Most of us likely release more fish than we keep. Whether we need to release fish because they are under-sized, or because we do not wish to keep them, it is important that we do what we can to maximise their chances of survival.
Much research has been conducted in Australia and overseas, and in almost every instance, the following actions will improve a fish's recovery and survival after its release:
Remove hooks from the fish's mouth
If the fish has swallowed the hook, cut the line as close to the fish's mouth as possible
Keep the fish wet and air exposure to a minimum
Use landing nets without knotted mesh (knotless silicone nets or Environets are available at most tackle retailers)
Use appropriately sized hooks for fish you are targeting (e.g. hooks that you would not expect your target species to swallow easily)
Support the body of the fish if you are lifting/holding it up - be mindful to wet your hands before touching the fish
If keeping fish in a livewell, make sure the water quality (and temperature) are maintained at suitable levels
Of course, there are some exceptions to these guidelines, and some instances where extra actions are required. Those are explained below.
Using a knotless net, supporting the fish's body, and keeping it wet all helped this little Brown Trout swim away with the best chance of survival. See you next time! (Photo credit: Owen Li)
Dangerous or unknown fish
Many of the fish we throw back are deemed dangerous, unwanted, or are simply unknown. We should never kill a fish unless we wish to keep it, or if it is a noxious species (e.g. carp or tilapia). Every species in the aquatic ecosystem has a role to play, whether that species is edible/desirable to us or not.
If you are not sure about what the fish is, or how to handle it safely, please cut the line as close to the fish's mouth as you are comfortable getting and allow the fish to fall back into the water. There is no need to endanger yourself.
Even "ooglies" need love. A pair of lip-grips, long-nosed pliers, and a little care, were used to release this venomous Stonefish safely. (Photo credit: Ben Diggles)
Fish caught in deep water
Sometimes, we are fishing in deep water (>10m), and catch fish that must be returned, either because they are under-sized, or because they are inedible or dangerous. Many fish caught in water greater than 10m in depth experience barotrauma.
Barotrauma is a condition caused by gases within a fish expanding rapidly as it is brought to the surface. At 10m, fish are experiencing twice the pressure we feel at the water's surface, at 20m, that pressure is three times that of the surface, and at 40m, that pressure is 4 times that of the surface etc. Fish with swim bladders control their buoyancy by filling those swim bladders with gases. Because of the pressure exerted on them by the water, those fish at greater depths need a larger amount of gas in their swim bladders to stay buoyant. While fish can regulate these gases (some better than others), that process takes time - much more time than it takes for fishers to wind them up to the surface.
When fish with swim bladders are brought to the surface faster than they can reduce their internal pressure, their swim bladders inflate rapidly and crush their internal organs. The more visible signs include bulging eyes, and stomachs, stomachs protruding from mouths, or intestines prolapsing from anuses.
While all of the fish handling guidelines still apply, fish hooked at depth also need to be returned to an appropriate depth as soon as possible to maximise their survival.
One of the least invasive and easiest methods is 'shot-lining' using a 'release weight' developed by Recfish West. If you cannot buy one, the NSW Department of Primary Industries has provided instructions for making your own using a large barbless hook, a large sinker, a few cable ties, and some venetian cord.
'Venting' a fish, where a hypodermic needle is used to release the trapped gases from a fish's abdomen can also help. This video demonstrating how fish caught in deep water can be released was produced by Queensland Fisheries.
Please do remember however, that not all those fish caught in deep waters release well, and even careful release techniques only increase the chances of survival, not ensure it. Some species, like Fingermark/Golden Snapper are particularly vulnerable, and are very unlikely to survive if they are caught at anything greater than 10m of depth. At 2:27 minutes, the linked video reminds us that the marine environment is a dangerous place, and fish that might have recovered over days in a safe environment, might never get the chance.
Sometimes, we as fishers must make hard choices, and fishing in deep waters is one of those instances. There is always the temptation to return small, but legal fish in the hope of catching a bag limit of larger fish, or just to continue practicing catch and release because the fish are biting. In deep waters, these actions might have more significant impacts than we appreciate. Sometimes, it is the more responsible choice to move on after catching enough for a feed and fish for something else.
The bulging eyes of this Harlequin caught in 25m of water are a clear sign of barotrauma (Photo credit: Andrew Matthews)
Catch and release study on Yellowfin Bream and Mulloway conducted by P.A. Butcher, M.K. Broadhurst, D. Reynolds, D.D. Reid, and C.A. Gray
NSW DPI catch and release handbook (salt and freshwater), which includes results from the studies informing the recommended best practices.
"Gently Does It" information brochure about the survival rates of Pink Snapper and Bream hooked shallow (in the mouth), and deeply (in the stomach/gut) produced by Infofish, in partnership with the FRDC, NSW DPI, NSW Recreational Fishing Trusts, Recfish Australia, the state of Victoria, and the Australian National Sportfishing Association
Report for the FRDC funded study "Maximising survival of released undersized west coast reef fish" conducted by R. Lenanton and J. St John
Report for the FRDC funded study "National Strategy for the survival of released line-caught fish: Maximising post-release survival in in line-caught flathead taken in sheltered coastal waters" conducted by J.M. Lyle, I.W. Brown, N.A. Moltschaniwskyj, and W. Sawynok
Report for the FRDC funded study "National strategy for the survival of released line-caught fish: tropical reef species" conducted by I.W. Brown, W.D. Sumpton, M. McLennan, D.J. Welch, J. Kirkwood, A. Butcher, A. Mapleston, D. Mayer, G. Begg, M. Campbell, I. Halliday and W. Sawynok
A Pink Snapper specific webpage including information on barotrauma, hook patterns, how to avoid deep hooking, hooking mortality associated with deep hooking, the negative aspects of prolonged fight times, correct handling of fish intended for release, humane dispatch of fish, and tips on how to maximise the food value of any fish retained. The webpage was authored by P. Hardy-Smith and J. Daly