Humpback Whales Are Starving, and Climate Change Is to Blame
Two months ago, a dead humpback whale washed up onto the beaches of Washington state.
Although the cause of its death remains a mystery, initial observations found that the whale was overly thin, with little blubber and little of its associated oil, which humpbacks use for fuel and warmth.
It was not an isolated occurrence. In Western Australia, the number of humpback whale stranding events has been on the rise for the past several years. The region used to see just two or three dead whales a year; that has now increased to dozens per season. As with the humpback in Washington, tests down under have revealed that most of the dead whales in Australia also had low blubber levels. Experts described the animals as “extremely malnourished.”
The exact cause may never be known, but new research has emerged that suggests that the deaths will continue.
The humpback whales that migrate to Australia rely on Antarctic krill for most of their food. They gorge themselves for three months while in the Southern Ocean and then fast during their months-long journey to their breeding grounds off the coast of Western Australia, 6,000 to 11,000 miles away. That requires packing away an awful lot of calories before they hit the road.
So, Why Should You Care? Krill, however, is in short supply these days. The tiny oceanic crustaceans depend on sea ice for their habitat because they eat algae that grow underneath the ice. Sea ice, meanwhile, is in decline in many areas of Antarctica owing to the effects of climate change. Previous research has indicated that krill populations have dropped by as much as 80 percent since the mid-1970s. Species such as whales and penguins depend on krill for survival.
This means humpback whales have a lot less to eat, and they may not be able to build up enough fat reserves for their 10,000-mile migration. That could leave them exhausted and less able to survive, according to research published in two new papers led by Janelle Braithwaite, a marine biologist and Ph.D. student at the University of Western Australia.
The first paper, published in the journal Polar Biology, looked at historical records to understand how krill abundance affects the health of humpback whales. Records for krill levels in decades past do not exist, but we do know how much oil used to be extracted from whales caught off the coast of Western Australia between 1947 and 1963. Scientific samples taken more recently indicate that the whales today have much lower oil content in their blubber, a sign that the whales are not as healthy as they were 50 years ago.
The second paper, published in the journal Conservation Physiology, looked at how much energy humpback whales need to complete that long migration. Braithwaite and her fellow researchers calculated exactly how much energy whales expend as they swim and how much more they need to use if their migration patterns are disturbed by shipping vessels, mining activities, fishing, and other things that get in their way.
The conclusion: Many whales, especially mothers who recently calved and need to feed their young, could start running out of energy during their long migration and die from exhaustion.
“Our research shows that the body condition of whales can be affected by changes in sea ice,” Braithwaite said.
The next step is to figure out what sea-ice levels would pose the most risk for humpbacks. “At the moment it is difficult to say whether conditions at the moment are risky, or how this will change in the future,” she said. “From our research, all we can say is that if sea ice declines in the future, then this will have consequences on the food source and migration condition of humpback whales.”
Until we know more, Braithwaite suggested that it might be time to take proactive steps to protect humpbacks at the tail end of their long migration, when they might be the most depleted and any disturbances could push them over the edge.
For example, she pointed to Western Australia’s Exmouth Gulf, which she said “is an important resting area for southbound migrating humpback whales. This area is also a hubbub of human activities, such as those associated with offshore mining. Adjusting shipping movements and speeds around the Exmouth Gulf area during these resting times would minimize disturbance and reduce whales spending any unnecessary energy.”
This new research comes less than two months after the U.S. Fish and Wildlife Service proposed removing most humpback whale populations, including those off the coasts of Australia, from the endangered species list.
“It is great news that many of the humpback whale populations have been reclassified as no longer being on the endangered list,” Braithwaite said, “but yes, our research indicates that there are other threats to migrating humpback whales that are much more subtle than directly killing whales.”