Mr Williams, who was diving off Flinders Island, captured a 1.24 kilogram greenlip abalone on Thursday as the first month of the abalone season drew to a close.

The abalone's shell length was 243 millimetres, making the gigantic shellfish the largest Mr Williams had caught in his eight years of diving "by a long way".

"It was pretty amazing," he said.

"There were other large abs around it, and this one was in amongst them.

"It was just amazingly bigger than all the other abs, it made them all look like smarties.

"(On my way up) I picked it out the bag a couple times just to look at it."

Mr Williams said as the abalone was captured at the time of Western Abalone Processors' 30th anniversary, it was a good incentive to know it was being given to one of the company's largest buyers overseas.

"It was a good coincidence, and it is good to know it is actually going somewhere," he said.