Numbers of young salmon in Wales are lower following warmer winters and wetter springs, according to a new study commissioned by Natural Resources Wales (NRW). These findings might explain the widespread juvenile salmon crash observed after the then record warm and wet winter and spring of 2015-16.
While salmon stocks have declined across southern European rivers for some time, a widespread crash in juvenile salmon numbers in 2016 saw a sharpened focus into what drives their numbers and so might have caused the crash. Low juvenile numbers, as seen in 2016, can have a knock-on effect on adult returns in future years.
Concerned about the impact, NRW commissioned WRc plc and the Game & Wildlife Conservation Trust (GWCT) to analyse data collected on seven Welsh rivers (the Clwyd, Conwy, Dee, Teifi, Tywi, Usk and Wye) between 2001 and 2017 with a particular focus on 2016.
Focusing on ‘young-of-the-year’ salmon and trout (those from eggs hatched that spring), the study, due to be published in Freshwater Biology, found that juvenile salmon – and to a lesser extent trout – numbers were lower following warm winters and wet springs and that the 2016 salmon crash coincided with extreme winter and spring weather conditions.
Warm winters can present a real challenge to salmon and trout, with increased temperatures negatively impacting both spawning behaviour and egg survival. The winter of 2015-16 was notable for its exceptionally high temperatures around the time of salmon spawning, leading to speculation that those high temperatures interfered with normal salmon spawning behaviour.