Diagnosing and mitigating the adverse effects of extreme climate on salmonid spawning

• Main Author: Diamond, Rowena
• Format: Thesis
• Language: English
• Published: 2022
• Subjects: Q Science (General); Usk; Atlantic salmon; Salmo salar
• Online Access: https://orca.cardiff.ac.uk/id/eprint/156403/; https://orca.cardiff.ac.uk/id/eprint/156403/1/PhD%20thesis%20not%20tracked%20updated.pdf; https://orca.cardiff.ac.uk/id/eprint/156403/2/Publication%20form.pdf

“Salmonid reproduction is highly complex and therefore prone to failure when conditions are suboptimal” (Fenkes et al., 2016). During the winter of 2015/2016, exceptional weather conditions occurred across the United Kingdom, particularly in December when Storm Desmond brought 341.4 mm of rainfall to the UK within 24 hours. This event had a significant impact on many rivers, with the highest winter flows on record (CEFAS, 2017). Unusually warm temperatures, from an extended flow of tropical maritime air, coincided with this extensive flooding, and are believed to have elevated water temperatures, with thermal regimes in some rivers extending above 11°C. This event ensued the salmon spawning season, with temperatures >12°C reported to impact on adult reproduction and juvenile survival in Atlantic salmon (Salmo salar) (Taranger and Hansen, 1993; Solomon and Lightfoot, 2008; Pankhurst and King, 2010; Fenkes et al., 2016). Following this extreme climatic incident, salmonid surveys, for both England and Wales, showed that the density of juvenile salmon captured in 2016 had declined to the lowest levels in the time series. Further consideration of age specific data disclosed that declines were apparent in both fry and parr, with fry deteriorations particularly notable. Following on from these reports, this project was designed to diagnose the cause(s) of the observed declines in Atlantic salmon, linking the loss of salmonids to extreme climatic occurrences. Although this design did indeed shape this thesis, the context evolved to encompass the overall implications of climate on Atlantic salmon, exploring specifically the impact of water temperature on salmon within the Wye and Usk catchments of Wales, and identifying if changes in water quality could likewise be influencing salmon recruitment.