"I pulled up the lobster pot as usual and there it was. It had tried to get into the cage but hadn't managed completely," Olsson told the local P4 Väst radio station.
The lobster is 46 centimetres long, with 28 centimetre claws.
Olsson said he does not plan to eat the lobster. Instead, he will try to arrange for it to be displayed in an aquarium so that locals can get a look.