Maximising survival rates of released fish

Today’s anglers and boaters have never been more aware and pro-active about protecting the environment and their beloved fishing resource. We adhere to bag and size limits, release more fish than we have done in the past, and our top fish-tagging programs prove we’re a great asset to research and science.

To that end, Recfishing Research went on a fishing expedition and fact-finding mission to see how we could maximise the survival rates of the fish we set free to fight another day. This mightn’t seem like rocket science, but it’s put together some great advice all the same.

When we release a fish, either as the target of catch-and-release fishing, as returned by-catch, or to comply with fishing regulations, the sight of it swimming away gives us a sense of reassurance that the fish has successfully recovered to see another day.

However, recent studies into the effect of extended air exposure and fight time on post-release survival rates have found that swimming away from its encounter with us is not necessarily the end story for the fish, reports Recfishing Research.

AIR AND FISH DON’T MIX
We all know the rule, air and fish don’t mix. Understanding this, anglers generally try to reduce stress in the fish they plan to release by minimising fight time and returning the fish to the water as soon as possible. This simple act increases a fish’s chance to live another day, but why are extended air exposure and longer fight times bad news for fish?

To successfully survive once returned to the water, a fish must tick a range of boxes. Besides catching its breath, this includes finding its bearings, returning to suitable depths and seeking refuge.

Most importantly, a released fish needs to regain cognitive recognition of its surroundings by drawing on its functional memory to make decisions that will help it avoid being eaten by a predator.

Depending on the experience and organisation of the angler, as well as the equipment they use, the post-capture scenario for a fish can be likened to an athlete running a 100-metre sprint and then having to hold their breath once they cross the finish line.

As a fish fights on the end of a line, its metabolic rate, response hormones and lactic acid levels rise significantly. These factors restrict the fish’s ability to replace the oxygen it is using as its muscles power it through the water.

Even before the fish is landed, the oxygen in its body may have dropped to very low levels. When the fish if removed from the water, it is often exposed to an additional period of oxygen-deprivation… while the angler unhooks, measures and records the capture.

RELEASED FISH PRONE TO PREDATION
Studies on Spanish flag snapper (Lutjanus carponotatus) in the Great Barrier Reef and Bonefish (Albula vulpes) on the sand flats of the Bahamas have found that increased air exposure and fight time significantly alters a fish's natural behaviour.

Importantly, the studies identified that, for up to 30 minutes following release, fish are significantly more susceptible to predation.

Snapper that were ‘exercised’ and then exposed to air were said to take up to 70 times longer to respond to predatory stimuli and find refuge. Even once the fish successfully identified a refuge, they were often apprehensive about entering it to obtain protection.

In addition to failing to evade predators, released fish could also adopt behaviours that actively attract predators. For example, exhausted bonefish were not able to maintain equilibrium and swam erratically, attracting higher levels of shark predation.

Studies such as these highlight the benefits of angling and releasing fish as quickly as possible, and that the biggest threat to fish immediately following release is not suffocation but… predation.

TOP 4 FISH SURVIVAL TIPS
Here’s what can anglers do to increase the survival chances of the fish they are about to release
>> Reduce the fight time by using heavy gear. Modern rod, reel and line technology provides options for anglers to use high quality, lightweight equipment that can simultaneously enable delicate presentations while keeping fight time to a minimum.
>> Assess the fish’s reflexes once brought to the surface. This can be done by looking at body tone and tail grab response. If there is little or no response, and the fish appears weak, consider whether the fish is a suitable candidate for release. If release is mandatory, then take steps to reduce further impacts.
>> Minimise out-of-water handling and air exposure time.
>> Reassess the need to take photos /admire the caught fish for an extended period of time.

LIVEWELL, LIVE WELL
In addition, studies have shown that keeping a fish in a suitably sized circulated livewell with freshwater pickup for up to 30 minutes may allow it to recover physiologically and cognitively… and lessen the risk of predation.

By adopting best practice fish-handling-and-release techniques that take account of contemporary research into post-release fish physiology and behaviour, anglers can give their beloved fish the best fighting chance of survival.

This article was reprinted with thanks from Recfishing Research.

Photo Credit: Opening Photo of a snapper by VR Fish.