by sandman on Thu Feb 11, 2010 3:19 am
IP:
Dave's hit on a couple of good points. In the larger tides of the sequence, gill nets only work for a small part of the tide - when the tidal stream is above a certain speed, the nets don't fish - they're basically blown flat to the seabed, rather than standing up like a wall.
I remember when gill-netting first took off, this was a problem. The guys who initially countered this with massively over-weighted and over-floated nets and who put on bigger haulers caught a lot more than those who fished smaller and lighter. Decimated the spurdog stock. Of course, in no time everyone was at it with predictable results.
And point two, hauling any fish as hard as you can from 100m is not going to do it any favours, particularly those with swim bladders. If you think about the reason divers take rest stops on ascent from 50m (I think that's the limit for sports divers and even from shallower depths on longer dives?) it's clear that rapid de-pressurisation isn't good.
Having said that, I did read about a cod tagging study that was done some time back where they lined cod and deliberately retrieved them from depth very slowly, then punctured their swim bladder with a canula, tagged them and released them. Quite a few turned up in commercial catches for some time after, so it's possible, with care, to do it. I've no idea (and the study couldn't say) what the mortality rate was from this but it had to have had some effect as at least some of the fish were caught and reported again later.
Pat
If it's not broke, don't mention it....