In 2014, nine blue whales died after becoming trapped by ice near Newfoundland, Canada. Two of their bodies washed ashore and began to inflate as they decomposed, prompting concerns of an imminent explosion and possibly inspiring a skit on “Saturday Night Live” that ended with Charlize Theron covered with whale guts. More recently, the colossal carcasses of these unfortunate mammals have made significant contributions to science.
Nearly a decade after their deaths, researchers analyzed the beached whales’ DNA – along with samples collected from 26 other blue whales – to establish the maximum accurate picture to date of the population structure of the North Atlantic. The results, published this month in the journal Conservation Genetics, reveal a ticking time bomb in blue whale demographics, strange migration patterns and even hidden matings between species.
The global population of blue whales was severely damaged by industrial whaling in the early 20th century. A declining population can increase inbreeding rates, which can reduce the diversity in a population’s gene pool and increase the risk of species extinction.
With fewer than 3,500 adult blue whales remaining in the North Atlantic, scientists expected to find such a genetic barrier. At first, they were surprised when their genomic analysis showed no signs of one. They say it may be because of the time it takes blue whales to reproduce – about 30 years to go from one generation to the next.
“It probably wasn’t enough time to really see a bottleneck effect,” said Mark Engstrom, a genomicist at the Royal Ontario Museum in Toronto who oversaw the research effort.
That North Atlantic blue whales have “preserved their genetic variation despite about a century of industrial whaling” is good news, said Axel Jahnke, a genomicist at Goethe University in Frankfurt in Germany who was not involved in the study.
But if the population doesn’t increase over the next century, Dr. Engstrom said, he would expect a bottleneck to appear — to the whales’ detriment.
Whalers historically believed that blues in the North Atlantic split into distinct eastern and western populations. But whale DNA tells a different story. Dr. Engstrom’s team found a lot of evidence for East-West mixing.
“There are differences,” he said, “but this is a fairly recent division.” Most of the time, genes flow from western blue whales to those in the east. The team speculates that this movement may reflect the North Atlantic Current, in which seawater flows from west to east. Right whales may follow their favorite food, krill, as waves wash the shrimp-like crustaceans eastward, where they encounter a different population of whales.
Even more amazing is that genes cross evolutionary lines as well as geographic ones.
Blue whales have long been known to mate and breed with fin whales, even though the two aren’t particularly close relatives—and blue whales can be up to 25 feet longer and up to 85 tons heavier. Many hybrid animals (such as mules, for example) are sterile. But armed with their new data set, Dr. Engstrom’s team found evidence of persistent mixing between species. In total, about 3.5 percent of the blue whale genome comes from fin whales.
“This is fantastic,” said Dr. Janke. He had previously looked for blue whale DNA in whale fin genomes and found none. The new data, combined with an analysis carried out by the team of Dr. Engstrom, suggest that although the hybrids are not sterile, they mate only with blue whales.
“What traits are transferred from the fin whale to the blue whale?” asked Dr. Janke. He wonders if these genes benefit blue whales in any way.
Dr. Engstrom plans to collect more blue whale genomes, which Dr. Jahnke hopes could help scientists understand populations in other parts of the world. It’s a big ocean, and with dwindling blue whale numbers, he said, knowledge is power.
“There’s kind of a motto that we have,” Dr. Janke said. “You can only protect what you know.”