Matching trawl dates within seven days retained a northward mean catch-center shift for 21 fish species at 194 eastern Bering Sea stations, 1982–1991 to 2015–2025

We tested whether survey-date matching changed a mean northward fish catch-center shift. We used public NOAA trawl data for 21 early-selected fish species at 194 eastern Bering Sea stations. We compared 1982–1991 with ten surveys in 2015–2025; 2020 had no survey. One-to-one matching within seven days kept every station and 1,681 pairs. Mean biomass catch centers moved 20.67 km north after matching and 20.22 km with all dates. The paired difference was +0.45 km, with an approximate 95% three-survey block resampling envelope of −4.03 to +3.90 km. Three-day matching also kept all stations and gave 19.52 km north. The primary date gap fell from 6.59 to 3.69 days earlier in the late period. Matching retained the mean northward pattern but did not resolve a change in the mean. Individual species estimates changed by up to 16.11 km. Matching also changes year weights and leaves residual date differences. It does not isolate seasonal movement or a climate cause. The package preserves raw data, source hashes, pairs, code, all resampling draws, figures, and independent calculation checks.

species distribution · bottom trawl · Bering Sea · survey timing · date matching · biomass catch center · reproducibility