, it enabled the descriptions of areas of potential by-catch risk in fisheries around the OP. A technique using decoys was developed to possibly orientate immigrating females to join the existing group and limit areas of interactions, at least during the start of this recolonisation. The recolonising population of female NZ sea lions on the OP exploits what appear to be abundant, easily accessible and high-energy food resources. Age was not a significant factor in explaining any foraging parameters, and foraging effort did not correlate to energy content of prey. This accentuated the suitability of the habitat around the OP for NZ sea lions. This is in contrast with results for the females in the AI that are the deepest and longest diving otariids, feed on lower energy prey and have lower condition than OP females. The results of this thesis corroborate the hypothesis that the AI are marginal marine habitat for this species. Current large-scale fisheries there may be depleting the already limited food resources and reducing the carrying capacity of the marine habitat. Management needs to address the marginality of the habitat to ensure the survival of the remnant populations. Management of the recolonisation of NZ sea lions onto mainland NZ needs to focus on public education, marine habitat protection, monitoring potential competition and determining if by-catch has been unreported. Given the importance of this population for the recovery of the NZ sea lion, a protected area covering the main foraging habitats of female NZ sea lions appears to be the best option to ensure its establishment. Regular monitoring of pup mass, diet and population numbers of sea lions and other large marine predators should increase our understanding of the impact of recolonisation to the habitat, and potential issues that need to be managed. The results presented in this thesis constitute the baseline of foraging ecology and condition for this population and are available to help manage and document the recolonsiation for future management needs in other areas where the NZ sea lion may return.
    01/2011, Degree: PhD, Supervisor: Lloyd Davis, Louise Chilvers, Antoni Moore
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    ABSTRACT: Steller sea lions were listed as endangered following a collapse of the western distinct population beginning in the late 1970s. Low juvenile survival has been implicated as a factor in the decline. I conducted a multistate mark-recapture analysis to estimate juvenile survival in an area of the western population where sea lions are showing signs of recovery. Survival for males and females was 80% between 3 weeks and 1 year of age. Approximately 20% of juveniles continued to be nursed by their mothers between ages 1 and 2 and 10% between ages 2 and 3. Survival for juveniles that suckled beyond 1 year was 88.2% and 89.9% to ages 2 and 3, respectively. In contrast, survival for individuals weaned by age 1 was 40.6% for males and 64.2% for females between ages 1 and 2. Birth mass positively influenced survival for juveniles weaned at age 1 but had little effect on individuals continuing to suckle. Cumulative survival to age 4 was double that estimated during the population decline in this region. Evidence suggests that western Steller sea lions utilize a somewhat different maternal strategy than those in the eastern distinct population. Western adult females generally invest more in their pups during the first year but wean offspring by age 1 more often. This results in better survival to age 1, but greater mortality between ages 1 and 3 compared to the eastern population. Different maternal strategies may reflect density dependent pressures of populations at opposite levels of abundance.
    PLoS ONE 01/2014; 9(5):e96328. · 3.53 Impact Factor
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    ABSTRACT: Steller sea lion (Eumetopias jubatus) numbers in the Western Distinct Population Segment are beginning to recover following the dramatic decline that began in the 1970s and ended around the turn of the century. Low female reproductive rates (natality) may have contributed to the decline and remain an issue of concern for this population. During the 2000s we found high natality among Steller sea lions in the Gulf of Alaska indicating a healthy population. This study extends these previous estimates over an additional three years and tests for interannual variations and long-term trends. We further examine the proportions of pups to adult females observed on the rookery and nearby haulouts during the birthing season to assess whether census data can be used to estimate natality. Open robust design multistate models were built and tested using Program MARK to estimate survival, resighting, and state transition probabilities in addition to other parameters dependent on whether or not a female gave birth in the previous year. Natality was estimated at 70% with some evidence of interannual variation but a long-term increasing or decreasing trend was not supported by the data. Bootstrap and regression comparisons of census data with natality estimates revealed no correlation between the two methods suggesting that census data are not an appropriate proxy for natality in this species. Longitudinal studies of individual animals are an appropriate method for estimating vital rates in species with variable detection over time such as the Steller sea lion. This work indicates that natality remains high in this region and is consistent with a population in recovery. Copyright: ß 2014 Maniscalco et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: The authors confirm that, for approved reasons, some access restrictions apply to the data underlying the findings. All relevant data are within the paper and its Supporting Information files. Funding: This study was funded by U.S. federal grant appropriations through the National Marine Fisheries Service -NOAA Award NA09NMF4390169 (https:// The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist.
    PLoS ONE 11/2014; 9(11):e111523. · 3.53 Impact Factor


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