Satellitetagging

of Harbour porpoises

Harbour porpoises are shy animals and can be difficult to track. The only really effective way to study the life of a porpoise, is by tagging it with a tracking system. These different tags can measure the behavior and movement of the animal and then transmit these informations either by satellite or by saving the data on the unit. It is difficult to capture a porpoise, and it is therefor important to collaborate with the lokal gill net fishermen. It happens now and then, that a porpoise get trapped in the nets, where they are captured and we are able to tag them before releasing them back into the wild. Since 1997 we have monitored the movement and diving behavior of harbour porpoises together with The University of Southern Denmark, The University of Kiel, Technical University og Denmark and Fjord&Bælt in Kerteminde.

The porpoise is tagged on board the ship, by mounting a tag on its dorsal fin. This process takes up to 30 minutes and while mounting the tag, we do blood samples for further health investigations. The satellite tags starts sending information right after the release, and when the tag falls of, it is often lost for good, but sometimes we find them, and if you ever fin one, we are very interested in getting them back, and will pay a finders fee.

Project 1997-2001

From the data provided to us from the satellite tags, we can se that some of the porpoises travel far, some of the animals even go from the inner danish waters, along the coast of Norway and then crossing the North sea to England, but the majority of the seksual mature porpoises are staying within a more limited area like the inner danish waters. 

Maximum daily diving depth collected from 16 tagged animals between 1997-2001
The map is showing the movement of porpoise no. 4. It was tagged on the 8.th of november 2000, in Kerteminde. The arrows point in the porpoise swimming direktion.
Showing the mean porpoise diving time based on information from 43.000 dives.

Diving behaviour

The harbour porpoise often dive to the seabed which is also the location of many fish species.

Depth:

  • The harbour porpoise prefer to be at a depth less than 40 meters.
  • The maximum depth was measured in Skagerak at 200 meters

Activity:

  • No change in diving activity between night and day.

Diving time:

  • Maximum time is 10 minuts
  • Most frequent dive length is 1-2 minutter

Due to a higher amount of red blood cells in the blood and muscles of the harbour porpoises, it can hold it's breath longer than humans. But it still have to surface for air frequently. These blood cells trap the oxygen when it breathes, and storage it for later use. This storage of oxygen ecxeeds the one of humans, and this is why the porpoise can be submerged for a longer period of time. Also the porpoise can shut down the use of some organs by contracting arteries and limit blood flow, then only the heart, brain and muscles get new oxygen during a long dive.

Why do we tag porpoises?

To be able to study:

  • Seasonal movementpaterns
  • Their preferred habitat areas
  • Diving behavior
  • Differences between gender and age
  • Healthstatus
  • Echolocation and foraging
  • Bycatch

Publications

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A harbour porpoise is tagged, in Boring Vig 2018, with a VHF transmitter that can measure heart rate and more. Photos by Esteban Iglesias Rivas