Sustainable Fishing: What 'Catch and Release' Actually Means for Fish Survival

Catch and release has become, in many fishing circles, a kind of moral shorthand. You release the fish, therefore you are a responsible angler. The rod goes back in the rack, the photo gets posted, and the fish — by implication — swims off unharmed to live a full and meaningful life and be caught again by someone else. The practice has been adopted so widely and repeated so approvingly that most anglers have stopped interrogating it.

The science, unfortunately, does not support this comfortable narrative without significant qualification. Post-release survival rates for fish vary dramatically depending on species, water temperature, fight duration, handling method, and a dozen other factors. Done well, catch and release is genuinely conservation-minded. Done carelessly, it is a ritual that makes the angler feel virtuous while potentially killing the fish slowly, out of sight, hours after it has been released.

Understanding what actually happens to a fish during capture — and what you can do to improve its chances of survival — is not optional knowledge for anyone who claims to fish sustainably.

What Happens to a Fish When You Catch It

The physiological stress a fish experiences during capture is significant and measurable. When a fish fights against a hook and line, it relies predominantly on anaerobic muscle metabolism — the same energy system humans use in a sprint. This produces lactic acid as a byproduct. In a healthy fish at rest, lactic acid is cleared from the blood relatively quickly. In a fish that has been fought to exhaustion, lactic acid levels in the blood and muscle tissue can reach concentrations that are acutely toxic.

At the same time, the stress of capture triggers a cortisol and adrenaline response that elevates heart rate, alters gill function, disrupts osmoregulation (the process by which fish maintain the correct balance of salt and water in their tissues), and suppresses immune function. None of this is immediately fatal. All of it can be, given enough cumulative stress and insufficient recovery time.

The critical point that most anglers miss is this: a fish that swims away strongly does not necessarily survive. Post-release mortality — death that occurs hours or days after the fish has been released, apparently healthy — is well documented across a wide range of species. The fish looks fine. It holds itself upright. It kicks away into the current. And then, sometime overnight, it dies in the shallows from the physiological consequences of what just happened to it.

This is not an argument against fishing. It is an argument for understanding what you are doing and managing it honestly.

Fight Time Is the Most Important Variable

If there is one change the average angler could make that would most improve post-release survival rates, it is this: use heavier tackle and fight fish faster.

This runs counter to a significant strand of fishing culture that prizes light gear because of the sporting challenge it presents. A 2 kg bream on 2 kg line is more exciting than the same fish on 6 kg line. That is true and that experience is real and valid. But a fish fought for eight minutes on light gear is in a categorically worse physiological state than a fish fought for ninety seconds on appropriate gear. The first fish may not survive. The second one almost certainly will.

There is a widespread misconception that a short, violent fight on heavy gear is harder on a fish than a long, gentle fight on light gear. The opposite is true. The fish's body does not care about the drama of the fight from an angler's perspective. It cares about how long it was in a state of acute stress and anaerobic exertion. Fight time is the variable, and fight time should be minimised.

This means matching your tackle to the fish you're targeting. Not tackle so heavy that casting is compromised or the fishing stops being enjoyable, but tackle adequate to the job of landing the fish efficiently. For catch-and-release trout fishing, for example, a 5X tippet on a 5-weight rod in open water is a very different proposition from the same tippet in a tight, snaggy stream where the fish will inevitably run you around structure for minutes. Read the water, adjust your gear, and be honest about the consequences of your tackle choices.

Air Exposure: The Thirty-Second Rule

After fight time, air exposure is the factor most directly within the angler's control and most frequently mismanaged. The guidance from fisheries researchers is consistent: minimise air exposure to thirty seconds or less wherever possible, and never exceed sixty seconds for species with known sensitivity to handling stress.

Thirty seconds sounds generous until you've watched someone take a fish out of the water, walk to the bank, ask their companion to take a photo, realise the companion has the camera on the wrong setting, wait while this is resolved, hold the fish out for the photo, realise the horizon isn't straight, retake the photo, and then walk back to the water. That sequence routinely takes two to three minutes. The fish, during this time, is experiencing hypoxia, desiccation of its gill surfaces, and elevated thermal stress if the air temperature is higher than the water temperature. These are not minor inconveniences. For a fish already compromised by capture stress, they can be fatal.

The protocol that actually works: wet your hands before touching the fish, keep it in the water while you remove the hook, prepare your camera before the fish leaves the water, lift it briefly for the photograph, and return it immediately. If you fumble the camera, the fish goes back in the water and waits. The fish's survival takes priority over the photograph.

Water Temperature and When Not to Fish

One of the most under-discussed aspects of catch and release sustainability is the role of water temperature, and it deserves more attention than it gets.

Cold-water species — trout are the obvious example, but also Atlantic salmon, Murray cod in certain conditions, and several other species — have upper thermal tolerance thresholds above which their ability to recover from capture stress is severely compromised. For brown and rainbow trout, the research is fairly clear: water temperatures above 18–20°C produce sharply elevated post-release mortality rates, even when fish are handled correctly and fight times are short.

This matters practically because Australian summer conditions can push lowland trout streams into this temperature range for extended periods, particularly in late afternoon. Fishing a trout stream on a 38-degree day in February is not catch and release fishing in any meaningful sense. It is catching fish and watching them die slowly downstream.

The ethical response to this is to not fish those conditions. Go early, when overnight cooling has brought temperatures down, and stop when the water warms. Or target a different species whose thermal tolerance is more compatible with the conditions. This requires honesty about priorities — the desire to fish versus the commitment to sustainable practice — and not everyone will make the same choice. But the information is available and the consequences are knowable.

Hooks, Handling, and the Details That Compound

Several smaller factors compound in their effect on post-release survival and are worth addressing briefly.

Barbless hooks, or hooks with the barb crimped flat with pliers, reduce dehooking time significantly. A fish that requires thirty seconds of handling to remove a barbed hook from deep in its jaw has experienced far more stress than a fish from which a barbless hook slips free in three seconds. The argument that barbless hooks lose more fish is partly true and mostly irrelevant — if your goal is sustainable catch and release, the fish's welfare after release should outweigh your interest in landing every fish that bites.

Deep-hooked fish present particular challenges. A fish hooked in the throat or gut suffers from a hook that is difficult to remove without causing significant internal damage. The correct protocol for a deeply-hooked fish that you intend to release is to cut the line as close to the hook as possible and return the fish. The hook will rust out over time in most cases. Attempting to remove a deep hook by force causes far more damage than leaving it in place.

Proper release technique is the final element. A fish should not be thrown back into the water. It should be held gently, right-side up, facing into any available current, and supported until it shows signs of active recovery — the ability to hold itself upright and resist gentle pressure from your hands. Some fish recover in thirty seconds. Others, particularly those that have been fought hard or handled poorly, take several minutes. Wait. Release the fish when it is ready to go, not when you are ready for it to go.

Catch and release is a practice worth doing. It is also a practice worth doing properly, because the alternative — a feel-good ritual that masks ongoing harm to fish populations — serves no one.