FREEZE & FLIGHT RESPONSE
When animals are exposed to threatening stimuli, they display avoidance behaviors. These behaviors are categorized as flight or fight reactions and freeze reactions. According to "Escaping narwhals can freeze and flee at the same time," when an animal senses danger, it might freeze to try to avoid being seen. Or it might flee, to try to get away. However, when narwhals encounter people, they do a bit of both, a new study finds. After escaping from a net, these whales dove deep underwater. This reaction appears to be a fleeing or a flight response. Yet at the same time, their heart rates and breathing slowed, as if they were trying to hide. Normally during intense physical activity, the heart races. This helps pump more blood, oxygen, and nutrients to working muscles. A narwhals' escape dives definitely qualifies as intense activity. During those dives, they pump their tails at rates up to 25 strokes per minute.
An ecophysiologist at UC Santa Cruz, Terrie Williams, studies how animals' body functions affect how they interact with their environment. She commented on the narwhals' paradoxical escape response: "There are other marine mammals that can have heart rates that low, but not typically for that long a period of time. And especially not while they're swimming as hard as they can." To evade natural predators such as killer whales, narwhals do not usually dive away. Instead, they tend to hide. They may sneak under ice sheets or huddle in spots too shallow for their pursuers, Williams notes (Williams et al., 2017).
But in response to people, they often dive quickly and disappear from sight. During escape dives, their heart rates went down to levels of three and four beats per minute. And they stayed at that level for ten minutes at a time. Observations made by Williams' team noted they dove deeply--45 to 473 meters down. Such dives burned about twice as much energy as normal feeding dives. These post-escape dives burn up to three to six times more energy than when the animals were at rest. Frantic getaways, combined with super-low heart rates, take a steep toll. Escape dives gobbled up 97% of the available oxygen in the narwhal's lungs, blood, and muscles. That is almost 52% used up during normal dives of similar depth and duration (Quintanilla, 2018).
Narwhals have a resting heart rate of about 60 beats per minute. That’s similar to people. They can lower their heart rates when diving, however. This conserves energy during long stretches underwater.​ Now researchers have observed narwhals’ heart rate dropping precipitously low when diving to escape from humans. As melting sea ice opens up the Arctic to more human activity, the mammals, known as “unicorns of the sea” for their single tusk, may be more exposed to the potentially harmful escape response, scientists say.
Fig. 4. Empirical probability density functions (epdfs) of habitat use by narwhal as a function of distance from shore during the exposure and postexposure periods mapped onto Admiralty Inlet visualizing large change in apparent habitat preference of narwhal when exposed to killer whales. https://www.pnas.org/content/114/10/2628/tab-figures-data
According to "Sustained disruption of narwhal habitat use and behavior in the presence of Arctic killer whales," using data from concurrently tracked predators (killer whales) and prey (narwhal), shows that the presence of killer whales significantly changes the behavior and distribution of narwhal. When killer whales were present (within about 100 km), narwhal moved closer to shore, where they were presumably less vulnerable. Under predation threat, narwhal movement patterns were more likely to be transiting, whereas in the absence of threat, more likely resident (Breed, et al., 2017).
Killer whale call playback experiments and direct observations of attacks show immediate strong evasive responses to killer whales in a variety of marine mammal prey. Field notes, Inuit observations, and more recent scientific work describing killer whale attacks on narwhal indicate that narwhal similarly initiates evasive behaviors during or immediately after killer whale attacks. These findings indicate that behavioral changes can extend beyond discrete predation or attack events. The mere presence of killer whales in a system can cause relatively large and persistent changes in behavior and space use in prey species.
As noted by "Narwhals and seismic exploration: Is seismic noise increasing the risk of ice entrapments?," the usual escape response of narwhals exposed to killer whales (Orcinus orca) or Inuit hunters involves prolonged submergence and entry into dense pack ice if this is available (Williams et al., 2010, Laidre et al., 2006). In other words, they tend to hide or flee slowly and cryptically to avoid predators. Their observed response to an icebreaker was similar (Finley et al., 1990) and this is in contrast to the responses of other cetaceans with locomotor muscles divided equally into slow-twitch and fast-twitch fiber types, allowing for high-speed movement away from a disturbance (Ponganis and Pierce, 1978).
Persistent disturbance of narwhals (and other acoustically sensitive Arctic species) could disrupt important behavior, cause the animals to abandon important summering areas, and change their migration patterns. As they leave the summering grounds, narwhals are generally heading towards winter feeding grounds, and disturbance could cause them either to return and risk ice entrapment or to move to wintering areas that are sub-optimal for feeding. Considering that narwhals already appear to be approaching their physiological capacity and may have little flexibility to adjust their swimming and diving behavior (Williams et al., 2010), it seems critical that the whales are not disturbed to such an extent that their basic annual cycle is disrupted.