Thermal refuges: the last line of defense for Atlantic salmon

Heat protocols are often discussed in salmon rivers, but few people truly understand their role and importance in the current context. Yet, the principle is relatively simple. As water temperatures rise, the amount of available oxygen decreases while the salmon's needs increase. The fish must therefore expend more energy simply to maintain their vital functions. Under these conditions, any additional effort becomes more difficult to sustain.

This is where sport fishing comes in, even when practiced exclusively with catch and release. A caught salmon must exert significant effort during the fight. It accumulates physiological stress, produces lactic acid, and draws on its energy reserves. In cold, well-oxygenated water, most fish recover relatively well when handled properly. But when the water reaches high temperatures, this recovery becomes much more difficult. A salmon may appear to be in good condition after being released, but suffer significant consequences several hours or even several days later.

In a context where Atlantic salmon populations were abundant, some might have considered this mortality negligible. Today, the situation is completely different. Several Quebec rivers are experiencing historically low runs and are struggling to meet their conservation goals. Some rivers see fewer than 100 adult salmon return. Others have fewer than 50. At this stage, each spawning fish that manages to reach the spawning grounds represents a significant contribution to the survival of the population.

It is also important to understand that during periods of severe low water levels and high temperatures, fishing is not the only factor that can impact salmon. As water temperatures rise, salmon often congregate in thermal refuges—areas where an underground spring, tributary, or small stream provides cooler water. These areas then become crucial to their survival. In these refuges, salmon are extremely vulnerable. They often position themselves very precisely to take advantage of the narrow corridor of fresh water available. When a swimmer crosses the area, a canoe passes directly into the refuge, or people repeatedly move through the water, the fish can be displaced from their optimal position. Each movement requires additional energy expenditure at a time when they are trying to conserve every available calorie to survive the warmer months. This is why many modern heat protocols don't focus solely on fishing. They also aim to raise public awareness about the importance of respecting thermal refuges and limiting activities that could disturb salmon in these critical areas. When a fish is already struggling with a lack of oxygen, high temperatures, and sometimes several weeks without food, even the slightest disturbance can have far greater consequences than one might imagine.

Of course, sport fishing alone is not responsible for the decline of Atlantic salmon. The problems are much broader and include changes occurring at sea, climate change, habitat degradation, predation, and several other factors that are still poorly understood. However, the fact that sport fishing is not the primary cause does not mean that it has no impact.

particularly in rivers where upstream migrations have become extremely weak.

When the rate of salmon returning to rivers is as low as it is today, every fish that survives to spawn becomes immensely valuable. In this context, the goal of a heat protocol is not to prevent people from pursuing their passion, but rather to temporarily protect the last remaining spawners when environmental conditions reduce their chances of survival. It is a precautionary measure that acknowledges a simple reality: we cannot control what happens at sea, but we can ensure that the salmon that have managed to return to our rivers have the best possible chance of completing their life cycle.

Ultimately, the question isn't whether we enjoy salmon fishing. Most of us are here precisely because we do. The real question is what we're willing to do to ensure its presence in our rivers for future generations. Because when some populations dwindle to just a few dozen fish, conservation can no longer be considered an option. It must become the absolute priority.

A heat protocol is life insurance for the last breeding stock!