Research - English version

The porpoise is the only toothed whale that breeds in Danish waters. It is a cousin of the dolphin but has a different set of behaviours (for example, it is shyer).

Whales, like human beings, are mammals that breathe with lungs. They give birth to live calves, and although the porpoise both gives birth to its calves and lives its whole life underwater, it must periodically rise to the surface and draw air. Its breathing hole, which is similar to our nose, sits on top of its head, so it does not have to stick its whole head out of the water to take in air.

Although porpoises are very common in Danish waters, not much is actually known about these small whales. Therefore, Fjord&Bælt has received permission from the Danish Environmental Protection Agency to keep up to four porpoises and train them so that they can actively participate in the research work.

The porpoise is sent back and forth in Fjord&Bælt's sea pen, depending on where a fish is thrown into the water. The experiments are performed both with and without special soft cup blinders attached around their eyes to study the significance of vision and echolocation in catching their prey.

Through these studies, a detailed understanding of how porpoises use and regulate sounds during the prey capture sequences has been obtained. It is the first time details of this kind have been documented concerning the whales' hunting behaviours. The results can be used to better understand how porpoises catch prey and, hopefully, how to avoid getting them caught in fishing nets while they hunt.

In recent years, improved acoustic measurements have totally changed the possibilities of studying marine mammals in the wild. Equipment is attached with suction cups to porpoises and other whales, and records the sounds the animal produces and the sound universe found in the animal's surroundings. In addition, the equipment registers diving depth and the animal's movement and orientation in the water. Today, the animal's heart rate can also be recorded. Overall, we get an almost complete picture of how the animal is affected when, for example, a boat passes them or when they approach a windmill out at sea. Aarhus University, as well as the Woods Hole Oceanographic Institution in the USA and the University of St Andrews in Scotland, is a world leader in the development of measuring instruments, and the porpoises at Fjord&Bælt contribute knowledge so that data collection and analysis have become very accurate. The University of Southern Denmark uses the same measuring equipment to register the porpoises' hearing while they swim around freely. The picture shows suction cups with electrodes, which are attached to the animal's back and collect data on the porpoise's brain activity, which can then be used to learn about the animal's hearing. The first tests on the porpoise Freja have exceeded all expectations, and in the next phase, wild porpoises and other toothed whales will be examined using this technique. In the long term, these methods can be used to measure hearing on whale species, for which we do not currently have data. How, for example, does a blue whale hear? The new methods will hopefully help us gain more knowledge about this and many other questions about marine mammal hearing.

To better understand how porpoises use sounds to find prey and orient themselves underwater, two studies have been conducted. It has been investigated how the porpoise's hearing works during echolocation and how porpoises use their sonar during active echolocation.

With its sonar, the porpoise can, for example, point out which of two spheres is made of aluminum (the other is made of plastic). And what is most remarkable is that it has special soft cup blinders attached around its eyes so it cannot use its sight in this test.

The use of DNA analysis in science is advancing very rapidly. Tiny DNA fragments in bones helped to completely change our understanding of human origin. Now, eDNA (environmental DNA) can be used to find rare and endangered species of fish and other animals in a lake. But can one also use eDNA to find out if there are porpoises in an ocean area? And can one even count the animals using eDNA?

Andrew Foote from the University of Copenhagen's Center for Geogenetics analysed water samples at different distances from the porpoise fence at Fjord&Bælt and inspected the water for porpoise DNA. It turned out that in a small shot glass with seawater, he could identify DNA from porpoises in every third water sample within 10 metres of the fence. Since Foote's article came out in 2012, this technique has been refined so that researchers can now conduct extended field studies to investigate whether eDNA can help us in the management of marine mammals. Read the article here.

Studies have been done on the song of the harbor seals across most of their distribution area, but they have never actually been researched in Denmark. From studying other areas, we know that the seal song sounds different in diverse geographical areas.

It is said that the seals have different dialects. Exactly what dialect the Danish seals have is part of  Puk Sabinsky's special project at Fjord&Bælt and the University of Southern Denmark. She travels around the Danish waters and makes sound recordings which she will later compare with those we know from, for example, Sweden, Norway and Scotland.