Experimental fish were collected by electrofishing (LR-20B; Smith-Root, Vancouver, WA, USA) carried out over a 500 m stretch at each study site (Appendix S1, Table S1) between May 11 and June 11, 2019 (Appendix S1, Table S1). All sampled brown trout were measured (fork length i.e., from the tip of the snout to the end of the central caudal fin ray) and a small clip of the pelvic fin (~0.5 cm2) was stored on ice and later in laboratory kept in freezer at -80 °C, awaiting stable isotope analysis. We have collected between 38 to 45 brown trout per sampling site with average fork length ranging from 93 to 143 mm (Appendix S1). Aquatic macroinvertebrates for fatty acid and bulk stable isotope analysis were collected using kick sampling and terrestrial macroinvertebrates were collected by hand-picking and dragging the kick net over the canopy surrounding the stream. The macroinvertebrate samples were collected at each sampling site the same day as the fish and were stored alive in an icebox and after determination in the laboratory kept frozen at -80 °C until further processing. Habitat quality was evaluated at each study site on July 10, 2019 using standardized protocol (Jönköpingsmodellen - Halldén et al. 2002, Appendix S1, Table S1) and photographs of habitats at each sampling site were taken (Appendix S1, Fig. S1). Consumption of aquatic macroinvertebrates by brown trout is known to increase with their abundance in the stream (Evangelista et al. 2014; Sánchez‐Hernández & Cobo 2018). Therefore, we performed a quantitative assessment of abundance and biomass of aquatic macroinvertebrates at each sampling site on July 11 and 12, 2019 during sunny stable weather, with no precipitation and low water flow. Aquatic macroinvertebrates were collected by a kick-net (30 x 25 cm, mesh size, 30 seconds of kicking at three spots within each study site representing all available habitats). Macroinvertebrates were counted and oven-dried at 60 °C for 48 hours and total dry biomass of macroinvertebrates at each sampling site was measured to the nearest 0.001 g (Appendix S1, Table S1).