A survey date screen reduced the biomass minus catch frequency center shift from 7.8 to 0.2 km for 21 Bering Sea fish species

We compared two northward catch center shifts for 21 fish species at 194 fixed eastern Bering Sea stations. We used open NOAA trawl data from 1982–1991 and 2015–2025, with no 2020 survey. Species were selected from early catches. Each species had equal weight. Mean biomass centers shifted 20.2 km north, while centers based on positive catch frequency shifted 12.4 km. Their paired difference was 7.8 km, with an approximate 95% shared-year block range of 1.7 to 16.0 km. A planned screen kept 105 stations where period mean survey dates differed by at most seven days. The difference then fell to 0.2 km, with a range of −11.3 to 8.3 km. A paired check estimated a 7.6 km reduction, with a range of 2.0 to 18.5 km. The screen also changes station locations, so it cannot isolate a survey timing effect. Capping large biomass catches reduced the difference to 4.6 km and left its interval across zero. We retain and bound all resamples with undefined centers. The result shows a measure contrast that depends on the panel and catch weights. It does not estimate true occupancy, range edges or climate causation. The package preserves source data, provenance, code, all main draws, figures and independent calculation checks.

Bering Sea · fish distribution · bottom trawl · biomass · catch frequency · survey timing · reproducibility