Study tracks cetacean circumpolar navigation
By Summit Voice
SUMMIT COUNTY — Antarctic blue whales are recovering slowly from the brink of extinction, and a new study showing high genetic diversity among the cetaceans that survived the slaughter is a hopeful sign for the future.
Blue whales are the largest living animals. They were though to number about 250,000 before intensive whaling in the 20th century reduced their numbers to just a few hundred. Blue whales are still listed as endangered on the IUCN Red List.
“Fewer than 400 Antarctic blue whales were thought to have survived when this population was protected from commercial hunting in 1966,” said Angela Sremba, who conducted the circumpolar study as part of her master’s degree with the Marine Mammal Institute at Oregon State University’s Hatfield Marine Science Center.
“But the exploitation period, though intense, was brief in terms of years, so the whales’ long lifespans and overlapping generations may have helped retain the diversity. In fact,” she added, “some of the Antarctic blue whales that survived the genetic bottleneck may still be alive today.”
As part of the study, the researchers examined 218 biopsy samples collected from living Antarctic blue whales throughout the Southern Ocean from 1990 to 2009, through a project coordinated by the International Whaling Commission.
The biopsy samples were collected during more than two decades of research cruises supervised by the International Whaling Commission, and with international scientists joining research vessels from the Japanese Ministry of Fisheries.
“These animals are very long-lived – maybe 70 to 100 years – and they can grow to a length of more than 100 feet and weigh more than 330,000 pounds,” he said. “There is a jawbone in a museum in South Africa that takes up most of the lobby. This is one reason they were so intensively exploited; they were the most valuable whales to hunt.”
Despite their history of exploitation, little is known about modern-day movements of Antarctic blue whales, which are considered a separate subspecies – differing in size and habitat use – from the smaller “pygmy” blue whales, which live in more temperate regions of the Southern Hemisphere.
Through “microsatellite genotyping,” or DNA fingerprinting, the PLoS ONE study was able to track some of the movements of individual Antarctic blue whales.
“We documented one female that traveled from one side of Antarctica to the other – a minimum distance of more than 6,650 kilometers over a period of four years,” said Sremba, who is now continuing her studies as a Ph.D. student in the Department of Fisheries and Wildlife at OSU. “It is the first documentation of individual movements by Antarctic blue whales since the end of the commercial whaling era.”
Baker said the long distance movement of a few individuals was “somewhat surprising” in comparison to the evidence for genetic differences between areas of the Southern Ocean. On one hand, it is apparent that individual Antarctic blue whales are capable of traveling enormous distances in search of food.
“On the other hand,” Baker said, “there seems to be some fidelity to the same feeding grounds as a result of a calf’s early experience with its mother. This ‘maternally directed’ fidelity to migratory destinations seems to be widespread among great whales.”
There is much, however, which scientists still don’t know about Antarctic blue whales, Baker explained. “Only now are we developing the technology to study such a small number of whales spread across such a vast habitat,” he said.
Now that their population is slowly recovering, future studies may focus on Antarctic blue whales’ migration patterns, and the locations of their breeding and calving grounds.
Results of the study have just been published in the open-access journal, PLoS ONE.