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Narwhals – the unicorns of the sea – show a strange response of fear after becoming entangled in nets. Scientists say that this unusual reaction to human-induced stress could restrict blood flow to the brain and leave the whales confused.
Narwhals swim hard and dive to escape after being released from a network, but at the same time their heart rates dramatically plummet, according to a report recently published in Science . It is almost as if they were trying simultaneously to freeze and flee.
"This is an unusual reaction to an unusual type of threat," says Terrie Williams, a researcher at the University of California at Santa Cruz. "I do not think this is the normal response when animals are being chased by a killer whale."
Male narwhals have a distinctive long spiral tusk, and these elusive creatures live in the north in the Arctic. They are not easy to study, since they live a large part of their lives surrounded by darkness and ice. But scientists sometimes control their movements by trapping them with nets and tagging them in the summer, when whales are more accessible.
Williams and his colleagues recently traveled to the waters off Greenland's east coast to equip narwhals with technology that allows researchers to monitor marine mammalian heart rhythms, swimming movements and other data.
"This is the first time there has been a long-term record of an ECG for a wild cetacean," says Williams, who has used similar monitors on dolphins. and stamps "I do not know if there is something like that".
In the first dives after the narwhals were released from the nets, he says, his heart rate dropped from 60 beats per minute to three or four beats per minute. This lasted approximately 10 minutes.
"And I've never seen that in any animal for which I have registered a heart rate," he says. "So that was the first clue that we were seeing something very different here."
In addition, the whales swam rapidly during this time. "They exercised as fast as the narwhal exercises," says Williams. "They swam constantly, they try to make a flight response superimposed on a freezing response like down-regulation, and I have not seen that before."
Makes you wonder how whales can get enough oxygen to their brains. And he also wonders if this could have any relevance to the mysterious strandings of other whales that dive deep.
Kristin Laidre, a research scientist at the Polar Science Center at the University of Washington who has studied narwhals, says that this is "really interesting document that provides a new physiological angle on the vulnerability of narwhals to anthropogenic disturbance in the Arctic. "
The loss of sea ice in the Arctic, says Laidre, means great changes in the ecosystem, plus a sudden interest in more industrial development, resource extraction and new shipping routes. "All those things mean discomfort for the narwhals," she says. "As far as I know, this is really the first time we quantified the effects of physiological disturbances in the narwheels, so they are really important data."
Because the narwhals have lived a life far to the north, surrounded by dense sea ice, they have been relatively isolated from human activity. "Any kind of disturbance," says Laidre, "is going to be a fairly new thing, potentially very disturbing for a species that has existed in an environment like that for so long."