I use non-barbed hooks and a special tool that removes the hook without having to pull and rip it out of them. On the occasion that I cannot remove a hook (because it has been swallowed too deeply), I cut the line as close to the hook as I can and let them go. Fish secrete an enzyme that will completely dissolve a metal hook within a day or two.
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Key aspects of catch and release include:
Using strong tackle, to minimise fighting times
Using needle-nosed pliers to aid unhooking
Using barbless hooks, for quick, easy hook removal and reduced handling times
Leaving fish in the water during the unhooking and release process, to avoid any handling
If fish are removed from the water for unhooking and/or a photo, key aspects of handling include:
Avoiding the use of landing nets; if landing nets must be used, specially designed catch-and-release landing nets (e.g. Environets) are used
Avoiding touching the fish with dry hands or dry surfaces (e.g. shirt fronts) or putting them down on dry surfaces (e.g. rocks, boat gunwhales, boat bottoms)
Only touching the fish with wet hands and wet surfaces (e.g. wet towel)
Avoiding hanging fish from their jaw/mouth/gills
Holding fish horizontally, and supporting large fish with a second hand under the belly
Minimising time out of the water (e.g. 20–30 seconds)
The effects of catch and release vary from species to species. A number of scientific studies have shown extremely high survival rates (97%+) (e.g. <4>) for released fish if handled correctly and particularly if caught on artificial baits such as lures. Fish caught on lures are usually hooked cleanly in the mouth, minimising injury and aiding release. Other studies have shown somewhat lower but encouragingly high survival rates for fish gut-hooked on bait if the line is cut and the fish is released without trying to remove the hook. This procedure should be followed for any gut-hooked fish intended or required to be released.
http://en.wikipedia.org/wiki/Catch_and_release