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

Hoff, John van den; McMahon, Clive R.; Simpkins, Graham; Hindell, Mark A.; Alderman, Rachael; Burton, Harry R.

doi:10.1098/rspb.2013.2842

Cited by 33 publications

(43 citation statements)

References 68 publications

(144 reference statements)

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“…A growing body of evidence, including this study, links changes in sea ice distribution and dynamics with the decrease in seal numbers at Macquarie Island Van den Hoff et al, 2014). This decrease stands in contrast to all other southern elephant seal populations that are either stable or increasing .…”

Section: Discussionmentioning

confidence: 66%

“…Southern elephant seal populations occur in four genetically distinct stocks (Corrigan, Fabiani, & Chauke, 2016;Slade, Moritz, Hoelzel, & Burton, 1998). The proximate mechanism of how food availability affects population growth is still unclear but recruitment into the population is lower when sea ice duration is greatest (Van den Hoff et al, 2014). However, the Macquarie Island population (which contains more than 90% of the overall Macquarie stock in the southern Pacific) is decreasing, and has been doing so for several decades Van den Hoff et al, 2014).…”

Section: Our Knowledge Of the Basic Biology And Distribution Of Southernmentioning

confidence: 99%

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Decadal changes in habitat characteristics influence population trajectories of southern elephant seals

Hindell

Sumner

Bestley

et al. 2017

Global Change Biology

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Understanding divergent biological responses to climate change is important for predicting ecosystem level consequences. We use species habitat models to predict the winter foraging habitats of female southern elephant seals and investigate how changes in environmental variables within these habitats may be related to observed decreases in the Macquarie Island population. There were three main groups of seals that specialized in different ocean realms (the sub-Antarctic, the Ross Sea and the Victoria Land Coast). The physical and climate attributes (e.g. wind strength, sea surface height, ocean current strength) varied amongst the realms and also displayed different temporal trends over the last two to four decades. Most notably, sea ice extent increased on average in the Victoria Land realm while it decreased overall in the Ross Sea realm. Using a species distribution model relating mean residence times (time spent in each 50 × 50 km grid cell) to 9 climate and physical co-variates, we developed spatial predictions of residence time to identify the core regions used by the seals across the Southern Ocean from 120°E to 120°W. Population size at Macquarie Island was negatively correlated with ice concentration within the core habitat of seals using the Victoria Land Coast and the Ross Sea. Sea ice extent and concentration is predicted to continue to change in the Southern Ocean, having unknown consequences for the biota of the region. The proportion of Macquarie Island females (40%) utilizing the relatively stable sub-Antarctic region, may buffer this population against longer-term regional changes in habitat quality, but the Macquarie Island population has persistently decreased (-1.45% per annum) over seven decades indicating that environmental changes in the Antarctic are acting on the remaining 60% of the population to impose a long-term population decline in a top Southern Ocean predator.

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Section: Discussionmentioning

confidence: 66%

Section: Our Knowledge Of the Basic Biology And Distribution Of Southernmentioning

confidence: 99%

Decadal changes in habitat characteristics influence population trajectories of southern elephant seals

Hindell

Sumner

Bestley

et al. 2017

Global Change Biology

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“…While the major populations at Iles Kerguelen and Heard Island, Peninsula Valdes and South Georgia have stabilized or increased [9], the Macquarie Island population in the southern Pacific Ocean has declined continuously at a mean rate of 0.8% per annum since the 1950s [10]. Although the cause of this decline remains unknown, it is thought to be due to changing oceanic conditions leading to reductions in the foraging success of Macquarie Island breeding females through alterations in the availability or quality of their prey.…”

Section: Introductionmentioning

confidence: 99%

Five decades on: Use of historical weaning size data reveals that a decrease in maternal foraging success underpins the long-term decline in population of southern elephant seals (Mirounga leonina)

2017

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The population of Southern elephant seals (Mirounga leonina) at Macquarie Island has declined since the 1960s, and is thought to be due to changing oceanic conditions leading to reductions in the foraging success of Macquarie Island breeding females. To test this hypothesis, we used a 55-year-old data set on weaning size of southern elephant seals to quantify a decrease in weaning size from a period of population stability in 1950s to its present state of on-going decline. Being capital breeders, the size of elephant seal pups at weaning is a direct consequence of maternal foraging success in the preceding year. During the 1940-1950s, the mean of female pups at weaning was similar between the Heard and Macquarie Island populations, while the snout-tail-length length of male weaners from Heard Island were longer than their conspecifics at Macquarie Island. Additionally, the snout-tail-length of pups at weaning decreased by 3cm between the 1950s and 1990s in the Macquarie Island population, concurrent with the observed population decline. Given the importance of weaning size in determining first-year survival and recruitment rates, the decline in the size at weaning suggests that the decline in the Macquarie Island population has, to some extent, been driven by reduced maternal foraging success, consequent declines in the size of pups at weaning, leading to reduced first-year survival rates and recruitment of breeding females into the population 3 to 4 years later.

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“…Despite the long-term decline in the Macquarie Island population [22], our study shows that a mechanism for safely reducing the age of primiparity does not seem to exist. Instead, we found that the cost of first reproduction at age three remained very high.…”

Section: Discussionmentioning

confidence: 94%

Age-specific cost of first reproduction in female southern elephant seals

et al. 2014

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When to commence breeding is a crucial life-history decision that may be the most important determinant of an individual's lifetime reproductive output and can have major consequences on population dynamics. The age at which individuals first reproduce is an important factor influencing the intensity of potential costs (e.g. reduced survival) involved in the first breeding event. However, quantifying age-related variation in the cost of first reproduction in wild animals remains challenging because of the difficulty in reliably recording the first breeding event. Here, using a multi-event capture-recapture model that accounts for both imperfect detection and uncertainty in the breeding status on an 18-year dataset involving 6637 individuals, we estimated age and state-specific survival of female elephant seals (Mirounga leonina) in the declining Macquarie Island population. We detected a clear cost of first reproduction on survival. This cost was higher for both younger first-time breeders and older first-time breeders compared with females recruiting at age four, the overall mean age at first reproduction. Neither earlier primiparity nor delaying primiparity appear to confer any evolutionary advantage, rather the optimal strategy seems to be to start breeding at a single age, 4 years.

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

Cited by 33 publications

References 68 publications

Decadal changes in habitat characteristics influence population trajectories of southern elephant seals

Decadal changes in habitat characteristics influence population trajectories of southern elephant seals

Five decades on: Use of historical weaning size data reveals that a decrease in maternal foraging success underpins the long-term decline in population of southern elephant seals (Mirounga leonina)

Age-specific cost of first reproduction in female southern elephant seals

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