Humpbacks are not the largest whale species—that distinction goes to blue whales—but they do boast the longest pectoral fins of any cetacean. While most cetaceans' pectoral fins are only one-seventh of their body length, a humpback's flippers can reach up to one-third of its body length. These massive fins help the whales navigate shallow waters, accelerate rapidly and increase their maneuverability. Now, a new study published in Royal Society Open Science has offered the first concrete evidence of humpbacks using their pectorals for another purpose: herding fish into their mouths.
Since as far back as the 1930s, researchers have theorized that humpbacks deployed their fins to corral prey, but it was a difficult hypothesis to prove; from the wrong vantage point, it can be hard to tell what the whales are doing as they thrash about in the water. Madison Kosma, a graduate student at the University of Alaska Fairbanks and lead author of the study, realized as much when she was riding in a boat and observed a whale hunting salmon off the coast of Alaska. The great mammal’s movements just seemed chaotic—but when she was later able to study humpbacks from a bird’s-eye view, with the help of a drone, Kosma realized that they were in fact deliberately using their fins during the hunt.
“It wasn’t chaotic,” she tells Ian Sample of the Guardian. “[I]t was actually graceful, intentional and calculated.”
With the help of new technologies, Kosma and her colleagues sought to document a unique role of humpback pectorals from a perspective that was not available to earlier researchers. They carried out their study in in Chatham Strait, along the shore of Baranof Island in Southeast Alaska, at times when young salmon are released from a hatchery there. Each April, according to National Geographic’s Tim Vernimmen, the Hidden Falls Hatchery releases the salmon into the ocean as part of an effort to replenish overfished populations, and several humpbacks have learned to show up to take advantage of the smorgasbord. The researchers took identification photographs of the whales, then documented them with the help of a camera, a GoPro affixed to a long pole—so they could view the animals from above while standing on a walkway near the hatchery pens—and finally with a drone.
The new report focuses on the behavior of two whales (dubbed “Whale A” and “Whale B”) that both displayed what the researchers call “pectoral herding” behavior. First, the whales would create a ring of bubbles that trapped their prey. Then, they seemed to use their pectorals in three ways: to create an additional physical barrier that stopped the fish from escaping, to swish the water about and usher the fish into their mouths, and to confuse the fish by flashing the white undersides of their fins. The confusion tactic was exhibited by Whale B, and only in sunlit conditions; the humpback would position its fins in a “V” shape and lunge vertically from beneath. The researchers suspect the light reflecting from the white fins disorients the fish, driving them into the whales’ mouths.
The study authors acknowledge that their sample size was small, and that more research is needed before conclusions can be drawn about whether pectoral herding is broadly used as a “principal foraging technique.” Yet the new report shows how modern technologies, like drones, can help scientists glean new insights into whale behavior—and also highlights humpbacks’ innovative nature. The animals have long been known to use bubble “nets” to trap prey, which seems to work well when hunting schooling fish that aggregate in one area of the net. But the researchers found that juvenile salmon do not cluster in this way, leading them to theorize that the humpbacks “independently altered their foraging strategies to accommodate non-schooling fish and more effectively incorporate hatchery-released juvenile salmon into their diets.”
“These animals are highly innovative,” the study authors add. “Maintaining a suite of foraging strategies probably aids humpback whales in a changing environment, where food availability fluctuates and competition may impact population dynamics.”