Environmental correlates of temporal variation in the prey species of Australian fur seals inferred from scat analysis

Kliska, Kimberley; McIntosh, Rebecca R.; Jonsen, Ian D.; Hume, Fiona; Dann, Peter; Kirkwood, Roger; Harcourt, Robert

doi:10.1098/rsos.211723

Cited by 7 publications

(7 citation statements)

References 75 publications

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“…Australian fur seals are broadly understood to be an opportunistic predator with diet plasticity. Supporting this, the diet at Seal Rocks has changed since 1997 in response to large-scale climate and oceanographic processes [25,78,79]. Climate change is predicted to affect ocean temperature, currents and upwelling periods that will alter food webs [80] and eastern Bass Strait is a hotspot of global warming [5].…”

Section: Plos Onementioning

confidence: 99%

“…Australian fur seal populations have experienced rapid change over the last 200 years and currently show detectable responses to ecosystem change in their diet, movement, health, and population size [15,[25][26][27]. Sealing gangs were active in Bass Strait in the late 1700s and by 1830, had driven Australian seal species almost to extinction in just 40 years [28,29] (Fig 2 ; S1 Table in S1 File).…”

Section: Introductionmentioning

confidence: 99%

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Sustained reduction in numbers of Australian fur seal pups: Implications for future population monitoring

McIntosh

Sorrell

Thalmann³

et al. 2022

PLoS ONE

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Fur seal populations in the Southern Hemisphere were plundered in the late 1700s and early 1800s to provide fur for a clothing industry. Millions of seals were killed resulting in potentially major ecosystem changes across the Southern Hemisphere, the consequences of which are unknown today. Following more than a century of population suppression, partly through on-going harvesting, many of the fur seal populations started to recover in the late 1900s. Australian fur seals (Arctocephalus pusillus doriferus), one of the most geographically constrained fur seal species, followed this trend. From the 1940s to 1986, pup production remained at approximately 10,000 per year, then significant growth commenced. By 2007, live pup abundance had recovered to approximately 21,400 per year and recovery was expected to continue However, a species-wide survey in 2013 recorded a 20% decline, to approximately 16,500 live pups. It was not known if this decline was due to 2013 being a poor breeding year or a true population reduction. Here we report the results of a population-wide survey conducted in 2017 and annual monitoring at the most productive colony, Seal Rocks, Victoria that recorded a large decline in live pup abundance (-28%). Sustained lower pup numbers at Seal Rocks from annual counts between 2012–2017 (mean = 2908 ± 372 SD), as well as the population-wide estimate of 16,903 live pups in 2017, suggest that the pup numbers for the total population have remained at the lower level observed in 2013 and that the 5-yearly census results are not anomalies or representative of poor breeding seasons. Potential reasons for the decline, which did not occur range-wide but predominantly in the most populated and long-standing breeding sites, are discussed. To enhance adaptive management of this species, methods for future monitoring of the population are also presented. Australian fur seals occupy several distinct regions influenced by different currents and upwellings: range-wide pup abundance monitoring enables comparisons of ecosystem status across these regions. Forces driving change in Australian fur seal pup numbers are likely to play across other marine ecosystems, particularly in the Southern Hemisphere where most fur seals live.

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Section: Plos Onementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sustained reduction in numbers of Australian fur seal pups: Implications for future population monitoring

McIntosh

Sorrell

Thalmann³

et al. 2022

PLoS ONE

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“…Their populations at the margins remain small and predominantly consists of juveniles and sub-adult males (Burleigh et al 2008 ), though both breed on Montague Island (36° 14′ S, 150° 13′ E), in small numbers (McIntosh et al 2018 ). The two species are typically considered ‘generalists’ due to their broad diets (Page et al 2005a ; Kliska et al 2022 ), but in some areas, Australian fur seals do exhibit individual specialisations in diet and foraging (Kernaléguen et al 2012 , 2016 ; Knox et al 2018 ). The two species have apparently distinct foraging modes, with Australian fur seals primarily foraging during benthic dives over the continental shelf (Knox et al 2017 ; Salton et al 2019 ) and New Zealand fur seals foraging during pelagic dives on and off the continental shelf (Page et al 2005b , 2006 ; Salton et al 2021 ).…”

Section: Introductionmentioning

confidence: 99%

Niche partitioning and individual specialisation in resources and space use of sympatric fur seals at their range margin

