A new study from the Salmon Watersheds Lab has found significant evidence that human activity in estuaries is impacting juvenile Pacific and Atlantic salmon. The team’s review of 167 peer-reviewed studies (from an initial search of 13,000) identified negative impacts from several stressors, including the effects of flood-protecting tidal gates, pollution and habitat modification.

Dr. Emma Hodgson, a post-doc researcher with the Salmon Watersheds Lab (SWL) at the time of the research and lead author on the paper, says the review is the first to synthesize what is known, and not known, about how human activities in estuaries may impact juvenile salmon.

“Risk can be defined by the severity of the impact and the certainty we have about whether that impact is likely—that certainty is based on the amount of evidence and agreement between the evidence,” Dr. Hodgson says.

The review summarized more than 1,300 statistical tests related to the biological impacts from 14 stressors to determine the environmental impacts of human activities.

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One stressor the review identified as likely to have a negative impact on salmon populations, is a reduction in connectivity from the presence of tide gates. These metal gates are designed to reduce flood risks, but can also cut off access for salmon to parts of a river.

For example, in one study reviewed, the number of juvenile salmon found above tide gates was 2.5 times lower than in free-flowing rivers.

The review also identified such stressors as light and noise pollution, which have potentially severe negative impacts on salmon, but which have been poorly studied.

Dr. Jonathan Moore, head of the SWL and co-author on the paper, hopes this review will help guide stakeholders and decision-makers in being effective stewards of juvenile salmon and their estuarine habitats.

“Natural resource managers need to make tough decisions, in short timeframes, about the potential environmental risks of proposed developments and whether they should go ahead,” says Dr. Moore. “They won’t have time to wade through thousands of papers when making these decisions, so we did it for them.”

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Media: SFU News.