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Disentangling the Relative Roles of Temperature Changes, Density Dependence, and Predation Risk on the Spatial Distribution of Marine Fishes


Projected sea surface temperature change in the Gulf of St. Lawrence by season, showing years 2046-2065 relative to years 1985-2005, as modelled by the regional downscaling system for a particular scenario.

Climate change is likely to affect the way different species are distributed in the marine environment, although other factors—such as density dependence and predation—are also likely to play a role. Understanding the nature and causes of shifts in species distribution is key to sustainably managing living marine resources. A failure to do so may result in misinterpreting shifts as changes in abundance, or lead to misunderstanding the productivity of a particular species. Using the southern Gulf of St. Lawrence as a model, this project aims to understand the relative roles of different factors, including temperature changes, known to influence the distribution of a number of fish species over the past four decades.

Results: Researchers studied the distribution of grey seals using satellite measurements and aerial surveillance and estimated the distribution of the likely predation effect of grey seals on fish populations. Similarly, annual estimates of the distribution of bottom temperatures and of fish species of interest were produced. The estimated distributions were represented in maps and models that were used to explore the relationships between fish distribution changes and the possible factors responsible for these changes.

Preliminary results from this study suggest that changing species distribution over the past four decades is primarily related to the effects of density dependence (i.e., the rate of population growth depends on the size of the existing population) and the risk of predation by grey seals. The distribution contracted or shifted as fish population size decreased and shifted out of areas of increasing grey seal abundance. Both factors had greater impacts on species distributions than did climate-related changes. The results of this study will be presented in a scientific publication.

Program Name

Aquatic Climate Change Adaptation Services Program (ACCASP)


Atlantic: Gulf of St. Lawrence, St. Lawrence Estuary

Principal Investigator(s)

Hugues Benoît
Fisheries and Oceans Canada

Doug Swain
Fisheries and Oceans Canada

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