After linear trend removal, trout catches showed no clear extra correlation within 13 English management catchments, 2000–2025

We tested whether trout catch indices had higher correlation within management catchments than between catchments at similar distances. We used open English electric-fishing data from 2000–2025. The source taxon, Salmo trutta, includes brown trout and sea trout. The main panel had 3,842 surveys at 232 sites. We removed a linear time trend at each site and correlated residuals in shared survey years. Distance matching had support in 32 bins within 13 focal management catchments. The supported comparison used 3,051 distinct pairs at 185 sites. Mean correlation was 0.187 within catchments and 0.151 between catchments. The difference was +0.036, with a 95% joint catchment and shared-year resampling interval of -0.104 to +0.178. Survey adjustment, rank correlation, narrower distance bins and other supported checks did not resolve a positive extra correlation. Strict date control had no supported comparison. The initial annual-change design also lacked support; we preserve that plan and the amendment made before the contrast was inspected. The result does not establish equal correlations or independent risk across boundaries. Catch indices are not calibrated fish density, and management areas do not define connected river networks. The package preserves source data, map queries, code, all results, figures and independent numerical checks.

Salmo trutta · river fish · spatial synchrony · management catchments · England · electric fishing · common support · reproducible research