This isn't "rec", but it is "boats.electronics".

I am wondering how the weight of a catch on a fishing trawler could be
measured while the vessel is at sea. I'm thinking that the weight of the
whole vessel might need to be taken into account as there will be variables
such as fuel, water, etc.

Anyone know how this would be done?

Maybe rather than weighing while in the hold it would be weighed in the net
before dumping into the hold?

Thanks,

Dave