Cage fighting?

This is Santa Luzia, Portugal, apparently the Octopus Capital……. (of Portugal? The world?)!

Not being au fait with fishing practice around the world, I am intrigued by the cages on these fishing boats - is it to stop would be escapee octopi (octopuses) or to stop unsteady fisherman falling into the drink?
Large

If you know the answer , please let me know.