Atlantic Salmon Facing the Challenges of the 21st Century: What Future for Québec?
Text by Hugo Gallier, PhD student in Water Sciences at INRS-ETE (Quebec City, Quebec)
Aquatic ecosystems are increasingly affected by various pressures that shape the diversity of organisms living in these environments. In freshwater, the consequences of climate change and human activities in particular influence fish communities. These pressures alter environmental conditions, which in turn disrupt the life cycle of fish. Migratory species, due to their complex lifestyles and strong ecological adaptations, are even more vulnerable to changes in their ecosystems. Among these migratory organisms, the Atlantic salmon (Salmo salar) faces pressures not only in freshwater but also in the marine environment. For more than 40 years, these cumulative pressures have led to a global population decline as well as drastic decreases in the abundance of Atlantic salmon in Quebec rivers in recent years. Atlantic salmon is a culturally important species for First Nations and for Quebecers. The species is also economically essential for recreational fishing, generating several million dollars per year (House of Commons, 2017). A decline in the abundance of this emblematic species will impact freshwater ecosystems and recreational fishing in Quebec.
Photo credit – Gabriel Guité LeBlanc
Populations in Decline
Atlantic salmon has an extensive distribution range, from rivers in Spain to those in Labrador, Canada. Despite this intercontinental presence, populations of this species have experienced major declines over the past 40 years. These trends can be observed in various ways, such as fishing tonnage or the return rate of spawning adults, and they show an overall decrease in abundance worldwide. As a result of these declines, commercial fishing for wild Atlantic salmon was banned in Canada in 2000. Quebec was the first to implement such restrictive measures in 1972, followed by Nova Scotia, New Brunswick, and Prince Edward Island in 1984.
These restrictions were adopted in Newfoundland in 1992 and six years later in Labrador. Despite these fishing regulations, the return of spawning adults, especially large salmon that spend several winters at sea and therefore have higher fecundity, has continued to decrease. In Quebec, the number of returning large salmon was estimated at 103,500 individuals in 1970, but dropped to 29,700 in 2023 (ICES, 2024). These trends can be observed throughout eastern Canada (Fig. 2), except in the northern part of the country, particularly in Labrador, where total returns of spawning adults have increased from 59,100 individuals in 1970 to 451,200 in 2023 (ICES, 2024). One hypothesis for this northward shift in salmon returns is that environmental conditions in southern rivers, such as rising water temperatures and habitat loss, have become less suitable for the species. Despite these northern increases, the global status of the species remains concerning, and in 2022 ICES reclassified it as “near threatened.”
Fig. 1. Number of returning Atlantic salmon spawners in North America by different
geographic regions from 1970 to 2023
When Climate Disrupts Fish Distribution
The consequences of climate change in marine environments mainly include rising water temperatures, sea-level rise, and ocean acidification. In freshwater, the major effects of climate change are especially visible during summer, with rising water temperatures and decreasing river flows. These environmental variations heavily influence the Atlantic salmon’s life cycle. For example, downstream migration (smolt migration to sea) and upstream migration (spawning return) are influenced by changes in flow rates, while water temperature dictates spawning periods and habitat availability. The cumulative effects of these environmental changes have led to declines in Atlantic salmon abundance in most salmon rivers. According to climate projections from the IPCC (2020), which predict similarly unfavorable or even more severe climatic conditions by the end of the century, Atlantic salmon populations could decline sharply, potentially leading to local extinctions.
Altered Landscapes, Affected Fish
Growing human populations drive constant expansion of urban and agricultural areas as well as forestry zones. Land-use activities modify these environments and can also impact aquatic ecosystems. Beyond reducing and fragmenting habitats, urban areas are major sources of chemical and organic pollution. Agricultural lands also contribute pollutants such as phosphates and pesticides. Additionally, the loss of riparian vegetation leads to the degradation of fish habitats, altering key life processes such as reproduction and predation. Quebec rivers are also home to many dams, including hydroelectric ones. These structures primarily modify hydrological regimes and disrupt—or even block—the connectivity between habitats essential for migratory species like Atlantic salmon, thereby reducing reproductive success. Each of these pressures has a specific impact on Atlantic salmon, but when combined, they can significantly degrade populations.
Fig. 3. Water temperature (a) and current velocity (b) preferences for Atlantic salmon parr (Scruton and Gibson 1993; Stanley and Trial 1995)
Scientific Research to Support the Species
My PhD project (2025–2029) aims to predict the distribution of Atlantic salmon by incorporating climate change and land-use patterns using different modeling methods. I will then study the cumulative effects of these two factors to determine a priority ranking of the most appropriate conservation measures. The study area will initially focus on salmon rivers in Quebec. First, I will examine the influence of land use on Atlantic salmon by analyzing the species' physiological responses to different environmental variables using a bioenergetics model (Fish Bioenergetics 4.0 – Deslauriers et al., 2017). These data, combined with water-quality data and land-use information—urban, agricultural, and forested areas—will allow analysis of each salmon river. Next, I will evaluate population dynamics under increased water temperatures and integrate climate-warming scenarios. Finally, the last objective of my PhD is to study the cumulative effects of land use and climate change to provide expertise supporting protection and conservation efforts for Atlantic salmon using the CEMPRA model (Cumulative Effects Model for Prioritizing Recovery Actions).
Fig. 5. Example (non-representative) of a potential output from the CEMPRA model showing habitat quality for Atlantic salmon according to environmental variables at the mouth of the Sainte-Marguerite River
A Project to Support Protection and Conservation of the Species
The results of this project will help improve our understanding of the cumulative effects of land use and climate change on Atlantic salmon. This project will serve as a decision-support tool to guide conservation and restoration efforts toward the rivers most affected by land-use impacts and climate pressures, both today and in future scenarios. For example, in areas where habitat availability is low and water temperature is high for Atlantic salmon, restoring riparian vegetation could improve both the quality and quantity of available habitat.
Photo credit – Aglaé Lambert / Fig. 6. Atlantic salmon parr caught in the Jacques-Cartier River
