Humpback whales have long been thought of as solitary creatures—they spend most of their time solo, sometimes moving in pods of two or three. But on rare occasions, the creatures meet in the polar regions to feed in what is known as a "supergroup," containing 10 to 15 animals. But new research is challenging the notion of the solitary humpback, detailing several sightings of supergroups with up to 200 animals, reports Mallory Locklear at New Scientist.
Scientists found these massive supergroups during research cruises in 2011, 2014 and 2015. The gatherings occurred in the Benguela Upwelling System, ocean currents off the southwestern tip of South Africa between St. Helena Bay and Cape Point. The groups were not only surprising for their size, which ranged from 20 to 200, but also the time of year in which they were spotted. Scientists recorded their presence off the African coast in October and November (late summer in South Africa) when they typically migrate to Antarctic waters to feed.
The whales were clearly feeding, according to the new study published in the journal PLOS One. The researchers observed the whales diving vertically, turning tightly and performing other maneuvers that indicated they were feeding. The color of their poop and a fishy odor while clearing their blowholes also suggested that they were mid hunt.
“I’ve never seen anything like this,” Ken Findlay lead author of the study from the Cape Peninsula University of Technology in South Africa tells Locklear.
So what’s behind this whale jamboree? The researchers lay out four possible scenarios. First, an increase in available prey may be drawing the whales to the Benguela System. According to the paper, predatory fish caught near the whales were stuffed with mantis shrimp, stomach contents that matched those of a humpback whale studied in 1990 that died after getting entangled in rock lobster fishing gear. A second possibility is that recent increases in humpback numbers are putting more pressure on food supplies, pushing the whales into new hunting territories. A third alternative is that whale numbers have increased, causing them to return to a hunting strategy used in the past.
A final option, according to the researchers, is that the whales have been summer hunting in Benguela all along. “It’s possible that the behavior was occurring but just not where it was visible. Because there were so few of them, we may not have seen it,” Findlay tells Locklear.
In the last two decades, however, humpback numbers have rapidly increased. Recent reports suggest they've reached 90 percent of pre-whaling numbers on the west coast of Australia and over 60 percent on the east coast. The whales are even re-colonizing urban areas like New York Harbor and globally have reached around 150,000 individuals. “For the last few decades, suddenly they seem to have overcome some threshold and have begun to increase very fast,” Gísli Vikingsson, head of whale research at the Marine and Freshwater Research Institute in Iceland tells Locklear.
It’s possible that as the numbers increase, researchers will begin to see other behaviors that were somehow hidden or interrupted by their previously low numbers. Chambers reports that the researchers hope to continue their study the whale parties and figure out what types and concentrations of prey are drawing the whales to Benguela.