Systematic assessment of the increasing presence of white sharks in Atlantic Canadian waters

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Conflicts of Interest

Identified Weaknesses

Rating Explanation

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Paper Summary

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More Jaws in Canada? White Sharks Increasingly Present in Atlantic Canadian Waters

Acoustic monitoring data reveals a significant increase in white shark presence in Atlantic Canadian waters between 2014 and 2023, with a more pronounced trend starting around 2019-2021. Both the probability of migration from US waters and the length of stay within Canadian waters increased substantially. The study acknowledges limitations related to sample size, potential tagging location bias, and changes in tagging methodology but presents a compelling case for a noteworthy shift in white shark distribution.

Possible Conflicts of Interest

None identified.

Identified Weaknesses

Small sample size, particularly in early years

The sample size of tagged sharks was small, especially in the earlier years of the study (2014-2018). This makes it difficult to determine whether the observed increase is part of a larger trend or if there were other factors that could not be accounted for due to insufficient data.

Potential tagging location bias

The study relies on sharks tagged near Cape Cod, which might not accurately represent the movements of all white sharks in the Northwest Atlantic. Some sharks may bypass this area entirely, leading to potential bias in the results.

Potential bias from changes in tagging methodology

The study acknowledges a shift in tagging focus from larger individuals to a more diverse sample of sizes between 2018 and 2019. If there are size or sex-based differences in migration patterns that were not constant over time, the study may not accurately disentangle true trends from a size-related bias.

Uncertainty about the underlying drivers of the observed trend

Although several potential drivers are discussed (prey abundance and climate change), the study cannot conclusively determine the primary cause of the increased white shark presence. Further research is needed to understand the complex interactions at play.

Rating Explanation

This study presents a robust analysis of long-term acoustic monitoring data to show a clear increase in white shark presence in Atlantic Canada. The methodologies are sound, and the authors acknowledge study limitations. While the exact causes remain uncertain and the trend's magnitude has some uncertainty due to low sample sizes in the early years, the overall findings are compelling and contribute significantly to our understanding of white shark distribution shifts.

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