When we release a fish, either as the target of catch and release fishing, as returned bycatch, 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.
We all know the rule, air and fish just don’t mix. While for the angler, the sweet smell of the ocean and mountain air conjures fond memories of long anticipated adventures, our fishy friends have not evolved to enjoy the breeze. 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 increases a fish’s chance to live another day, but why is it exactly that extended air exposure and longer fight times are bad news for fish?
In addition to catching it’s breath, to successfully survive once returned to the water, a fish may also need to tick a range of other boxes. 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 organization 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 meter 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.
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, took 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, there is evidence to suggest that released fish also exhibit behaviors 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. So 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;
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, away from 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 released fish the best possible chance of survival.
Another great example of how the latest recreational fishing research can help benefit fish and fishers alike.
For more information:
Impacts of dissolved oxygen on the behavior and physiology of bonefish: Implications for live-release angling tournaments
Physiological disturbance and recovery dynamics of bonefish (Albula vulpes), a tropical marine fish, in response to variable exercise and exposure to air.
Refuge-Seeking Impairments Mirror Metabolic Recovery Following Fisheries-Related Stressors in the Spanish Flag Snapper (Lutjanus carponotatus) on the Great Barrier Reef.