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Humpback Whales Herd Salmon With Their Fins, New Photos Reveal

2019-10-25 21:38| 发布者: hujian| 查看: 27| 评论: 0

摘要:   Humpback whales are well known for their sophisticated hunting strategies, such as blowing bubbles to form wide nets, then swimming in a clockwise motion to swiftly encircle their prey.  This in ...

 


 Humpback whales are well known for their sophisticated hunting strategies, such as blowing bubbles to form wide nets, then swimming in a clockwise motion to swiftly encircle their prey.

  This ingenuity, coupled with the marine mammals’ advanced social behaviour and communication, led scientists to suspect they were missing something.

  It turns out they were right.

  Each April, a salmon hatchery in southeastern Alaska>

  Watch humpback whales corral juvenile salmon with their flippers.

  In doing so, they recorded a behaviour never before confirmed by scientists.

  After blowing a bubble net, two whales used their flippers to create a second barrier inside the bubbles, moving the appendages up and down to direct the fish toward their gaping mouths, according to a new study, published today in the journal Royal Society Open Science.

  Anecdotal evidence of this so-called "pectoral herding" exists, but in those cases, it was too hard to tell what was really going on, says study leader Madison Kosma, a master’s student in fisheries at the University of Alaska Fairbanks.

  “Now, thanks to the unique situation at the hatchery, and thanks to new technologies such as drones, we were actually able to document it,” says Kosma, whose team witnessed pectoral herding dozens of times over the three-year study.

  “The only way you could get closer is if you’re a fish in their mouth,” she adds.

  A humpback whale collects young salmon with its fins in southeastern Alaska.

  PHOTOGRAPH BY MADISON KOSMA

  It’s unknown whether humpbacks elsewhere use this technique, or what prompts the animals to use it. But what’s clear is humpback whales are even more adaptable than thought, and could>

Working for their dinner

  For the study, Kosma and colleagues set up experiments in various bays along the eastern shore of Baranof Island, timed to coincide with the>

  The team>

  In some cases, the scientists stood on walkways attached to hatchery pens and extended an 11-foot pole with a camera attached over the water to record the action. Back at the lab, the team analysed the footage and assembled frame-by-frame feeding sequences, as well as 3-D modelled the foraging.

  The results showed that the whales herded salmon with their flippers for three reasons: To trap the fish; to move water, which then directs the fish; and to scare the fish to the surface by flashing their fins' light-coloured underside, a behavior only observed in sunny weather.

  Kosma jokingly refers to the last strategy as a referee field goal position, because one video shows a whale swimming up toward the salmon with its fins stretched out in a V above its head.

  “From a hydrodynamical perspective, holding your fins like that would be a waste of energy,” she says, “so they must have a good reason for doing this, like catching more fish.”

FollowVideoWhales Team Up in Amazing Bubble-Net HuntIn the summer, southeastern Alaska's waters teem with humpback whales that have migrated north to feed on herring and other fish. One of their most fascinating behaviours is bubble-net feeding, a complex and coordinated tactic for capturing many fish at once. Andy Szabo, director of the Alaska Whale Foundation, and naturalist Steve Maclean explain the phenomenon while aboard the National Geographic fleet on a recent voyage to Alaska's Inside Passage.loading...

  As for why the whales use pectoral herding, Kosma suspects it’s because the inexperienced fish require more work to catch.

  Since lunging at prey with their mouths wide open is quite tiring for the whales, they need to make sure their prey are dense enough to make it worthwhile. However, when threatened, juvenile salmon don’t school together the way other prey species like herring do—so corralling the salmon with their flippers may be needed to move them closer together.

  An aerial image shows a humpback gathering fish with its flippers. The behaviour was observed dozens of times during the three-year study.

  PHOTOGRAPH BY MADISON KOSMA

Trapped

  Frank Fish, a biologist at West Chester University in Pennsylvania who has studied the biomechanics of whale fins, agrees “this research definitely shows that the flippers can concentrate prey.”

  Humpback whales have very long flippers>

  “The main lesson I take away from this study is that humpbacks are capable of innovation and learning new foraging strategies that may help them to feed more effectively on specific prey species,” says Christie McMillan, a whale expert at the Marine Education & Research Society in British Columbia, Canada.

FollowPhotosAMAZING PICTURES OF WHALESloading...
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  Grey whales like this one migrate up to 16,093 kilometres a year, from the warm waters of Baja California to their feeding grounds in the Bering Sea.

  PHOTOGRAPH BY THOMAS P. PESCHAK, NAT GEO IMAGE COLLECTION

  She knows this firsthand: McMillan recently described a newly observed behavior she calls trap feeding, in which some humpback whales near Vancouver Island hold their mouths open at the surface where birds are feeding—an apparent attempt to fool fish into seeking refuge in their mouth.

  “But it is unclear how long it takes whales to learn these new strategies,” McMillan notes, “and therefore whether they will be sufficient to allow them to respond effectively to climate change and the depletion of their prey.”

Lead Image: A humpback whale surfaces while feeding on herring in Norway. A population of humpback whales in Alaska has been observed corraling fish with their flippers.

  PHOTOGRAPH BY PAUL NICKLEN, NAT GEO IMAGE COLLECTION



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