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: ABSTRACT  Steller sea lion (Eumetopias jubatus) pups (n = 366) were hot-branded at Lowrie Island, Southeast Alaska, USA, in June 2001 and 2002 for vital-rates studies. To assess potential mortality following branding, we estimated weekly survival to 12 weeks postbranding using mark-recapture models. Survival estimates ranged from 0.984/week to 0.988/week, or 0.868 over the 12-week period; varied little with sex, year, and capture area; and were higher for larger than smaller male pups and unexpectedly lower for larger than smaller female pups. Inclusion of resights at 1–3 years of age prevented a −4.5% bias in cumulative survival to 12 weeks postbranding by accounting for pups that survived but permanently emigrated from Lowrie Island during the 12-week survey. Data from double-marked pups (i.e., branded and flipper-tagged) indicated the low brand-misreading probability of 3.1% did not bias survival estimates. Assuming survival differences between the first 2 weeks postbranding and later weeks were due entirely to the branding event, potential postbranding mortality of branded pups attributable to the branding event was 0.5–0.7%, or one pup for every 200 marked. Weekly survival of branded pups was nearly identical to estimates from a control group of undisturbed, unbranded pups born to 10–11-year-old branded adult females in 2005 (0.987–0.988/week) and similar to pup survival estimates from other otariid studies. Available data did not indicate substantial mortality to 12 weeks postbranding resulting from the branding disturbance, suggesting branding of Steller sea lion pups can be used effectively for investigations of population declines without significantly affecting population health or study goals.
    Journal of Wildlife Management 12/2010; 73(7):1040 - 1051. · 1.64 Impact Factor
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    ABSTRACT: Maternal attendance patterns in free-ranging wildlife can provide insight into basic biology, foraging behavior, and population dynamics. We collected detailed visual observations of attendance patterns by adult lactating Steller sea lions (Eumetopias jubatus) from 2005 to 2007 on 6 major rookeries in the Russian Far East, including those with an increasing population trend (Sea of Okhotsk), severely depleted populations that were recovering (Kuril Islands), or those that were stable (Commander Islands). Individually identifiable females were observed during the postpartum period, with special attention paid to presence and absence during the day and to departure and arrival times. Within Russia females on several Kuril Islands rookeries exhibited extremely short foraging trip durations (median 6.5–8.0 h) and spent higher proportions of time on the rookery (75–82%), whereas females in the Sea of Okhotsk population had the longest trips (median 19.8 h) and spent the least amount of time on the rookery (60%). Most indices of attendance pattern were more favorable (longer peripartum period, higher proportion of time spent on rookery, shorter trips, and longer visits) than those reported in Alaska and much more so than those in California during El Niño years, where the proportion of time spent on the rookery was nearly half that in Russia. Females >6 years of age had shorter trips and longer visit durations than the youngest females (4–5 years), and older mothers exhibited significantly longer periods of nursing before taking their 1st trip, suggesting greater physical condition for older females. Although trip durations remained constant throughout the season, visit durations shortened significantly as the pups aged, suggesting that increasing nutritional demands of pups are met by more frequent, rather than longer, trips. No apparent relationships between attendance patterns and population status were observed; however, many of the differences in attendance patterns throughout the range of the Steller sea lion could be related to local variation in bathymetry and diet patterns.
    Journal of Mammalogy 04/2011; · 2.31 Impact Factor


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