'Rare' three-clawed crab caught in Peel Inlet

A Mandurah family was left "a little shocked" when they hauled in a rare sight while crabbing last month.

Haydee Carman and her family were out on the boat in the Peel Inlet when their nets snared a crab boasting an extra claw.

"We were just kind of stunned, it's not every day you come across that," Ms Carman said.

"He was sized and healthy but we thought we'd release him and maybe let someone else have a chance to catch him."

Department of Primary Industries and Regional Development crab research scientist David Harris said it was uncommon, but not unheard of, to spot a three-clawed crab.

"[It's] rare, but not unheard of," he said.

"The mutation represents part of the natural genetic variance in crab populations and usually doesn't appear to have a negative effect on the animal, which would appear to be the case here as the crab looks healthy, has excellent colour, and is a reasonable size.

"We occasionally come across crabs with genetic mutations that have affected their claws such as this during our monitoring surveys, and receive the odd report of this from the general public."