F I G U R E 1 in High summer temperatures are associated with poorer performance of underyearling Atlantic salmon (Salmo salar) in upland streams

F I G U R E 1 (a) Locations of sampling sites (circles) in the river Conon catchment, Northern Scotland. The map depicts the area within the black box in the inset map. (b) Daily maximum temperatures recorded in each stream during the study period (points represent the daily highest temperature for the entire stream, so may be either from the upper or lower sampling sites). Red values indicate temperatures>23 C, considered stressful to Atlantic salmon, while yellow values indicate temperatures between 20 C and 23 C, and blue values indicate temperatures <20 C. (c) Density and (d) biomass of underyearling Atlantic salmon, Salmo salar (both on a natural logarithmic scale, ± standard error) in relation to duration of peak temperatures (degree hours above 23 C) at sites in the River Conon catchment (n = 63 sections sampled across six sites in 2 years, 589 fish). All sites had the same initial density and genetic composition of eggs. Temperature: 0–20, 20–23, and>23. Year and sampling position: 2020 Downstream, 2020 Upstream, 2021 Downstream, and 2021 Upstream. Stream: Blackwater, Rannoch, and Vaich.