MidFish: A harmonized freshwater fish survey data resource for fisheries research and management

Abstract

Agencies across North America monitor freshwater fish populations to assess status and trends and to evaluate the effectiveness of management actions. Leveraging monitoring data across regions can improve the statistical power to detect change and evaluate management outcomes, but differences in sampling protocols, database structures, and terminology require integration of disparate data sources to enable effective use. We present MidFish, a publicly available data resource consisting of a harmonized database with reproducible and customizable workflows that integrates fish survey data from seven Midwestern states spanning 1937–2023. MidFish contains over 60 million individual fish records from 133,227 surveys across 8,431 water bodies, including over 21 million records with fish length measurements. Data were harmonized into a database of individual fish with fields containing information on individual fish characteristics, surveys, and lakes. Survey gear, effort, and purpose are included to enable calculation of relative abundances while accounting for differences in sampling methodologies. We provide customizable workflows that allow users to generate data sets or aggregated metrics tailored to specific analyses. Two example applications include generating standardized catch-per-unit-effort data sets for eight sport fish species and estimating time to harvestable size for Walleye Sander vitreus across lakes. MidFish provides a foundation for regional analyses of fish populations, growth, and size structure, and demonstrates how data sharing and harmonization can increase the scientific and management value of long-term fisheries monitoring programs more broadly.