THE Australian Maritime Safety Authority was investigating the latest sighting of a shipping container floating off the Sunshine Coast.

But that's not the only concern for Mooloolaba's fishing fleet which is reporting a large increase in sharks of all species with one spanner crab operator reporting tiger sharks had tried to pull pots from his hands.

Warnings were issued yesterday of the shipping container hazard after an earlier sighting saw the Mooloolaba Harbour's commercial fishing fleet put on high alert.

The Maritime Safety Authority was now investigating whether a sighting by commercial spanner crab fisher Shane Underhill at 5pm yesterday was the same container.

Mr Underhill said he had received a warning while at sea from the harbour dock facility he uses to unload that there was a hazard floating off Mooloolaba.

At around 5pm he came across a large shipping container, sitting high in the water and bobbing about wildly which he thought indicated it was probably empty.

"I went past it on the way home," Mr Underhill said.

"It wouldn't be much fun to run into it. Even at a slow speed the way it was bobbing up and down it could do a lot of damage. It's a bit of a worry."

Mr Underhill said the commercial fishing fleet had enough to worry about with a significant increase in numbers of all types of sharks off the Sunshine Coast.

Bull sharks were everywhere, he said, but tiger sharks were particularly aggressive.

"We're losing gear left, right and centre," Mr Underhill said.

"It's starting to get frustrating. It's crazy at the moment. There will be 20 to 30 sharks behind the boat when I'm cleaning up.

"Tiger sharks are not afraid of the boat. They come right up and I've had them try to pull pots out of my hands."