Supplementary Material

Table S1. Sampling effort for visible-infrared camera observations of perch detections (number of individuals, n) in March 2022. For each sampling date, observation time slots and total daily duration (hours) are indicated. All times are given in local time (CET).

Table S2. Summary of perch sampling campaigns in Lake Geneva. For each campaign, the sampling type (scientific survey or professional fishers), mesh size of gillnets, depth range, number of analyzed perch and mean total length ± standard deviation (sd).

Table S3. Summary of linear model (LMs) used to estimate the direct and indirect path coefficients (a, b, c) in the mediation analysis between water temperature, perch detections and Hemimysis anomala winter swarm abundance in Lake Geneva. Estimates (β), standard errors (SE), t-values, adjusted R2, and p-values are reported.

Figure S1. Main prey taxa detected in perch (Perca fluviatilis) stomachs using three metabarcoding markers, including MiFish-U (fish-specific 12S rRNA), COI_MG2 (targeting arthropods and other metazoans) and Leray-XT (broad-spectrum COI for invertebrates). Bars show the total number of reads per taxon, partitioned by marker. Only relevant prey taxa were retained (non-prey taxa such as parasites, environmental contaminants or bacteria were excluded). No reads were assigned to Hemimysis anomala.

Figure S2. Droplet digital PCR (ddPCR) quantification of DNA from perch (Perca fluviatilis) and Hemimysis anomala. Left panel: stomach content samples analysed by molecular methods (CARA_1-CARA_16). Right panel: positive controls (H. anomala dilution series at 1000, 200, 8 and 1.6 pg; perch; perch and H. anomala) and negative controls (extraction control, T_ext; no-template control, NTC).

Supplementary Movies S1-S3. Underwater infrared recordings documenting predation of perch (Perca fluviatilis) on Hemimysis anomala in Lake Geneva. These sequences illustrate direct predation events observed during late winter. Available at: https://figshare.com/s/cc03cf128e9ea7c1fb28

Movie S1. Predation event recorded on 18 March 2022 at 04:29.

Movie S2. Predation event recorded on 18 March 2022 at 04:30.

Movie S3. Predation event recorded on 22 March 2022 at 05:58.

Appendix S1. Detailed molecular protocols for perch stomach content analysis.

© H. Rogissart et al., Published by EDP Sciences, 2026