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.
Many of the rivers studied also suffered flooding in the spring of 2016, potentially causing ‘egg washout’ whereby eggs are washed out of the spawning nests, known as redds, into unsuitable habitat where they are likely to die. These washouts are more severe in steep rivers susceptible to flooding, as is common across Wales.
Source: Game & Wildlife Conservation Trust