The physiological effects of angling stress on fishes

Bobbers in a pond (Image taken by Krystal Pocock)

Have you ever been catch-and-release fishing and found yourself wondering if the fishes you catch go on to live healthy, productive lives after you toss them back? Maybe you’ve contemplated how long it takes for the puncture mark left by your hook to heal or how removing fishes from the water for short periods of time affects them. If these thoughts have ever crossed your mind, you’re not alone. In fact, there has been a lot of research completed on the subject.  Studies have shown that catch-and-release fishing is one of the biggest sources of stress to game fishes (Meka & Mc Cormick 2004; Twardel et al., 2018). When a fish is exposed to extremely high amounts of stress, hormones that are produced by the stress response can be fatal. Luckily, complex processes in the body work to regulate hormone levels and are typically able to quickly return the body to its normal state before stress hormones are fatal. More often, angling-induced stress tends to have what is called sub-lethal effects, which cause other important functions in the body to slow down or stop altogether. As such, recovery from elevated stress levels in captured fishes requires a lot of energy and often causes energy to be taken away from other important functions like reproduction and survival to compensate (Meka & McCormick 2004).

Imagine you’re out fishing on a beautiful day and you’ve finally gotten a bite. What happens next can directly contribute to the amount of physiological stress that a fish experiences during catch-and-release angling. There are three major sources of stress and potential contributors to mortality that fish are exposed to while being captured: exhaustion from the reeling and landing process (i.e., the amount of time that it takes an angler to successfully remove the fish from the water), injuries from hooks, and air exposure (Meka & McCormick 2004). Just like humans, fishes can become extremely tired from too much exercise and the exercise fish get while an angler attempts to reel them in can be physically exhausting. If a fish has not fully recovered from reeling and landing exercise once they are returned to the water or quickly thereafter, they can easily be eaten by a larger fish (Meka & McCormick 2004; Twardek et al., 2018). Additionally, injuries obtained from hooks during the angling process can be deep and cause a lot of bleeding, which can cause death or infection (Meka & McCormick 2004). Furthermore, the longer that a fish is out of water and exposed to air, the more stressed they become (Meka & McCormick 2004; Ferguson & Tufts 1992). When fish cannot pass water over their gills to obtain oxygen, they start breathing very quickly, which causes a lot of carbon dioxide to accumulate in their bodies. Once there is excess carbon dioxide in their blood, fishes have a hard time retaining oxygen and can die if they aren’t able to obtain enough oxygen (Ferguson & Tufts 1992). Thus, exhaustion, injuries, and air exposure all have the potential to cause mortality, however, this is rare and typically happens under extreme circumstances.

More often, angling stressors such as those discussed above have sublethal impacts on fishes due to stress causing disruption of other important functions to compensate for the energy needed to recover (Meka & McCormick 2004). For example, sublethal impacts of stress associated with catch-and-release fishing are reduced reproductive output, reduced growth and time spent foraging, reduced immune response, and altered migration behaviors (Meka & McCormick 2004; Twardek et al., 2018). Additionally, research has shown that fish become more stressed as landing time, air exposure, and the time it takes to remove a hook increases. Fish are also more stressed when water temperatures are high (Meka & McCormick 2004). Furthermore, the longer fish are exposed to air, the longer it takes them to move again once they’ve been tossed back into the water (Twardek et al., 2018). One study even suggested that when fish are stressed, it can take as long as a day for stress levels to return to normal (Meka & McCormick 2004)!

Minimizing the time a fish is held outside of water, exposed to air, can greatly minimize the amount of capture stress (Meka & McCormick 2004; Photograph taken by Krystal Pocock).

Luckily, there are some best practices that anglers can utilize to reduce the amount of physiological stress that fish experience from catch-and release fishing. For example, using barbless hooks reduces injury during capture and use of natural bait can reduce injuries obtained from fish swallowing large, plastic lures (Brownscombe et al., 2017). Taking care to reduce the amount of time it takes to reel the fish in and time spent handling the fish out of water can also reduce stress. Finally, using specialized tools to remove hooks or cutting and leaving the hook in if it is found in a sensitive spot can reduce stress associated with angling (Brownscombe et al., 2017). Using smart angling practices can reduce stress and mortality associated with catch-and-release fishing and help ensure that there are future populations of fishes for years to come.

Brownscombe JW, Danylchuk AJ, Chapman JM, Gutowsky LFG, Cooke SJ (2017) Best practices for catch-and-release recreational fisheries- angling tools and tactics. Fisheries Research 186:693-705.

Ferguson RA, Tufts BL (1992) Physiological effects of brief air exposure in exhaustively exercised rainbow trout (Oncorhynchus mykiss): Implications for “catch and release” fisheries. Canadian Journal of Fisheries and Aquatic Sciences 49:1157-1162.

Meka JM, McCormick SD (2005) Physiological response of wild rainbow trout to angling: impact of angling on duration, fish size, body condition, and temperature. Fisheries Research 72(2,3): 311-322.

Twardek WM, Gagne TO, Elmer LK, Cooke SJ, Beere MC, Danylchuk AJ (2018) Consequences of catch-and-release angling on the physiology, behavior, and survival of wild steelhead Oncorhynchusm mykiss in the Bulkley River, British Columbia. Fisheries Research 206:235-246.

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