Abstract
Antarctic fur seals (AFS) are an ecologically important predator and a focal indicator species for ecosystem-based Antarctic fisheries management. This species suffered intensive anthropogenic exploitation until the early 1900s, but recolonized most of its former distribution, including the southern-most colony at Cape Shirreff, South Shetland Islands (SSI). The IUCN describes a single, global AFS population of least concern; however, extensive genetic analyses clearly identify four distinct breeding stocks, including one in the SSI. To update the population status of SSI AFS, we analyzed 20 years of field-based data including population counts, body size and condition, natality, recruitment, foraging behaviors, return rates, and pup mortality at the largest SSI colony. Our findings show a precipitous decline in AFS abundance (86% decrease since 2007), likely driven by leopard seal predation (increasing since 2001, p << 0.001) and potentially worsening summer foraging conditions. We estimated that leopard seals consumed an average of 69.3% (range: 50.3–80.9%) of all AFS pups born each year since 2010. AFS foraging-trip durations, an index of their foraging habitat quality, were consistent with decreasing krill and fish availability. Significant improvement in the age-specific over-winter body condition of AFS indicates that observed population declines are driven by processes local to the northern Antarctic Peninsula. The loss of SSI AFS would substantially reduce the genetic diversity of the species, and decrease its resilience to climate change. There is an urgent need to reevaluate the conservation status of Antarctic fur seals, particularly for the rapidly declining SSI population.
Highlights
Rapid changes in the abundance of, or prey selection by, apex predators can fundamentally alter ecosystems through dynamic predator-prey interactions (Hairston et al, 1960; Paine, 1966; Dayton, 1971; Estes et al, 2011)
We emphasize that the loss of the South Shetland Islands (SSI) Antarctic fur seals (AFS) population would have a disproportionately large negative impact on the genetic diversity of the species, and reduce the species’ resilience to climate change
Drawn from a long-term data set of age-specific, and individually tracked behavioral and demographic metrics, multiple lines of evidence indicate both types of control are compounding to force a rapid population crash of the SSI AFS
Summary
Rapid changes in the abundance of, or prey selection by, apex predators can fundamentally alter ecosystems through dynamic predator-prey interactions (Hairston et al, 1960; Paine, 1966; Dayton, 1971; Estes et al, 2011). Antarctic Fur Seal Edge Population demands (Williams et al, 2004; Pagano et al, 2018). Despite this potential, regional-scale examples of such effects have been rare (Estes et al, 1998; Springer et al, 2003), and sometimes controversial (DeMaster et al, 2006; Wade et al, 2009); in part, because direct observations of predation are difficult to obtain in remote marine environments (Estes et al, 1998). The Antarctic fur seal (AFS, Arctocephalus gazella) is a key indicator species for the ecosystem-based management of the Antarctic krill (Euphausia superba) fishery (Boyd and Murray, 2001)
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