In the Southern Ocean, Antarctic blue whales have risen from an estimated 418 animals after the last reported catch in 1973 to about 4,018 today. The increase marks real progress after decades of protection, but the giants remain a tiny fraction of their former numbers.
Blue whales were hunted on a vast scale during the 20th century. Each can weigh more than 400,000 pounds, or 180,000 kilograms, and whalers sought them for their oil. The International Whaling Commission banned hunting in 1964, yet illegal Soviet whaling continued for another 10 years. By the time it ended, whaling had cut the Antarctic blue whale population by an estimated 99.8 percent.
A study published Nov. 5 in Endangered Species Research brings together the old catch records and newer sightings to estimate how the population has changed. Lead author Zoe Rand, a postdoctoral scholar at the University of Washington School of Marine and Environmental Affairs, and her colleagues combined historical whaling data with ship surveys and photo identifications. Their model estimates that about 1.9 percent of the pre-whaling population remains, and that numbers are now rising by 4.5 percent a year.
Counting the whales is difficult. They are large enough to be spotted from space, but spend little time at the surface. Researchers use line transect surveys, in which ships travel along set routes and record the whales they see, as well as photographs that help identify individual animals. The International Whaling Commission surveyed the whole Southern Ocean in expeditions from 1978 to 1984, 1985 to 1991, and 1991 to 2004. Few such ship surveys have taken place since, leaving scientists with a costly and incomplete picture.
The recovery matters beyond the whales themselves. Rand describes them as “ecosystem engineers.” When a whale dies, its enormous body sinks to the ocean floor, where many forms of life feed on it. These “whalefalls” help move nutrients through the ocean and may also store carbon. Restoring the population could therefore support life in the deep sea as well as return a missing giant to Antarctic waters.
There is reason for cautious hope, but no guarantee that the whales will regain their old numbers. They live for a long time and give birth to one calf at a time, usually every two to three years, so rebuilding a population devastated by whaling will take many generations. The animals are still listed as critically endangered, and researchers do not yet know how they will fare as environmental conditions change.
Rand hopes new tools, including passive acoustic monitoring, will make it easier to track them. Scientists can use whale-song recordings to estimate how many animals are in an area, though they have not yet worked out how to turn those recordings into a total population count. As Rand said, Antarctica is “not just one country’s ocean.” Continued monitoring across the vast Southern Ocean will be essential to tell whether this recovery holds and what comes next.