Effects of climate change on the life stages of stream‐dwelling brown trout (Salmo trutta Linnaeus, 1758) at the rear edge of their native distribution range

Abstract

AbstractStreamflow and temperature regimes are key components of the physical habitats of instream biological communities. Iberian brown trout (Salmo trutta) populations exist in a climatic border where water scarcity and increasing water temperatures during summer could compromise their viability throughout the 21st century. We predicted climate change‐induced modifications in the thermal and hydraulic habitats of both the intragravel (eggs and larvae) and free‐swimming (fry, juveniles and adults) stages of brown trout in two mountain streams in central Spain. Spatial–temporal simulations of thermal and hydraulic habitats under two climate change emission scenarios—representative concentration pathway (RCP) 4.5 (mild scenario) and RCP 8.5 (pessimistic)—were conducted at 1‐m altitudinal steps using daily air temperature and streamflow predictions. Increased winter temperatures will reduce embryo and larval development time by 12% (RCP 4.5) and 30% (RCP 8.5) in downstream sites by end of the 21st century, but this reduction might be insufficient to compensate for the shortening of the period with temperatures below the viability limits for survival of intragravel phase (20% and 54%, respectively). Combining streamflow and temperature data for free‐swimming stages indicated that the suitable summer habitat will be reduced by between 53% and 76% (RCP 4.5) and 70%–90% (RCP 8.5) by 2099. The predicted effects for all developmental stages are critical for determining population viability at both ends of its altitudinal distribution. However, these responses are river‐specific, as limiting factors differ among rivers.