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The tagged halibut at a depth of eight metres.
Photo: Bjørnar Nygård
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“Fugitive” photographed at a depth of 8 metres

When diving off Austevoll, sport diver and photographer Bjørnar Nygård spotted a halibut with a green tag on its back. This was a halibut that the Institute of Marine Research had tagged and released in November 2008, to find out what happens to halibut that escape from fish farms.

By Kathrine Michalsen
The halibut was spotted to the north-east of Austevoll, at a depth of eight metres, partially buried in the sand.
“It looked very healthy and comfortable, partially buried in the sand. When it didn’t want to be watched any more, it swam off with us before disappearing in a swirl of sand,” says Bjørnar Nygård.

Simulating escape

The green tag suggests that this was one of the farmed halibut that were tagged and released in the middle of November 2008. The halibut is a second generation offspring of a wild halibut that was caught locally (Sotra/ Bjørnefjorden). It is now four years old, weighs five kilos and is 70-80 cm long.
The halibut was spotted approximately one kilometre north of where it was released three months ago. In addition, two other halibut have been caught by local fishermen. One was caught fourteen days after being released, very close to where it had been put out. The other one was caught three kilometres further north. All three of the halibut appeared to have found “good halibut locations”, i.e. areas with a sandy seabed and satisfactory access to food.

Katrine Michalsen

Let us know

The results so far suggest that the halibut spread out in the area around Austevoll, and that they don’t stay together.
This may mean that halibut which have only been fed pellets are capable of catching and eating live prey when they are released. It would be great if people who catch these halibut cut open their stomachs to see what they have eaten. It is very important for people to notify us if they re-catch a tagged halibut.
That is the only way that we can obtain new knowledge about halibut in this area. However, we ask that anyone who catches a halibut notes down the tag number and position, and if possible, re-releases the halibut. If the halibut is injured then, as we have said, it would be helpful to check its stomach contents, measure its length, identify its sex and attempt to take out the otoliths.

Can migrate

The re-catching of halibut from other areas suggests that halibut which are released in good halibut grounds stay put, but if they are released somewhere that they don’t like, they migrate back.
Halibut caught in Øygarden, but re-released in Vatlestraumen closer to Bergen, have remained where they were released. Other fish that have been recaught suggest that in particular young halibut don’t like to move far. In one case a halibut was tagged and transported to the other side of the fjord, before being re-released. Two months later it was recaught in the same location where it had been caught the first time. In other words it hadn’t liked the habitat where it was released, and had travelled a distance of 35 km, crossing a deep-water channel, just to get back “home”.

This in turn implies that halibut require, or prefer, very specific seabed conditions. Big halibut have also been recaught close to where they had been released, in particular locations. Overfishing in these locations may lead to a depletion of stocks relatively quickly. Unfortunately there are many examples of this, especially during the spawning season.
If you hear of anyone catching a tagged halibut, please contact Kathrine  (pictured).