As a pre-note, I am not advocating ANY kind of commercial fishing, other than simple single-line single-hook fishing with a fishing pole in a person's hands.
Just to give another side to the discussion, I worked as a federal government observer on a commercial fishing longliner (and 2 dragnet boats) in the Bering Sea off Alaska last summer. Granted, this NOT swordfish, sailfish, tuna whatever they're catching down in the Gulf, this is flatfish, cod, rockfish, and pollock.
Longlining is MUCH MUCH MUCH better on bycatch than dragnetting is. On the boat I was on, in the 6 weeks we were at sea, I would say 95% of the bycatch was released alive. I'm not sure how much of that survives for long periods after being released, as there has been very little actual research into that, but most were in excellent condition when they were released. The fishermen treat bycatch with great care, because every boat has a government observer onboard, and if they don't they get very large fines (tens of thousands of dollars to hundreds of thousands of dollars, depending on the infraction, and NOAA, the governing agency, is very fine happy up there).
Most longlines are not left out for more than 18 hours, MAXIMUM. Anyone leaving lines out longer than 24-30 hours either doesn't know what they're doing, or doesn't care about the quality of the catch, and have no business being a longline fisherman. The fisherman I was with only left a line out for longer than 24 hours because of hazardous weather. Most longlines deployed while I was on the boat were only in the water for 6-8 hours, and usually came up nearly full. These were lines approximately 10,000 yards long, with a hook every yard.
When I was on the dragnet boats, there was rarely more than 1% of the entire catch that was still alive by the time the net was dragged on board. Dragnets are horrible, because they rape the bottom of the ocean, pulling up everything in its path and crushing it into one giant blob of worthless fish. Seals, dolphins, sea lions, sea turtles, birds, even whales have been caught in drag nets. The weight of sea life in each net, depending on the size of the boat, is 10 tons to 200 tons.
I'm not saying those same animals aren't caught on longlines, as they can be, but the bycatch is much lower than drag netting, it is safer for the udnerwater environment, and IF DONE CORRECTLY, is one of the more sustainable methods of fishing.
Again, I was a federal government observer on these boats, and seeing the state of the fisheries up close and personal, I believe that ALL types of fisheries need to be heavily restricted, and some completely closed, or these species of fish will soon be pushed to extinction. Several fisheries, such as pollock, are already collapsing and will be close to being considered unrecoverable in another 5-10yrs if nothing is done.
Farmed fishing is a start to help relieve pressure off wild fisheries, but I don't believe farm raised fish will ever be an economically viable replacement. It costs too much to raise fish to a size and weight that they can be sold at.
Edit: and to anyone who says that fisherman aren't to blame, that they're just earning a living, I say B.S. If not for what little government intervention there is, fisherman would catch every last fish in the ocean, no matter what it is, to sell for the almighty dollar. Unfortunately the government is getting a large amount of money from the fishing industry, and so does not put any worthwhile limits on fisheries. Fishermen themselves would NEVER voluntarily limit their catch to ensure the fishery survived, they'd just fish it out and move on to something else, until there was nothing left to fish for.
