I've mentioned this before in a couple of posts, but a couple of years ago we crossed behind a trawler leaving Bate Bay and headind south around dawn. In his wake was a trail of dead fish - mainly small whiting, flathead, and bream. It was one of the saddest sights I'd ever seen off Cronulla. I've since been told by locals that they've seen pros working throughout the night in Bate Bay, especially around Wanda and Greenhills.
My money is on trawler bycatch.