5 Ways How NOT to Kill Your Catch & Release



It is late August and you have just hooked up with a 40 plus inch northern pike on the shallow edge of the cabbage and it’s pulling very, very hard. You had just tossed a “Snaggle Tooth”, multi-treble crank bait with a light rod and light line. Water temperature is around 22 Celsius and rising. It’s taking longer than usual getting this fish in due to the light gear, and it is also pulling sideways because that crank bait has hooks in the mouth and outside on the gill plate. After several minutes the beast is slowing down and is now boat side and you are certainly stoked. “Snaggle Tooth” resembles a feral cat latched onto the face of a curious German Shepard. Claws all in.

You spend a few minutes boat side trying to rip that crank out but feel that it would be easier to lift the beast into the boat to accomplish that task. You eventually get the crank out with some minor bleeding (by the fish too). You are still stoked and quite breathless considering this is the largest fish you’ve ever landed and now you need a few photos to document the event. However, your fishing buddy has to hunt down the camera which is stashed away in a bag somewhere and it takes a few minutes to dig it out.

The camera is found and now its picture time. You hold up the fish with one hand by the gill plate, vertically. This is right after you put on a dry pair of gloves in order to get better grip on the fish so you don’t drop it.

You pose for two or three photos and set the fish down to see if the photos are okay. The pictures are fine and now it is time to get your trophy back into the water. You realise that the fish has fought hard and probably needs a helping hand with recovery. So, just like you saw on your favourite fishing show, you place the fish in the water and hold on to its tail, all the while rocking it vigorously back and forth in the water in order to get water moving past its gills to ‘revive’ the beast. You really do care that this fish survives and lives to spawn another day. After a few minutes of reviving, the fish makes a concerted burst and swims off into the depths.

What a day! You finally landed that master angler northern pike, had a great fight, got some awesome photos, and revived that trophy fish until it ‘came back’ and swam away on its own to possibly be caught again by another lucky angler. But where did that fish swim off to? What kind shape was it really in after that battle and subsequent release? In this article I will break down this fictitious angling event and show how the cumulative impact of many different factors and sub-lethal stress scenarios can lead to a high incidence of post-release mortality. In other words, the fish that swam away to die. I am not suggesting all the fish you catch are going to swim off and die after you release them. Far from it. I simply want to explain what happens to fish physiologically in certain angling situations and how you can make a difference in the survival of your catch, armed with this knowledge.

Government agencies all across North America have simple and sometimes complex sets of angling regulations in place in order to manage fish populations in a sustainable fashion. With these regulations (creel limits, slot limits and other size restrictions) regulators have made catch and release anglers out of everyone, whether they want to be or not. Therefore it is critical that we pass on all available science and knowledge to anglers so they can make the best decisions out on the water when ‘catch and release fishing’.

There are five major points I want to cover here; water temperature, tackle and gear, duration of fight, time out of water (air exposure) and the cumulative impact of these events.

Okay, let’s break this down.


1) Water temperature
This is EXTREMELY IMPORTANT! Water temperature exerts important control over most physiological processes in fish, so extremes in temperatures can be deadly. It’s typically the warm water scenario which can play a negative role in the catch and release process. Warmer water has less dissolved oxygen, which can complicate recovery after physical exertion. Some Atlantic Salmon angling fisheries are closed during warm water periods to avoid excessive mortalities in catch and release situations. Warmer water has already put this fish in a potential oxygen debt situation, depending on the amount of physical exercise that is about to take place.

2) Tackle and Gear
This is where it starts. The multiple treble hooks of “Snaggle Tooth” are impressive and effective. However, the removal of those hooks (especially barbed) can add minutes to an already stressed fish from the physiological disturbances of the fight. This is especially critical if the fish is out of the water for an extended time because of the length of time it takes to remove the lure. Subsequent wounds left behind can invite bacteria, always poised to enter and colonize an organism stressed in a warm water environment. The single biggest consequence of using a line and rod combination much to light to land large fish quickly, is exactly that. Things are building up against this beast.

3) Duration of Fight
Starting to collect a debt load. The longer the fight experienced by this fish, the greater the magnitude of physiological disturbance and the length of recovery time. Some of these disturbances include accumulation of lactate, depletion of energy stores and osmoregulatory imbalances. The culmination of these disturbances is more than partially responsible for the fight coming to an end. Energy stores used up, acid base disturbances causing havoc in most basic cellular functions and enzyme activity, and oxygen depletion from heavy aerobic exercise, this fish needs some ‘down’ time to rebuild its energy stores and replenish its oxygen debt. The problem with that is that fish have really small hearts, therefore it takes longer for these physiological processes to return to ‘normal’. At this point in time of this fictitious angling event, under the environmental conditions present and after the extended fight and hook removal fiasco, the fish still has a fairly decent chance in recovering and getting back to what it does best. Feed. However, there still needs to be a round of photos.

4) Time out of Water
“Like a fish out of water”. Time out of water or air exposure, is a consequence of photo opportunities, removing hooks and measuring the size of the fish you just caught. In this case, the fish was brought to the boat to remove the hook, stayed in the boat while searching for a camera, posing for photos and waiting to see if the photos were ‘good enough’ and of course to measure the fish on the tape inside the boat. Fish basically draw oxygen from water moving across their gills. After extended air exposure the gill lamellae collapse, this leads to the adhesion of the gill filaments, which in turn leads to more physiological complications. Some of these include blood oxygen tension (oxygen bound to haemoglobin) which can fall up to 80% leading to anoxia. Cardiovascular responses (heart rate, stroke volume, cardiac output) are negatively impacted and last longer with exposure to air. Again fish have small hearts. It takes a long time for fish to replenish their oxygen debt, especially when further complicated by air exposure after vigorous exercise in warm water.

