The Rapid Population Collapse of a Key Marine Predator in the Northern Antarctic Peninsula Endangers Genetic Diversity and Resilience to Climate Change

Summary

Antarctic fur seal populations at Cape Shirreff in the South Shetland Islands have collapsed by 86% since 2007, according to this study. The dramatic decline stems from two main causes: heavy predation by leopard seals, which kill an average of 69.3% of seal pups each year since 2010, and reduced food sources in the area.This population crash poses serious conservation concerns because the South Shetland Islands represent one of only four genetically distinct breeding groups of Antarctic fur seals. The loss of this breeding stock would reduce the species' overall genetic diversity. Interestingly, adult seals show good body condition during winter months, suggesting they can find adequate food in other locations. This indicates that local environmental changes around the Antarctic Peninsula, rather than ocean-wide food shortages, are driving the population decline.

This graph shows Antarctic fur seal pup counts (living and dead) from 1959 to 2020 across South Shetland Islands breeding sites. Gold triangles represent the entire archipelago, blue circles show Cape Shirreff data, and green squares indicate San Telmo Islets counts. This six-decade dataset reveals dramatic population changes and highlights the South Shetland Islands' role as critical breeding habitat. The comprehensive survey data provides essential baseline information for understanding population dynamics and the current conservation crisis facing this genetically distinct breeding stock.

Key Findings

Antarctic fur seal numbers at Cape Shirreff have plummeted by 86% since 2007, representing a severe local population crash.

Leopard seals kill an average of 69.3% of fur seal pups each year since 2010, with rates ranging from 50.3% to 80.9% annually.

Antarctic fur seals are not one uniform global population but rather four genetically distinct breeding stocks, making each group's survival crucial.

Female seals are spending longer periods away from their pups during foraging trips, indicating that prey has become scarcer in nearby waters.

Adult seals maintain good body condition through winter, suggesting the decline results from regional issues around the Antarctic Peninsula rather than ocean-wide food shortages.

The South Shetland Islands population represents a genetically distinct group that cannot be replaced by other fur seal populations, making its preservation essential for the species' long-term resilience.

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.

Published in

Frontiers in Marine Science

2022

Authors

Krause, D.J., Bonin, C.A., Goebel, M.E., Reiss, C.S., Watters, G.M.

Institutions

Antarctic Ecosystem Research Division, Southwest Fisheries Science CenterMarine and Environmental Science Department, Hampton University

Methods

FieldDataCaseBiological sampling

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