Are changes in winter weather patterns affecting salmon and trout populations in Wales?

A research paper co-authored by WRc Consultant Scientist Vicki Bewes has been investigating how changes in winter weather patterns are impacting on salmon and trout populations in Wales. The paper, which has been published in Freshwater Biology, was written by the Game & Wildlife Conservation Trust and is based on a project that was completed with WRc (an RSK company) last year for Natural Resources Wales.

The abundance of juvenile Atlantic salmon and trout in Wales has declined over the last two decades and a 2016 recruitment crash coincided with extreme winter weather conditions; this led to speculation that unusually warm temperatures and high flows adversely affect salmonid recruitment.

The article abstract explains, “We developed data‐driven statistical models to: (1) describe juvenile salmonid recruitment from density‐dependent and density‐independent factors; and (2) assess whether the density‐independent factors probably contributed to the 2016 salmon recruitment crash. We compiled salmon and trout young‐of‐year juvenile abundances from electrofishing surveys, egg deposition estimates and river flow and air temperature data from 2001–2017 for seven Welsh rivers, broadly representative of rivers around Wales. We used river flow and air temperature data to derive ecologically and behaviourally meaningful density‐independent explanatory variables.

“Our findings provide empirical support for general and predictable effects of temperature and flow during spawning and emergence on salmonid – especially salmon – recruitment in Wales. Furthermore, we suggest that the 2016 salmon recruitment crash was caused – in part – by particularly inclement spawning and emergence conditions, which could be more common under future climate change. Our findings suggest that future salmonid stock assessment models could include the effects of density-independent variables on recruitment to improve their predictive power.”

You can read the paper in full in Freshwater Biology.