Do fish survive catch-and-release?
We release fish for a variety of reasons. It feels great to let a fish go, and know that you can have all the fun of fishing without killing. But mostly it is about a sense of responsibility for the health of the ocean and the future of the fishery. We release fish because we want them to live.
So, do they live? And what are the factors that determine their chances of surviving after being released?
We pulled together a range of recent studies on the subject from around the world, and looked at what factors affect post-release survival of fish. Fortunately scientists have done a bunch of work in New Zealand too.
While surviving the catch-and-release process may vary from species to species, it appears that in certain conditions, with good gear and handling practices and in shallow water, snapper may be considered pretty resilient. However, like other species, they may be affected by the experience—reduced energy, bleeding and impairment that affects their long-term contribution to the gene pool in unknown ways.
Depth
Snapper can display subtle signs of barotrauma in water as shallow as 11 metres, but actual death related to barotrauma is pretty low (less than 4%) in water less than 30 metres deep. But in water deeper than 30 metres mortality increases rapidly—up to 20 times higher (69% died in one study).
Venting reduces mortality in some species, but it hasn’t actually been proven to be effective with snapper. A study of ‘re-pressurising’ snapper showed a surprisingly high survival rate of snapper even from depths greater than 50m, which indicates that descending devices might have an application here in New Zealand.
You can catch and release kingfish in deep water all day and they will suffer little ill effects if mouth-hooked, because they can vent their swim bladders. On the flip-side, just about every hāpuku you bring up to the boat is a dead hāpuku.
Hooks
In shallow water, mortality is low (less than 3%) for mouth-hooked fish and high (greater than 50%) for gut-hooked fish. Circle hooks are worth the switch, as they tend to hook fish in the corner of their mouths, as opposed to J-hooks which present a greater risk of gut-hooking fish.
Similarly fish are less likely to swallow artificial baits like jigs and soft-plastics, and are more likely to swallow natural baits.
Other factors
Cooler water and air temperature can result in less mortality than in warmer conditions, suggesting that catch and release is better for fish in winter than in summer.
Clearly the less exhausted a fish is when released, the greater chance it has of surviving. So quickly landing fish using heavy drags and strong gear reduces the risk of exhaustion which can result from a long fight.
While out of the water, the fish is suffocating, and the drying of gill membranes is causing damage. Keeping the fish in the net in the water after the fight can help it to recover and better deal with the stress of suffocation when you take it out of the water to remove the hook and take a photo. Using de-barbed hooks will reduce time out of water, and limit damage to the fish (and crew).
When people ask me how long is too long for handling the fish on the surface, I suggest they hold their breath lifting the fish out of the water… and put the fish back when they can’t hold their breath any longer!
Can catch and release help the fishery?
A study from South Africa showed that ‘low-intensity’ catch-and-release fishing did not have a negative impact on protected fish populations, which opens up the possibility that release-only zones could be established as protection measures for specific areas, specific species of fish, specific parts of the season or important classes of fish.
Some of the greatest fisheries globally, and indeed in New Zealand, use some form of strategic release as a means to keep marine ecology healthy, while still allowing fishos to fish and enjoy those areas, so it’s worth exploring further.
If you want to know more, or want to see all of the studies we referenced, check out the full literature review.