Salton,

Raoult,

Jonsen

et al. 2024

Oecologia

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Ecological theory predicts niche partitioning between high-level predators living in sympatry as a mechanism to minimise the selective pressure of competition. Accordingly, male Australian fur seals Arctocephalus pusillus doriferus and New Zealand fur seals A. forsteri that live in sympatry should exhibit partitioning in their broad niches (in habitat and trophic dimensions) in order to coexist. However, at the northern end of their distributions in Australia, both are recolonising their historic range after a long absence due to over-exploitation, and their small population sizes suggest competition should be weak and may allow overlap in niche space. We found some niche overlap, yet clear partitioning in diet trophic level (δ15N values from vibrissae), spatial niche space (horizontal and vertical telemetry data) and circadian activity patterns (timing of dives) between males of each species, suggesting competition may remain an active driver of niche partitioning amongst individuals even in small, peripheral populations. Consistent with individual specialisation theory, broad niches of populations were associated with high levels of individual specialisation for both species, despite putative low competition. Specialists in isotopic space were not necessarily specialists in spatial niche space, further emphasising their diverse individual strategies for niche partitioning. Males of each species displayed distinct foraging modes, with Australian fur seals primarily benthic and New Zealand fur seals primarily epipelagic, though unexpectedly high individual specialisation for New Zealand fur seals might suggest marginal populations provide exceptions to the pattern generally observed amongst other fur seals.

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“…The broad-scale environmental indices of the Indian Ocean Dipole (IOD) (Saji et al, 1999), the Southern Annular Mode (SAM) (Lovenduski and Gruber, 2005) and the Southern Oscillation Index (SOI) (Middleton et al, 2007) have been observed to influence the marine ecosystem of south-eastern Australia, including the foraging and reproductive ecologies of locally breeding predators (Bunce et al, 2002;Kliska, 2016;Speakman et al, 2021;Geeson et al, 2022). Correspondingly, relationships between the annual means of these indices and BCI were investigated.…”

Section: Environmental Variablesmentioning

confidence: 99%

“…While environmental influences on Australian fur seal foraging behaviour, habitat use and diet have previously been documented (Speakman et al, 2020;Speakman et al, 2021;Geeson et al, 2022;Kliska et al, 2022;McIntosh et al, 2022), little is known of factors impacting body condition over the long term in the species (Arnould and Warneke, 2002;Wall et al, 2023). Such information is crucial for predicting how the species, and the ecosystem they dominate, may respond to future environmental change.…”

Section: Introductionmentioning

confidence: 99%

Long-term decline in body condition of female Australian fur seals: potential causes and implications

Geeson,

Hindell,

Hobday

et al. 2023

Front. Mar. Sci.

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The Australian fur seal (Arctocephalus pusillus doriferus, AUFS) population is still recovering from the over-exploitation of the commercial-sealing era (18th and 19th centuries). While the population is considered to be only < 47% of its pre-harvest size, it now represents the greatest resident marine predator biomass in the south-eastern Australian marine ecosystem. The region is experiencing rapid environmental change and, as a keystone predator species, the AUFS is an indicator of ecosystem health. In the present study, the body mass, standard length and body condition index (BCI) were analysed between 1997-2021 in adult female AUFS provisioning pups on Kanowna Island (northern Bass Strait), the third largest colony for the species. While substantial inter-annual fluctuations were observed, there was no temporal trend in standard length during the 23-year study period. In contrast, body mass and, consequently, BCI decreased significantly, suggesting the population is experiencing changing nutritional conditions. While these changes do not appear to be due to competition with commercial fisheries or population expansion, weak but significant negative relationships were observed between BCI and 1-year lagged sea surface temperature and summer zonal winds in the Bonney Upwelling region, and both current- and 2-year lagged Indian Ocean Dipole (IOD). These findings suggest the BCI of AUFS may continue to decline under predicted climate change conditions. While a lack of a concurrent decline in pup production could indicate a degree of nutritional tolerance or flexibility in energy allocation, further monitoring is required to assess decreases in reproductive parameters (e.g., birth mass, pre-weaning growth rates) or vital rates, which would be expected with continued nutritional stress.

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Environmental correlates of temporal variation in the prey species of Australian fur seals inferred from scat analysis

Cited by 7 publications

References 75 publications

Sustained reduction in numbers of Australian fur seal pups: Implications for future population monitoring

Sustained reduction in numbers of Australian fur seal pups: Implications for future population monitoring

Niche partitioning and individual specialisation in resources and space use of sympatric fur seals at their range margin

Long-term decline in body condition of female Australian fur seals: potential causes and implications

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