South Georgia Blue Whale Aggregation Signals Potential Species Rebound
A gathering of blue whales near to the sub-Antarctic island of South Georgia may signal a rebound in the population of the world's largest living animal. The 'unprecedented' sighting follows a 30-year moratorium on whale hunting, which had previously forced blue whales to the brink of extinction.
During an expedition led by British Antarctic Survey (BAS), 55 blue whales (Balaenoptera musculus) were sighted around South Georgia, where seasonal blooms of krill attract a number of filter-feeding species of whale, including humpback, fin, minke and southern right whales. During the first half of the 20th century, the rich feeding grounds around the island drew hunters to the region, during which time an estimated 42,000 blue whales were slaughtered by the whaling stations around South Georgia. Globally, the population of Antarctic blue whales was decimated, reduced from an estimated 126,000 mature individuals in 1926 to less than 1,000 by the late 1960s, according to data from the IUCN. The total global kill over 60 years is thought to have been more than 350,000 individual animals.
According to a report on the BAS website, Antarctic blue whales were detected acoustically but sighted only once during a 2018 survey of South Georgia. Less than two years later, 36 sightings were recorded with 55 individual animals seen, suggesting that the Antarctic blue whale population is showing signs of recovery, and that South Georgia's waters remain an important feeding ground for the species.
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Thanks to the abundance of whales sighted during the survey, the team were able to take ID photographs and collect skin samples from the animals. Photographic ID is important for tracking the whales as they migrate around the globe, and the skin samples will help to determine their diet and assess the genetic diversity of blue whales following the massive reduction in their population.
The BAS survey team also reported that humpback whale populations are in excellent health, and are now a common sight around the South Georgia coastline, with 790 humpbacks sighted over 21 days of the survey. The number of humpbacks seen during the previous year indicates that more than 20,000 whales are seasonally migrating to the area, suggesting that the population is 'very close to full recovery.'
Whale project leader Dr Jennifer Jackson, a whale ecologist at BAS, said: 'After three years of surveys, we are thrilled to see so many whales visiting South Georgia to feed again. This is a place where both whaling and sealing were carried out extensively. It is clear that protection from whaling has worked, with humpback whales now seen at densities similar to those a century earlier, when whaling first began at South Georgia.'
The full report of the BAS team's recent survey of South Georgia can be found at: www.bas.ac.uk/media-post/return-of-the-whales-to-south-georgia, and for a more in-depth report on the blue whale study, read team leader Dr Jennifer Jackson's blog at: www.bas.ac.uk/blogpost/blue-whale-comeback-at-south-georgia .