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King crab with acoustic tag.
King crab with acoustic tag.
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Listening out for king crabs

In Porsangerfjorden in Finnmark, 26 king crabs are wandering around the sea bottom with acoustic tags fixed to their legs. 14 buoys with acoustic receiver record continuously any signals transmitted by the tagged crabs. Preliminary results indicate  that access to food and reproductive considerations govern the crabs’ movements.

By Beate Hoddevik Sunnset

Last week, the data from all of the listening buoys was extracted for analysis. The buoys were also used to collect data last year, and preliminary results show that temperature plays less of a role in the seasonal migrations of king crabs in Porsangerfjorden than in their native areas.

- In the native areas of the king crab, temperature governs migration between deep and shallow water. In Norway the king crab is an introduced species, and it has yet to fully adapt to the local environmental conditions, explains scientist Jan H. Sundet.

Varied behaviour

The aim of the project is to find out how long king crabs remain at various depths at different times of year. This will enable us to assess the impact of the king crab on flora and fauna in the areas where it has established itself. So far, results show great individual variation in both behaviour and the distance travelled by the crabs, but in general it is true to say that they are constantly moving, seeking out good areas in terms of access to food and reproductive considerations.

The acoustic tag is attached to the leg of the king crab.

The acoustic tag is attached to the leg of the king crab.

Lose their tags

One of the challenges when tagging crustaceans, such as king crabs, is that they change they shield their outer skeleton in order to grow. The acoustic transmitters are attached to the shell, and therefore becomes useless if the crab moult during the project.

- Large king crabs moult less frequently than small crabs, and in general change their shells with interval of a few years. That’s why we’ve tried to only tag large individuals, so as to receive signals from the transmitters for as long as possible, explains Sundet. Only one similar tagging experiment has been performed with king crabs, in Alaska.

Listening buoys

Listening buoys have been put out straight above them, and capture the signals from the acoustic tags on the king crabs.

Facts about Red King Crab

Latin name: Paralithodes camtschaticus
Natural Distribution: Bering Sea, Okhotsk Sea, and the North Pacific
Distribution in Barents Sea: Along coastal waters and tributaries in the southern region of the Barents Sea, at depths ranging from 5 to 400 m depending on time of year
Maximum size: Rarely exceeds 8 kg / 23 cm (carapace length in Norwegian waters)
Diet: Bottom species, plants

Red King Crab