Satellite tracking harbour porpoises

After seven days waiting for good weather, on 25 July 2012 researchers finally succeeded in driving two porpoises into the hunters' salmon nets. The animal is held without getting wound up in the top part of the net and without receiving any appreciable cuts. It struggles and slaps its tail fin, but soon calms down. Photo: Mads Peter Heide-Jørgensen.
Wildlife Computers, a company that specialises in tagging technology for marine animal applications, custom designed the transmitter for the porpoise's dorsal fin. Photo: Mads Peter Heide-Jørgensen.

Working with hunters from Maniitsoq, researchers from Pinngortitaleriffik - the Greenland Institute of Natural Resources managed to tag two live porpoises with satellite transmitters. This is the first time in Greenland, and as far as we know the first time anywhere, that researchers have succeeded in actively driving porpoises into nets to capture them alive.

Harbour Porpoises are among the world's smallest whales and are widely distributed throughout colder coastal regions in the Northern Hemisphere. They are very sensitive and can die of stress when there are hauled out of the water and handled in a boat. So it was with considerable trepidation that researchers from Pinngortitaleriffik, in collaboration with Jonas Teilmann (Aarhus University) and hunters Svend and Knud Heilmann from Maniitsoq initiated a pilot project to clarify whether it was even possible to catch live porpoises and attach satellite transmitters to them. The pilot project, which received funding from IIN, Ilinniartitaanermut Ilisimatusarnermullu Naalakkersuisoqarfik – the Department of Education and Research, was an important step in the run-up to the launching of an even larger project, which involves tagging numerous porpoises.

The goal is to map the porpoises' migration and diving behaviour in West Greenlandic waters, and to gather information on the porpoises' feeding areas and their role in the marine food chain in the seas west of Greenland.

Hunters can tag the animals themselves

All in all, the project has been a successful operation that provides solid background knowledge for future porpoise tagging programs in West Greenland with the help of local labour.

"Over the long term, it would be a good idea to outsource the work so hunters could catch and tag porpoises on their own. The weather has been a highly decisive factor and a good deal of time has been wasted waiting for good weather. The wind has to be under 5m/sec., there can't be any swell and the animals can be most easily spotted if the sky is slightly overcast.
"If the hunters are given this job, it could fit in with their other work, allowing animals only to be tagged when conditions are ideal. The hunters' dinghy, a Nuummit 19 with a 150 hp outboard motor, is an obvious choice for this type of work. It's fast and has a flat working surface on deck, making it a convenient craft for working with porpoises", says senior researcher Mads Peter Heide-Jørgensen.  

New knowledge about harbour porpoises

For approx. one year, the transmitters on the animals' dorsal fins send the position and diving data to a satellite every time the porpoises break the surface of the water. It appears that the two animals have very different swimming behaviour, with 7617 remaining within the same area, while 7618 roams much further afield. The most surprising discovery is that that both animals venture far from the coast into areas with very deep water (>3000 m) and dive to depths of over 300 m.

We already know much more about porpoises than we did before. After they were released, both porpoises swam south at a speed of roughly 4 km an hour, covering approx. 150 km in 4 days. One of the porpoises crossed the Davis Strait and for number of days it was closer to Canada than to Greenland before it swam north in the middle of the Davis Strait (see map). The other porpoise also swam considerable distances, but largely remained on the outer edge of the coastal banks.

"The most surprising discovery is that that both animals venture far from the coast into areas with very deep water (>3000 m) and dive to depths of over 300 m." which is approx. 100 m deeper than the deepest dive that porpoises perform in other areas. Porpoises are found throughout the North Atlantic and are normally associated with shallow water areas close to the coasts of Europe. Now we know that in West Greenland they can also be found far from land and in deep-sea areas. An interesting question is what they eat in water that is so deep. Porpoises have a high metabolism and a very thin layer of blubber, so they are always hunting for food.

Since it's now been proven possible to capture and track live porpoises in Greenland, Pinngortitaleriffik has initiated a larger study, which aims to shed light on the porpoises' migration behaviour and living environments in Greenland, including how they use these various areas with regard to diving depths. Their migrations also provide information on important feeding areas for porpoises in Greenland, and thus on their role in the marine food chain in the seas west of Greenland.

Written by biologist Nynne Hjort Nielsen and Communication Officer Kitte Vinter-Jensen

Updated 06.06.2019