March 1, 2023

Habitat degradation is oft cited as one of the major threats to aquatic biodiversity but there are rarely opportunities to quantify this impact across multiple species at broad spatial scales. The Pacific Salmon Foundation has compiled a unique, province-wide dataset of freshwater habitat pressure indicators and salmon population data, visualized in the Pacific Salmon Explorer. Drawing on this resource, our team partnered with scientists at DFO to test the relationships between trends in spawner abundance for 3,689 salmon populations – including all five species of Pacific salmon – and ten habitat pressure indicators quantified for their spawning watersheds.

We found that population-habitat relationships were weak and uncertain at a provincial scale, but certain life-histories and habitat types showed strong responses to some pressures. Although population trends declined with increasing pressure in many of these cases, as expected, in some cases we found positive relationships between pressures and population trends. These apparent positive relationships are unlikely to be due to habitat pressures somehow benefitting salmon, but rather due to confounding factors that benefit both salmon and human development independently (e.g., large productive waterways that are also primary transportation and development corridors). Lead author and SWP Analyst Stephanie Peacock explains why this might be a good thing, “The variable relationships between population trends and habitat pressures at fine spatial scales, and lack of significant trends across species and regions, highlights the diversity and complexity of salmon and freshwater habitats that hinders broad-scale generalizations. But this diversity, if preserved, also offers stability to overall returns in the face of these stressors.”

The Salmon Watersheds Program is currently working on a multi-scale approach to habitat assessment that includes finer-scale information on current environmental conditions, and not just landscape-level pressures, which may clarify the potential for population impacts. As data on habitat pressures, habitat conditions, and population responses accumulate for more watersheds, we will gain a clearer picture of the appropriate spatial scale at which to test population-habitat relationships and target recovery planning.

The paper was published in the journal Ecological Indicators and is available in our Document Library, with all data and code freely available through our Data Library and GitHub repository. Read more about this project here.