During the late 19th to the early 20th centuries, the whaling industry reduced the population of humpback whales across the globe to near extinction. But now, the large mammals known for their haunting songs may be bouncing back in some places. Recently, more female humpbacks in the Southern Ocean are giving birth to more calves, reports Karen Weintraub for The New York Times.
From 2010 to 2016, researchers collected skin and blubber samples from 577 humpbacks using a crossbow with modified darts. By sequencing DNA, the team determined that that population included a total of 239 males and 268 females. Higher levels of the hormone progesterone in the blubber showed that an average of 63.5 percent of those females were pregnant when sampled. But the story is in how those numbers changed, not the average.
The proportion of females increased from 50 percent to 59 percent during the six years. And the percent of pregnant females surged from 59 to 72, the researchers report in Royal Society Open Science. Altogether, the findings suggest "a population that is growing rapidly," they write.
Most of the humpbacks were probably born after the International Whaling Commission (IWC) called for a moratorium on commercial whaling in 1982, Ari Friedlaender, a marine ecologist with Oregon State University and the University of California, Santa Cruz, and lead researcher in the new study, tells the Times. (Some regulations to prevent overhunting had been established when the the IWC formed in 1946, according to National Geographic.) The IWC, with 87 member countries, still manages whaling by setting catch limits for indigenous communities. The moratorium is still in place, though non-member countries such as Japan and Russia flaunt it.
The moratorium certainly helped the whale population rebound, but the humpbacks may also be benefiting from climate change, for the moment. Less winter sea ice in the Antarctic means more open ocean where the whales like to feed on krill.
The region around the Western Antarctic Peninsula has experienced some of the greatest effects from climate change, writes Yasemin Saplakoglu for Livescience.com. The trend has given the whales 80 more days of hunting in the year. But the researchers write that in the long term, warming ocean waters and less sea ice could lead to less krill and harder times ahead for the whales. When that may happen is difficult to predict, since data on how the rebounding whales affect the krill populations is scant. But already, research teams have noted a decline in krill populations, reports Andrea Thompson for Climate Central.
Not all the whales in the region are benefiting from sea ice changes. The Antarctic minke whale seems to prefer hunting near pack ice, according to a blog post by Robert C. Brears for The Maritime Executive. Like many whales, researchers still have a lot of quesions about minke's habits but one thing is clear: declining sea ice isn't good news for them. “There are way fewer minke whales in this area than you would expect, and enormous numbers of humpback whales," Friedlaender told Douglas Fox in a 2016 story for National Geographic. "It’s almost staggering.”
Keeping whales in the worlds oceans has importance beyond simply assuring the future of a charismatic animal. Whales are critical parts of healthy ocean ecosystems. Some of that is due to their sheer size: Large whales that feed deep and return to the surface to breathe mix nutrients and in doing so support life throughout the water column, writes Brian Clark Howard for National Geographic. Migrating whales likewise move nutrients from different latitudes.
The declines in whale populations after commercial whaling were so profound that researchers are only now beginning to understand the importance of having whales in the ocean.