Hundreds Of Humpback Whales Are Massing In A Tiny Spot Of Ocean. Here’s Why.

2017-10-27T17:34:27+00:00 October 27, 2017|
Tagged humpback whales travel much further in the southwest Indian Ocean than previously thought. (Credit: Doug Perrine, NOAA Permit # 88)

(Click to enlarge) Nearly 200 humpback whales mill around a piece of ocean smaller than a U.S. football field for several months out of the year (Credit: Doug Perrine, NOAA Permit # 88)

HALIFAX, CANADA—In the fall of 1990, a few humpback whales showed up off the coast of western South Africa where they had rarely been seen before. Over the next couple years, a few more showed up, then a few more. Today, nearly 200 of the giant ocean mammals mill around a piece of ocean smaller than a U.S. football field for several months out of the year.

(From Science Mag / by Elizabeth Pennisi) —  Now, scientists think they know what’s luring what may be the largest global gathering of these cetaceans: masses of free food. Hungry humpbacks travel thousands of kilometers to feast on a rich buffet of tiny crustaceans called krill, researchers reported here this week at the biennial meeting of the Society for Marine Mammalogy.

Many animals are loath to change their behavior, particularly when it comes to food. But this—and several other studies reported here—reveals how readily humpbacks around the world come up with new hunting strategies, says Alexander Werth, a marine biologist at Hampden-Sydney College in Virginia who was not involved with the work. It also speaks to the ability of these animals to learn from each other and to develop efficient ways to eat.

Marine biologists Mduduzi Seakamela of the National Department of Environmental Affairs in Cape Town, South Africa, and Kenneth Findlay at the Cape Peninsula University of Technology, also in Cape Town, didn’t know all this for sure when they recruited graduate student David Cade to help them pin down what the whales were doing off their coastline. With the proper permits in hand, Cade—a Stanford University student who works at the Hopkins Marine Station in Pacific Grove, California—helped them outfit a dozen whales in the area with the research equivalent of a Go-Pro, a video camera that came with a motion detector and a depth finder. Together, these instruments revealed what the whales were doing underwater. What’s more, the ship where the researchers were working could monitor the density of prey in the water underneath it, so Cade could figure out what the whales were eating. 

Most of the time, the density of krill was random, and the whales’ feeding activity was slow and steady. But one afternoon, the whales all converged on one place where there was a really high density of prey—a 40-meter-thick swath of water with 107 grams of krill per cubic meter, as opposed to the average density of 66 grams per cubic meter, Cade reported at the meeting.

Once the whales had homed in on this smorgasbord, they did something no one had witnessed before. Under normal circumstances, groups of two or three whales tend to dive in synchrony across tens of square kilometers to hunt for food. During such dives, they lunge about 32 times per hour, accelerating quickly to suck in all the food and then spending about a minute between each lunge underwater. But in this dense patch of food, a free-for-all ensued. The whales were practically on top of each other, lunging about 53 times an hour and with barely half a minute’s rest.

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