Population dynamics of southern elephant seals: a synthesis of three decades of demographic research at Marion Island

Pistorius, Pierre A.; Bruyn, P. J. Nico de; Bester, M.N.

doi:10.2989/1814232x.2011.637357

Cited by 45 publications

(56 citation statements)

References 127 publications

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“…Almost all weaned pups born on MI since 1983 were double tagged in each of their hind flippers with a uniquely numbered, colour-coded Dalton Jumbo® tag (Pistorius et al 2011). Since 1983, southern elephant seals were checked for the presence of tags on all popular beaches along the coastline (Fig.…”

Section: Mark-recapture Programmentioning

confidence: 99%

“…Age compositions of harems at Marion Island usually include a small number of 3 year old females, which could be due to the majority of this female age class gaining insufficient mass to breed (Pistorius et al 2011). Three year old female arrival mass differed significantly (t (-5.27) , df =3.34, P = 0.01, Table 2) from 4 year old females.…”

Section: Restraint Hypothesis Testingmentioning

confidence: 99%

“…The extensive mark-recapture schedule (de Bruyn et al 2012) that assessed pup survival for 2-4 years depending on date of birth (by which some are already adults) attributes to high recapture rates (Pistorius et al 2011). The likelihood of missing an individual in consecutive haulouts if individual is present is small, as haulouts (winter and moult) for this age class last up to a month, which can include 3 census occasions.…”

Section: Offspring Survivalmentioning

confidence: 99%

“…Pistorius et al 2001;de Bruyn et al 2011) and our present photogrammetric results enlightened us to different southern elephant seal breeding strategies that might be at work at Marion Island. Firstly, age composition of harems include a relatively smaller number of 3 year old, than 4 year old females which could be due to the majority of this female age class gaining insufficient mass to breed (Pistorius et al 2011). Three year old female arrival mass significantly differed from that of 4 year old females (present study), corroborating assertions by Pistorius et al (2011).…”

Section: Hypotheses Accounting For Age Related Reproduction Improvementmentioning

confidence: 99%

“…Firstly, age composition of harems include a relatively smaller number of 3 year old, than 4 year old females which could be due to the majority of this female age class gaining insufficient mass to breed (Pistorius et al 2011). Three year old female arrival mass significantly differed from that of 4 year old females (present study), corroborating assertions by Pistorius et al (2011). Weaning mass of pups from 3 year old females (mean = 81.67 ± 7.76 kg) compared to pups from 4 year old mothers (mean = 117.40 ± 24.14 kg) differ greatly and supports the hypothesis that the main contributor to pup mass is female age and size.…”

Section: Hypotheses Accounting For Age Related Reproduction Improvementmentioning

confidence: 99%

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Age-related reproductive variation in a wild marine mammal population

2013

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Life history theory predicts a change in reproduction success with age as energy resources are limited and must be allocated effectively to maximise reproduction and survival. In this study we use three reproductive performance measures; maternal expenditure, offspring weaning mass and first year survival to investigate the role maternal age plays in successful reproduction. Long-term uninterrupted life history data available for Marion Island's southern elephant seals and mass change estimates from photogrammetry data allow for assessment of age related reproduction performance and trade-offs. Known-aged adult females were photographed for photogrammetric mass estimation (n=29) and their pups weighed at weaning during the 2009 breeding season. Maternal age and proportional mass loss positively influenced pup weaning mass. In turn first year pup return rates (as a proxy for survival) were assessed through the intensive mark-recapture program.Pup survival increased with female age and weaning mass. Pups of young females aged 3 to 6 years have a lower 1 st year survival probability compared to pups of older and larger females.

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Section: Mark-recapture Programmentioning

confidence: 99%

Section: Restraint Hypothesis Testingmentioning

confidence: 99%

Section: Offspring Survivalmentioning

confidence: 99%

Section: Hypotheses Accounting For Age Related Reproduction Improvementmentioning

confidence: 99%

Section: Hypotheses Accounting For Age Related Reproduction Improvementmentioning

confidence: 99%

See 3 more Smart Citations

Age-related reproductive variation in a wild marine mammal population

2013

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Individual heterogeneity in life‐history trade‐offs with age at first reproduction in capital breeding elephant seals

et al. 2019

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Recruitment age plays a key role in life‐history evolution. Because individuals allocate limited resources among competing life‐history functions, theory predicts trade‐offs between current reproduction and future growth, survival and/or reproduction. Reproductive costs tend to vary with recruitment age, but may also be overridden by fixed individual differences leading to persistent demographic heterogeneity and positive covariation among demographic traits at the population level. We tested for evidence of intra‐ and inter‐generational trade‐offs and individual heterogeneity relating to age at first reproduction using three decades of detailed individual life‐history data of 6,439 capital breeding female southern elephant seals. Contrary to the predictions from trade‐off hypotheses, we found that recruitment at an early age was associated with higher population level survival and subsequent breeding probabilities. Nonetheless, a survival cost of first reproduction was evident at the population level, as first‐time breeders always had lower survival probabilities than prebreeders and experienced breeders of the same age. However, models accounting for hidden persistent demographic heterogeneity revealed that the trade‐off between first reproduction and survival was only expressed in “low quality” individuals, comprising 35% of the population. The short‐term somatic costs associated with breeding at an early age had no effect on the ability of females to allocate resources to offspring in the next breeding season. Our results provide strong evidence for individual heterogeneity in the life‐history trajectories of female elephant seals. By explicitly modeling hidden persistent demographic heterogeneity we show that individual heterogeneity governs the expression of trade‐offs with first reproduction in elephant seals.

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The effect of prey abundance and fisheries on the survival, reproduction, and social structure of killer whales (Orcinus orca) at subantarctic Marion Island

Jordaan

Oosthuizen

Reisinger

et al. 2023

Ecology and Evolution

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Most marine apex predators are keystone species that fundamentally influence their ecosystems through cascading top-down processes. Reductions in worldwide predator abundances, attributed to environmental-and anthropogenic-induced changes to prey availability and negative interactions with fisheries, can have far-reaching ecosystem impacts. We tested whether the survival of killer whales (Orcinus orca) observed at Marion Island in the Southern Indian Ocean correlated with social structure and prey variables (direct measures of prey abundance, Patagonian toothfish fishery effort, and environmental proxies) using multistate models of capture-recapture data spanning 12 years (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018). We also tested the effect of these same variables on killer whale social structure and reproduction measured over the same period. Indices of social structure had the strongest correlation with survival, with higher sociality associated with increased survival probability. Survival was also positively correlated with Patagonian toothfish fishing effort during the previous year, suggesting that fishery-linked resource availability is an important determinant of survival. No correlation between survival and environmental proxies of prey abundance was found. Atisland prey availability influenced the social structure of Marion Island killer whales, but none of the variables explained variability in reproduction. Future increases in legal fishing activity may benefit this population of killer whales through the artificial provisioning of resources they provide.

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Population dynamics of southern elephant seals: a synthesis of three decades of demographic research at Marion Island

Cited by 45 publications

References 127 publications

Age-related reproductive variation in a wild marine mammal population

Age-related reproductive variation in a wild marine mammal population

Individual heterogeneity in life‐history trade‐offs with age at first reproduction in capital breeding elephant seals

The effect of prey abundance and fisheries on the survival, reproduction, and social structure of killer whales (Orcinus orca) at subantarctic Marion Island

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