The decline of Steller sea lions <i>Eumetopias jubatus</i> in Alaska: a review of the nutritional stress hypothesis

Trites, Andrew W.; Donnelly, Carolyn P.

doi:10.1046/j.1365-2907.2003.00009.x

Cited by 304 publications

(299 citation statements)

References 85 publications

(135 reference statements)

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“…Competition between sea lions and commercial fisheries may occur around the Auckland Islands (Meynier et al 2010) as reported for other large marine carni-vores interacting with fisheries (Alonzo et al 2003, Trites & Donnelly 2003, Drago et al 2009). However, the management of the Auckland Islands populations of New Zealand sea lions currently focuses on reducing the bycatch rate in squid fisheries but does not take into consideration the impact of resource competition with fisheries (Chilvers 2008).…”

Section: Fishing Competition: Impact On the Differences Observed And mentioning

confidence: 70%

Foraging behaviour indicates marginal marine habitat for New Zealand sea lions: remnant versus recolonising populations

Augé¹,

Chilvers²,

Moore³

et al. 2011

Mar. Ecol. Prog. Ser.

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The New Zealand sea lion Phocarctos hookeri historically bred on the New Zealand mainland (South and North Islands). Subsistence hunting and later commercial sealing reduced its distribution to 3 breeding areas at the spatial edges of its historical distribution range, in the Auckland Islands (AI) and on Campbell Island. Here, we present foraging areas and foraging trips of female New Zealand sea lions from the Otago Peninsula, where a recolonising population has been found in the core of the historical range of the species. We compare the results with data from the AI in order to assess the theory that the spatial margin of a species' distribution represents the lower end of habitat suitability. Female New Zealand sea lions at Otago had significantly smaller foraging ranges than females at the AI (mean 65% Kernel ranges: 47 ± 25 km 2 versus 687 ± 109 km 2 ), made shorter foraging trips (mean 11.8 ± 2.3 h versus 66.2 ± 4.2 h), and spent 40% less time at sea overall. Juvenile females at Otago from age 2 onwards could access foraging grounds used by adult females nursing pups; this is unlikely to be the case at the AI due to the large distances and associated depths of foraging grounds. Our study illustrates the theory that spatial marginality is related to habitat marginality. Existing management measures to mitigate the impact of bycatch in fisheries on declining remnant colonies around the AI were modelled based on populations exploiting optimal habitat. They should now integrate this new information.

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Section: Fishing Competition: Impact On the Differences Observed And mentioning

confidence: 70%

Foraging behaviour indicates marginal marine habitat for New Zealand sea lions: remnant versus recolonising populations

Augé¹,

Chilvers²,

Moore³

et al. 2011

Mar. Ecol. Prog. Ser.

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“…Thus there is potential to physiologically assess the probability of achieving viable weaning mass for each pup, during pregnancy, on the basis of maternal nutritional state (Trites & Donnelly 2003). Evidence suggests that when foraging conditions are challenging, some species tend to terminate pregnancy and thereby conserve energy, as opposed to proceeding with reproduction and depleting body stores when there is minimal chance of producing a viable pup (Boyd 2000).…”

Section: Life History Strategymentioning

confidence: 99%

Annual reproductive rates of Weddell seals in eastern Antarctica from 1973 to 2000

Lake

Burton²,

Barker³

et al. 2008

Mar. Ecol. Prog. Ser.

