The beluga whale was first sighted last week in waters off Finnmark – Norway’s most northerly county which borders Russia.
“We were going to put out our nets when we saw a whale swimming between the boats,” 26-year-old fisherman Joar Hesten told Norwegian public broadcaster NRK.
Fishers said the whale had repeatedly sought them out, and they spotted it had a harness on which it was apparently trying to rub off against the hulls of their boats.
After several failed attempts by the Norwegian Directorate of Fisheries, Mr Hesten was able to remove the two straps attached to the animal late on Friday.
Mr Hesten was accompanied by staff from the directorate and wore a survival suit before leaping into the icy waters near the island of Rolfsoya to try and undo the harness.
“When I was in the water, it came really close ... and I managed to reach and unfasten the front buckle,” he told NRK.
The second strap was harder to remove, but Mr Hesten eventually managed to attach a hook to it, and as the whale swam off the harness was pulled free.
The fishers recovered the harness, which had the words “Equipment of St Petersburg” labelled on it.
“This is not something any Norwegian scientist has been doing. What we think is that this may come from Russia,” said Audun Rikardsen, professor at the Department of Arctic and Marine Biology at the University of Tromso.
“If this whale has this on for a long time, then it is not good for it,” he said.
“We know that in Russia they have had domestic whales in captivity and also that some of these have apparently been released. Then they often seek out boats.”
Mr Rikardsen contacted Russian researchers who told him the beluga had nothing to do with them.
“They tell me that most likely is the Russian navy in Murmansk,” he said.
One of his colleagues in the same field agreed. “If this comes from Russia, and there is great reason to believe it, then it is not Russian scientists, but rather the navy that has done this,” said Martin Biuw of the Institute of Marine Research.
They believe the harness could be used to attach cameras or other instruments.
Both the US and Russia trained marine mammals including whales, dolphins, sea lions and seals during the Cold War, Vietnam War and the Iraq War.
In the US the Navy Marine Mammal Programme is ongoing and is based in San Diego, California. Animals are trained to detect enemy sea mines, to protect ports and to recover objects from the sea bed.
Russia has also been known to have trained underwater mammals for military purposes.
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