Population trends of female Elephant Seals breeding on the Courbet Peninsula, îles Kerguelen

Authier, Matthieu; Delord, Karine; Guinet, Christophe

doi:10.1007/s00300-010-0881-1

Cited by 24 publications

(27 citation statements)

References 27 publications

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“…Genetically distinct populations breed principally on mid-latitude islands close to the Antarctic Polar Front (APF), although they may also have occupied higher latitudes during periods of Holocene sea-ice retreat [3]. Following a mid-1800s period of commercial exploitation and subsequent recovery, some major elephant seal populations have exhibited substantial decreases, whereas others have increased or stabilized [4,5]. The drivers responsible for these differing population trajectories remain unresolved, but environmentally mediated food availability at the seals' foraging habitats stands out as the most likely explanation [4].…”

Section: Introductionmentioning

confidence: 99%

Bottom-up regulation of a pole-ward migratory predator population

et al. 2014

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As the effects of regional climate change are most pronounced at polar latitudes, we might expect polar-ward migratory populations to respond as habitat suitability changes. The southern elephant seal (Mirounga leonina L.) is a pole-ward migratory species whose populations have mostly stabilized or increased in the past decade, the one exception being the Macquarie Island population which has decreased continuously over the past 50 years. To explore probable causes of this anomalous trend, we counted breeding female seals annually between 1988 and 2011 in order to relate annual rates of population change (r) to foraging habitat changes that have known connections with atmospheric variability. We found r (i) varied annually from 20.016 to 0.021 over the study period, (ii) was most effected by anomalous atmospheric variability after a 3 year time lag was introduced (R ¼ 0.51) and (iii) was associated with sea-ice duration (SID) within the seals' foraging range at the same temporal lag. Negative r years may be extrapolated to explain, at least partially, the overall trend in seal abundance at Macquarie Island; specifically, increasing SID within the seals foraging range has a negative influence on their abundance at the island. Evidence is accruing that suggests southern elephant seal populations may respond positively to a reduced sea-ice field.

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Section: Introductionmentioning

confidence: 99%

Bottom-up regulation of a pole-ward migratory predator population

et al. 2014

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“… Are seals faithfull to a foraging strategy (Bradshaw et al. 2004)? When do they become faithfull? Are ontogenic shifts in carbon (foraging habitat) and nitrogen (trophic level) isotopes concomitant? Are there notable sex differences? Can we detect differences in stable isotope values before and after the 1970 s population crash (Authier, Delord & Guinet 2011)? …”

Section: Introductionmentioning

confidence: 99%

Breaking the sticks: a hierarchical change‐point model for estimating ontogenetic shifts with stable isotope data

et al. 2011

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Summary1. Stable isotopes are increasingly used in ecology to investigate ontogenetic shifts in foraging habitat (via d 2. In a Bayesian framework, we used a Cholesky decomposition for estimating a moderately-sized covariance matrix, thereby directly estimating correlations between parameters describing time-series of isotopic measurements. We offer guidelines on how to select the covariance structure. 3. The approach is illustrated with a hierarchical change-point (or broken stick) model applied to a data set collected on Southern Elephant Seals, Mirounga leonina. Ontogenetic shifts in foraging habitat, following a juvenile and variable stage, were detected and interpreted as fidelity to a foraging strategy; while ontogenetic shifts in trophic level were more likely the result of complete independence from maternal resources followed by a gradual increase in trophic level as seals aged. 4. Specifying both an appropriate covariance and mean structure enabled us to draw strong inferences on the ecology of an elusive marine predator, and has wide applicability for isotopic ecology provided repeated isotopic measurements are available.

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“…Decimated by sealing in the 1700s and 1800s, populations initially recovered during the early 1900s, only to be followed by a sharp decline in all Indian and Pacific Ocean elephant seal populations between the 1950s and 1990s (McMahon et al 2005a). Time-series data suggest continued decreases in some populations (Macquarie Island;, while others have remained relatively stable (îles Kerguelen; Authier et al 2011) or increased slightly (Marion Island; Pistorius et al 2011) recently. The most plausible hypothesis explaining these declines is a reduction in food resources and/or quality through environmental change (McMahon et al 2005a).…”

Section: Introductionmentioning

confidence: 99%

Decomposing the variance in southern elephant seal weaning mass: partitioning environmental signals and maternal effects

et al. 2015

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Abstract. Predator populations are likely to respond to bottom-up processes, but there remains limited understanding of how wide-ranging marine predators respond to environmentally driven temporal variation in food availability. Widespread declines of several Southern Ocean predators, including southern elephant seals Mirounga leonina, have been attributed to decreases in food availability following environmental changes. We used linear mixed models to examine temporal process variance in weaning mass (a key fitness component) of southern elephant seals at Marion Island over a 27-year period . We quantified the contribution of within-and between-year covariates to the total phenotypic variance in weaning mass and determined whether the observed reversal of population decline was associated with a continued increase in weaning mass, suggesting improvement in per capita food availability to adult females. Weaning mass initially increased rapidly with maternal age, but reached an asymptote when females were nine years old. Longitudinal data examining between-individual maternal differences suggested latent, age-independent maternal influences on weaning mass. Between-year differences accounted for only 6% of the total phenotypic variance in weaning mass. We found no evidence for a systematic trend in weaning mass, but model predicted weaning mass was 8.70 kg (95% CI ¼ 2.14-14.73) lower during the 1980s, suggesting that food limitation may have been most severe during these years when the population was declining. Model support for a population size effect was entirely driven by the low weaning mass and comparatively high (but declining) population size from 1986 to 1988; subsequent variation in population size had no detectable influence on weaning mass. Remotely sensed chlorophyll-a concentration within the seals' foraging distribution explained 45% of the between-year variation (1998-2013, n ¼ 9) in weaning mass, with higher weaning mass in years of positive chlorophyll-a anomalies. Environmental variation associated with variability in the Southern Annular Mode poorly predicted temporal variation in weaning mass. Our long-term data on elephant seal weaning mass provides a perspective on variation in food availability in a pelagic environment which is poorly known. Examining the long-term regionally specific effects of environmental variability aids our understanding of how these predators interact with their environment.

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Population trends of female Elephant Seals breeding on the Courbet Peninsula, îles Kerguelen

Cited by 24 publications

References 27 publications

Bottom-up regulation of a pole-ward migratory predator population

Bottom-up regulation of a pole-ward migratory predator population

Breaking the sticks: a hierarchical change‐point model for estimating ontogenetic shifts with stable isotope data

Decomposing the variance in southern elephant seal weaning mass: partitioning environmental signals and maternal effects

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