Hi:
Finally a topic that I can legitimately declare that I am an expert.

As an ex NMFS Fisheries Observer I spent several years in the 1980s and
early 90s calculating species composition, total catch weight, and a
bunch of other stuff on a variety of vessels and fisheries along the
west coast, North Pacific, and Bering Sea. I was basically a sea going
fish accountant.

So to answer your question ya gotta consider a few conditions:

Length of Vessel
Type of gear used (Longline, pot, midwater, drag, gillnet, purse,
trawl, troll, surimi MS etc...
Target species (salmon, pollock, Cod, hake, crab)

So how do you estimate catch size? Depends on a lot of factors. Are you
talking about 100 MT midwater bag of pollock sitting on the trawl deck
of a 360' factory trawler (F/T) bouncing around the Bering Sea on a
typical January day with 50 k wind and 30' seas or a 38 pound king
salmon getting landed on a sweet little 32' double ended salmon
troller built in 1932 and planked with Port Orford Cedar?

Chris