Late Holocene records of Antarctic fur Seal (Arctocephalus gazella) population variation on South Georgia, sub Antarctic

Abstract

The Antarctic fur seal (Arctocephalus gazella) population at South Georgia has increased dramatically through the 20th and 21st centuries following near extinction at the beginning of the 20th century. This rapid increase is now causing concern as the seals are damaging the coastal habitats of South Georgia including specially protected areas. To assess whether this population increase is part of a natural fluctuation or due to human induced changes in the marine ecosystem, the fur seal population has been reconstructed through the Holocene from seal hair abundance and geochemistry. Results from the fur seal hair abundance record show fur seals have been present at South Georgia for at least the past 3439 14C yrs BP and the population today is not unprecedented during the late Holocene. Although previous studies have found a correlation between fur seal populations and geochemistry, this study highlights that this is not effective at all study sites due to the complex relationship between climate change, catchment sediment delivery processes and seal population dynamics. At South Georgia, Cu and Zn are found to be indicators of fur seal activity once a threshold of 1500 hairs per 1 g of dry weight is reached. The fur seal hair abundance results suggest there is a link between fur seal populations and climate change. Although the largest increases in for seal population occur during cooler periods, the fur seal population is primarily controlled by prey availability (Euphausia superba), which is in turn influenced by climate change. Pre 200 yrs BP, an increase in prey availability is associated with colder periods, which are linked to changes in oceanography and led to a consequent increase in sea-ice extent. Post 200 yrs BP, the whaling industry has resulted in a krill surplus in the South Georgia region elevating krill availability, causing an increase in the fur seal population (that has been coincident with warming). Although the population has increased during the 20th and 21st century as a result of human induced causes, this increase cannot be sustained once the krill sumlus ceases, As the population has been at similar levels previously and the krill surplus is thought to be ending, it is concluded that the fur seal population increase during the 20th century is not abnormal and management of the fur seal population at South Georgia may not be necessary.