Temperature, detection of Perca fluviatilis and Hemimysis anomala winter swarm in Lake Geneva. A) Water temperature (blue line), daily sum tracks of H. anomala recorded by the high-frequency acoustic camera (green triangles) and daily P. fluviatilis detections from infrared video monitoring (orange bars, March 15–30, 2022). Counts for March 15 and 18 (completed) and March 24 and 25 (no direct observations) were predicted from a GAM (95% confidence intervals, CI95). Abundance values of H. anomala for days lacking complete acoustic coverage were similarly predicted with associated CI95. B) Mediation model depicting the direct and indirect effects of water temperature on daily perch detection, and H. anomala swarm abundance. Path coefficients were estimated from linear regressions; the indirect effect (a × b) was computed by bootstrap (10,000 iterations). Solid arrows indicate significant effects (p < 0.05), dashed arrows non-significant effects (p > 0.05). Arrow colour denotes the direction of effect (blue = positive, red = negative).