Removing earlier seine catches reduced the recorded fish richness decrease from 2.34 to 0.81 taxa at eight Wisconsin lakes in 2005–2024

We tested how the end of beach seining affects recorded fish richness in eight Wisconsin lakes. We used the fixed North Temperate Lakes LTER table knb-lter-ntl.7.46. The main panel has 120 lake-years in 2005–2019 and 32 in 2021–2024. Mean richness fell from 17.217 to 14.875 named taxa per lake. Removing earlier seine catches reduced this decrease from 2.342 to 0.808 taxa. Earlier seine-only records supplied 1.533 taxa in an exact accounting split, or 65.5% of the full recorded decrease. This is not a causal share of real species loss. With fixed lakes and shared three-year time blocks, the central 95% range for change without seine was −1.763 to +0.154 taxa. The range depended on the gear and resample rule. Electrofishing, fyke and trammel records gave a decrease of 1.231 taxa, with a time range below zero but a crossed lake-and-year range that included zero. No positive electrofishing row occurs in 2021 at any study lake. An added 2022–2024 check gave a decrease of 0.100 taxa without seine. The positive-catch table cannot distinguish absent gear operation from zero catches or missing records. Other effort changes, gear selection and the short later period limit inference. The result supports a survey comparability audit, not a claim of stable fish diversity or a cause of change. The package preserves exact source data, rights, provenance, code, figures, all results and independent checks.

fish richness · survey gear · sampling effort · lake monitoring · reproducibility · Wisconsin