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This study is based on mark and re-sight observations of Weddell seals Leptonychotes weddelli at the Vestfold Hills (68°S, 78°E), which form a considerable time series (1973 to 2000) pertaining to Prydz Bay in eastern Antarctica. We use multi-strata modeling to estimate annual rates of reproduction and survival whilst taking into account annual and breeding state-specific re-sight probability. Inter-annual variation in both the proportion of females producing pups and the proportion of pups surviving juvenile years reveals the indefinite outcome of each reproductive opportunity for this species of the high Antarctic. In contrast, the relatively high and stable survival rates of breeding females lead to long life span and a spreading-out of reproductive bouts so that individuals sample a number of environments and, given environmental uncertainty, increase the probability of reproducing in a good season when pups are more likely to survive. Lack of evidence for costs of reproduction suggests that Weddell seals prudently select years for reproduction to conserve energy by pre-empting unsuccessful attempts. We propose terminating pregnancy is the Weddell seal's primary physiological mechanism to endure and buffer fluctuations in the environment. The time-series of reproductive rates signals ecosystem change. From 1973 to 2000, annual reproductive rates ranged from 53 to 88%. More recent (1990s) low reproductive rates were not linked to El Niño Southern Oscillation (ENSO) events compared to earlier decades.KEY WORDS: Weddell seal · Ecosystem monitoring · Antarctic · Reproductive rate · Mark and re-sight · MARK Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 366: [259][260][261][262][263][264][265][266][267][268][269][270] 2008 forsteri at Terre Adélie (66°30' S, 141°01' E) (Woehler et al. 2002). Monitoring single-predator populations has potential to show changes over time in demographic rates, which are in themselves quantitative measures of population status. As part of a suite of parameters from various populations, the same time series may provide 'snap-shots' of the state of the environment. Ultimately, simultaneous interpretation of multiple time series could provide a basis for ecosystem models (Constable et al. 2003).This approach to ecosystem monitoring is conceptually focused on the predator's 'perspective' of the environment (Fraser & Hofmann 2003). Nevertheless, there are many examples where Antarctic predator time series are congruent with large scale physical phenomena (e.g. Whitehead et al. 1990, Testa et al. 1991, Fraser & Hofmann 2003, Jenouvrier et al. 2003, 2005. In the Southern Hemisphere, it is common for signals of reduced productivity to coincide with El Niño events (Trillmich & Ono 1991). One of the first studies to propose such a link cited a reproduction time series from Weddell seals in McMurdo Sound (Testa et al. 1991). A decade later, scientists documented ENSO forcing of physical parameters in the Southern Ocean (Kwok & Comis...

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“…Similarly, the role of different age-classes and demographic parameters in the decline likely shifted over time (York 1994, Holmes and York 2003, Pendleton et al 2006, Winship and Trites 2006. The current apparent stability of the western population in the Gulf of Alaska at a much reduced level (Eberhardt et al 2005, Winship and Trites 2006, Boyd 2010) may now depend upon maintaining high adult survival ) and may reflect a new carrying capacity (Trites and Donnelly 2003).…”

Section: Introductionmentioning

confidence: 99%

Cohort effects and spatial variation in age-specific survival of Steller sea lions from southeastern Alaska

et al. 2011

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Pitcher. 2011. Cohort effects and spatial variation in age-specific survival of Steller sea lions from southeastern Alaska.Ecosphere 2(10):111. doi:10.1890/ES11-00215.1Abstract. Information concerning mechanistic processes underlying changes in vital rates and ultimately population growth rate is required to monitor impacts of environmental change on wildlife. We estimated age-specific survival and examined factors influencing survival for a threatened population of Steller sea lions (Eumetopias jubatus) in southeastern Alaska. We used mark-recapture models and data from 1,995 individuals marked at approximately one month of age at four of five rookeries in southeastern Alaska, and resighted from Oregon to the Bering Sea. Average annual survival probability for females was 0.64 for pups and 0.77 for yearlings, and increased from 0.91 to 0.96 from age 3-7 yrs. Annual survival probability of males averaged 0.60 for pups and 0.88 by 7 yrs, resulting in probability of survival to age 7, 33% lower for males compared to females. Pups from northern southeastern Alaska (including an area of low summer population size but rapid growth) were twice as likely to survive to age 7 compared to pups from southern rookeries (including a large, historical, stable rookery). Effects of early conditions on future fitness were observed as (1) environmental conditions in the birth year equally affected first-and secondyear survival, and (2) effects of body mass at approximately one month of age were still apparent at 7 yrs. Survival from 0-2 yrs varied among five cohorts by a maximum absolute difference of 0.12. We observed survival costs for long-distance dispersal for males, particularly as juveniles. However, survival was higher for non-pups that dispersed to northern southeastern Alaska, suggesting that moving to an area with greater productivity, greater safety, or lower population size may alleviate a poor start and provide a mechanism for spatial structure for sea lion populations.

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The decline of Steller sea lions Eumetopias jubatus in Alaska: a review of the nutritional stress hypothesis

Cited by 304 publications

References 85 publications

Foraging behaviour indicates marginal marine habitat for New Zealand sea lions: remnant versus recolonising populations

Foraging behaviour indicates marginal marine habitat for New Zealand sea lions: remnant versus recolonising populations

Annual reproductive rates of Weddell seals in eastern Antarctica from 1973 to 2000

Cohort effects and spatial variation in age-specific survival of Steller sea lions from southeastern Alaska

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