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Improving Survival For Catch And Release Fish? No More Than 10 Seconds Air Time For Removing Hook
Posted on Friday, January 15, 2016 (PST)

Ten seconds is all the time an angler should take to remove the hook, take pictures and return a fish to water, according to a recommendation in a recent survey of studies about the impacts of exposing fish to air.


While the length of time of recommended exposure has a lot to do with the condition of the fish, as well as the temperature of the air and water, air exposure has a significant impact on post release survival and behavior, the study says


Air exposure causes inadequate oxygenation of the blood, known as hypoxia, and damages the gill lamellae, causing physiological stress and physical damage in the fish that increases with the time the fish is exposed to air, the study says.


“Our review outlines how extreme care needs to be taken to reduce air exposure when the landed fish is exhausted, water temperatures are beyond the normal range, or with known sensitive species,” Katrina Cook said. She is a PhD student in the Pacific Salmon Ecology and Conservation Laboratory at the University of British Columbia in Vancouver, BC.


As simple as this may sound, catch and release fishing regulations seldom require a precise release procedure that would require a limited exposure to the air, even though air exposure duration is an easy metric to measure and enforce.


“However, with the appropriate tools, there is little need for air exposure at all for unhooking and releasing or even measuring and photographing the fish,” Cook said. “To meet the 10 second target, or even eliminate air exposure all together, fish should be hooked superficially in the jaw, not played to or beyond exhaustion, and unhooked while submerged in a knotless mesh net.” 


Longer exposure to air often occurs when a hook is deeply lodged in the fish, but this can be avoided with the use of tackle appropriate for the target species.


“The bait and hook types that are best for the welfare of the fish will depend on the target species,” Cook said.  “Generally, however, single barbless circle hooks (if using organic bait) and artificial lures, especially artificial flies, typically result in superficial hooking, short handling times, and limited tissue damage, which will all reduce air exposure.”


In addition, Cook recommended using lines of appropriate breaking strength so to not excessively exhaust the fish. 


When a fish is removed from water, the study says, “a cascade of physical and physiological disturbances supervene.”


-- damaged gill lamellae, which are responsible for gas exchange, collapse, gas exchange with capillaries and aerobic respiration stops;

-- the fish develops an oxygen debt, carbon dioxide (acidic) accumulates and combined with the lactic acid developed during anaerobic exercise, blood pH drops;

-- the heart rate slows until the fish is returned to the water. At that point, the heart becomes tachycardic and the longer the fish is exposed to air, the longer the heart disturbances occur.


These stress responses can be cumulative. In fact, air exposure is just one issue for a fish that has been hooked or netted: injuries, exercise and environmental conditions also cause stress that are only exacerbated by air exposure, according to the study.


“In fisheries where fish ‘fight’ to exhaustion burst swimming and the resulting power output from locomotory muscles, fueled by anaerobic metabolism, depletes tissue energy stores and initiates a stress response,” the study says.


Rainbow trout mortality has been shown to be highest from air exposure when the trout has struggled to escape. Survival is higher for fish that remain calm.


Temperature is important, the study says. Bringing a fish up from cooler water depths to a warmer surface can cause thermal shock. Summer water temperatures regularly approach critical temperature thresholds “beyond which only passive anaerobic metabolism is possible, a phenomenon that will increase as the climate warms,” the study says.


Air exposure can have other affects, as well. A study of Atlantic salmon found that fish not exposed to air – presumably also not exposed to a fight for their life – produced twice as many offspring as fish exposed up to 10 seconds and three times as many offspring as those exposed for more than 10 seconds.


The survey of literature about fish and exposure to air, “Fish out of water: how much air is too much?” was published online in the journal Fisheries


Cook’s co-authors are Robert Lennox, a PhD student in the Fish Ecology and Conservation Physiology Laboratory at Carleton University in Ottawa, Ontario; Scott Hinch, professor of Fisheries Conservation at the University of British Columbia and leader of the Pacific Salmon Ecology and Conservation Laboratory; Steve Cooke, professor of Environmental Science and Biology at Carleton University and leader of the Fish Ecology and Conservation Physiology Laboratory.


Fish exposed to air during commercial fishing operations is more complicated, more difficult to avoid and more often gear dependent, Cook said, but overall the 10 second rule sticks.


There are a number of “interacting factors” at play during capture and handling.  While air exposure is a good way to measure fish behavior, other stressors should also be assessed to determine “the severity of the capture event,” she said.


“Gillnet capture often results in severe injuries which can have lasting effects and will act as a cumulative stressor in addition to air exposure,” she said.  “Therefore, as with any fish-capture scenario, probability of survival following gillnet release will be improved if air exposure can be reduced or eliminated.”


She went on to say that with severely impaired fish, “on-board facilitated recovery has shown promise in improving survival.”


Still, reducing air exposure to less than 10 seconds during commercial fishing is difficult and would require changing methods or gear, the study says.


“Where air exposure cannot be minimized, regulatory agencies should consider the argument of whether it is ethical to release captured fish,” the study says. “If a fish suffers physiological or physical trauma from which recovery is unlikely, harvesting the fish may be the more appropriate action.”


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