The surfing seal was spotted by one of the Swedish Coast Guard's reconnaissance vehicles as it flew over the bay in mid-July.
"When the Coast Guard flight passed Hanö Bay last week, the camera caught sight of this seal surfing. A real summer pro!" the agency wrote on its Instagram page.
"While the seal is enjoying the waves, we would like to take this opportunity to remind you: mark life jackets and other flotation devices with your name and phone number. If they are found drifting, we can call you and ask if everything is okay, or tell you that we suspect a seal has borrowed your board."
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The agency's press spokesperson Valdemar Lindekrantz told P4 Blekinge that the coastguard often spotted both seals and abandoned surfboards and widsurf boards, but had never to his knowledge observed them together.
"In my eleven years at the coastguard, I've never seen anything like it," he said.
He said the aircraft had zoomed in on the board to check that no one was in trouble.
"When they zoomed in, they saw that there was a seal lying there, and that it had taken over the board and was surfing on it instead," he said.
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