Mean biomass catch centers moved 4.9 km farther north than number centers for 21 Bering Sea fish species at stations with complete counts, 1982–1991 to 2015–2025

We tested whether biomass and fish-number weights gave different northward catch-center changes on the eastern Bering Sea shelf. We used 21 early-selected fish species and compared 1982–1991 with ten surveys in 2015–2025, without 2020. We matched station support for both measures within each species. This retained 4,042 of 4,074 station-species pairs. Mean biomass centers moved 21.0 km north, and mean number centers moved 16.1 km north. The paired difference was 4.91 km, with an approximate 95% three-survey year-block range of 0.85 to 12.19 km. The mean biomass center lay south of the number center in both periods. The gap fell from 11.63 to 6.72 km. An exact mass-latitude covariance identity accounts for the difference. Scope and omission checks retained its direction. But 32 positive-catch records had missing counts. With all 194 stations kept, at least one fish per missing count, and no upper count limit, sharp closure bounds for the mean difference were −12.73 to +68.77 km. Thus, the signed result applies to complete station support. It does not identify individual movement or a climate cause. The package preserves unchanged source data, provenance, code, results, figures, independent checks, and offline repeat instructions.

fish distribution · Bering Sea · biomass · catch center · missing counts · partial identification · survey data