August 22 – We have been lucky, extremely lucky, to deploy 4 Acousonde acoustic tags on narwhals and find them in good shape out on the open sea between waves and blocks of ice! We are one step closer to understand the natural behaviour of narwhals and also how does changes in their surroundings affect their behaviour.
Acousonde (www.acousonde.com) is a behavioural tag that records both sound and movement. From these data we are able to reconstruct the exact path of the whale: at what depth it is diving, how it is orientated in the water column – swimming upside down or doing somersaults – and what it is saying and hearing.
Narwhals make many different types of sounds that they use for communication, for foraging and for finding way. Like all toothed whales, narwhals use echolocation to find their way and find their prey. While echolocating, the whale emits high frequency and short duration clicks that bounce off objects in the water. By listening to the echoes of these clicks, the whale can determine what it is facing – an iceberg, another narwhal or maybe a juicy Greenland halibut – and how far ahead this object is. If the narwhal has found a fish that it wants to catch, it will start to click more and more frequently while it approaches the nothing-expecting fish. The closer the whale is to the prey, the shorter is the time between the subsequent clicks – until the clicks in our ears melt together in time and create a buzzing tone. This sound, which is called a buzz, is considered to be a sign of a foraging event or at least an attempt to catch something.
Combining acoustic data with depth data gives us an idea at which depths and how often do narwhals forage. Finding prey is an important part of the life of any animal and we look forward seeing if the sound experiment we have conducted has affected their foraging behaviour.