Interesting fishing patterns in the Clyde Estuary. I could find the following quite interesting article about it.
The tracks seem to be similar to Purse Seine, but there are many fishing techniques used in the Clyde Estuary, and I am not a fisherman, so make your own mind up.
Here is an article from Seafood Scotland about Purse Seine.
Here are the routes of some trawlers and a fishing support vessel.