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Abstract The krill surplus hypothesis of unlimited prey resources available for Antarctic predators due to commercial whaling in the 20th century has remained largely untested since the 1970s. Rapid warming of the Western Antarctic Peninsula (WAP) over the past 50 years has resulted in decreased seasonal ice cover and a reduction of krill. The latter is being exacerbated by a commercial krill fishery in the region. Despite this, humpback whale populations have increased but may be at a threshold for growth based on these human‐induced changes. Understanding how climate‐mediated variation in prey availability influences humpback whale population dynamics is critical for focused management and conservation actions. Using an 8‐year dataset (2013–2020), we show that inter‐annual humpback whale pregnancy rates, as determined from skin‐blubber biopsy samples (n = 616), are positively correlated with krill availability and fluctuations in ice cover in the previous year. Pregnancy rates showed significant inter‐annual variability, between 29% and 86%. Our results indicate that krill availability is in fact limiting and affecting reproductive rates, in contrast to the krill surplus hypothesis. This suggests that this population of humpback whales may be at a threshold for population growth due to prey limitations. As a result, continued warming and increased fishing along the WAP, which continue to reduce krill stocks, will likely impact this humpback whale population and other krill predators in the region. Humpback whales are sentinel species of ecosystem health, and changes in pregnancy rates can provide quantifiable signals of the impact of environmental change at the population level. Our findings must be considered paramount in developing new and more restrictive conservation and management plans for the Antarctic marine ecosystem and minimizing the negative impacts of human activities in the region.
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This content will become publicly available on October 16, 2026
Environmental influences on population-level reproductive output of Weddell seals Leptonychotes weddellii in the Ross Sea, Antarctica
The Ross Sea in the Southern Ocean is frequently considered one of the most pristine ecosystems in the world, but recent data suggest that changes to oceanic conditions may be impacting wildlife abundance. We used 41 yr of data to assess how variation in biologically relevant environmental conditions relates to annual reproductive output for the world’s largest population of Weddell sealsLeptonychotes weddellii, an upper-level predator in the Ross Sea. Pup production increased 150% across the time series, and interannual variation tripled. Linear regression analyses, which explained 73.7% of the variance in pup production, supported a non-linear, convex relationship between reproductive output and summer sea ice extent, with more pups born in years with more or less sea ice than in years with intermediate ice extent. While total annual toothfish catch 7 yr previous appears to be positively associated with reproductive output, a similar amount of variation in pup production could be explained by an alternative model with a linear, temporal trend. Our results highlight a sizable increase in the reproductive output of this demographically buffered polar marine predator. The increase in pup production may be the result of competitive release due to commercial fishing, cascading ecological effects from commercial fishing or other environmental shifts, or population inertia from a few large birth cohorts. It is challenging to disentangle these hypotheses with the current publicly available environmental data. Future demographic analyses and collaborative research are needed to understand how environmental changes are impacting marine populations in this ecosystem.
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- PAR ID:
- 10651748
- Publisher / Repository:
- Inter-Research Science Publisher
- Date Published:
- Journal Name:
- Marine Ecology Progress Series
- Volume:
- 771
- ISSN:
- 0171-8630
- Page Range / eLocation ID:
- 139 to 154
- Subject(s) / Keyword(s):
- Pinniped Population dynamics Pup production Sea ice Southern Ocean Long-term data series
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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