5) Cumulative Impacts
It all adds up. Individually, each one of these scenarios do put stress on fish, but through adaptive evolution fish are built to withstand them as a part of everyday life underwater. However when two or more of these physiologically altering events start to stack up, it is time to take notice.

Let’s break this down again. The water is warm. We have already established that. Once hooked up, the fish utilizes all available energy to try and escape “Snaggle Tooth”. Since the light gear is in use, the fight is extend much longer than this fish would experience naturally, resulting in acid/base changes and osmoregulatory disturbances and depleting energy reserves. This fish has physically spent itself when finally to the boat. It needs to recover. With its’ relatively small heart and low oxygen content warm water, it needs time and a safe space (deeper water to avoid flying predators) for this. A full recovery at this time is achievable. But the chances of that happening are getting slimmer. “Snaggle Tooth” needs to be removed.


With hooks all in and a short attempt at removal, the fish is pulled out of the water by its gill plate and laid on the bottom of the boat for the angler had neither net or sling. By grabbing the fish by the gill plate and lifting up, gill filaments are exposed and this adds more stress. Almost immediately the gill lamellae collapse along with the adhesion of the gill filaments. This basically turns the oxygen tap off therefore adding to the already rapid accumulation of oxygen debt. This causes further stress on cardiovascular system with changes to heart rate, stroke volume and cardiac output. “Snaggle Tooth” is removed leaving behind some nasty wounds which can come into play post release. The vertical hold of large fish like this by the gill plate can cause more than gill filament damage from air exposure. Structural corruption to the jaw area and vertebrae, internal organ and mesentery tissue damage can also occur.

Pictures need to be taken. Problem is the fish has been out of the water since it was landed and since the camera cannot be found right away, the fish spends even more time out of the water. This further contributes to the havoc and chaos that its internal physiology has been experiencing as of late. It has been six minutes out of the water. However the camera is found and photos are taken. One with the vertical one hand gill plate lift, and a couple of nice holding the tail and supporting the pectoral girdle shots, however a brand new dry cotton glove was put on for grip and removed most of the protective and functional ‘slime’ on the tail section. This ‘slime’ or mucous layer aides in gas exchange through the skin and inhibits harmful bacteria from causing problems later on.

The fish is not putting up much of a fuss anymore but it is back in the water. The reviving technique being used by vigorously pulling the fish back and forth in the water is not helping. Proper flow of water through the gills in order to ‘extract’ oxygen is only possible with flow in one direction. Front to back. Moving the fish back and forth only further complicates replenishing the already plundered oxygen debt and trying to restore physiological functions back to some kind of normal. The gills are also known to function as the principle site of body fluid pH regulation and nitrogenous waste excretion­.

After several minutes of a sincere attempt to ‘revive’ the fish, it more or less uses its last burst of energy in an effort to escape and swims off. It will naturally go to an area of depth that offers cover and perhaps cooler and hence more oxygenated water. However, it is too late for this fish. Far too much pressure has been put on its physiological systems to recover.

Post Release Mortality
The end result. Even if it did recover partially, a bacterial infection from compromising the slime layer and tissue damage from hook removal along with a depressed immune system can cause delayed mortalities. The inability to swim because of structural damage from the vertical holds that cause problems and changes to feeding behaviour or predator evasion can result post release mortalities. Delayed mortalities resulting from severe exercise and structural damage can take up to five days depending on the type and duration of damage, environmental conditions and even the species of fish. But the best thing to do is always use caution and common sense.

When Fisheries Branch conducts population monitoring and various non-lethal type fisheries programs, we always try and do them when water temperatures are less than 20 Celsius. No matter if it is a boat electro fishing survey with Silver or PIT tagging Lake Sturgeon in the Winnipeg River, conducting these studies in cooler water dramatically reduces mortalities.

I must say that I have used a drastic and dramatic example of the things you shouldn’t do when playing and handling a fish. This was so I could touch on most of the points relevant to the topic and really bang home the message of cumulative impacts. Obviously there are many different scenarios based on geography, species and even lake or river type, but with using the proper techniques every time you fish, will cover anything you come up against.

But my best advice is to use the cautionary approach. Use the recommended handling techniques on all fish, regardless of species or location and delayed mortalities will be reduced. Do your research and pay attention to your surroundings and situations. Get to know your species you fish for and what some of the temperature tolerances for them are. Treat the fish you hunt with respect when catch and release fishing, and they will treat you well back.


About Author

Ken has recently retired from a 30+ year career in fisheries research and management conducted all across Manitoba. From the Theliwaza and Lower Nelson Rivers, to Manitoba’s Parkland and Whiteshell areas, Ken has worked tirelessly in efforts to improve fish populations and recreational angling opportunities through science and common sense based realities. A rabid fisher himself, with a penchant for tossing flies at rather large salmonids, Ken hopes to share his knowledge with all Hooked Magazine readers through the unique combination of biologist and angler.

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