Data in support of: The eHALK: Comparing Spatial and Environmental Schemes of Data Borrowing for Age Assignment

Fish age-length data are fundamental for understanding key fisheries processes, including growth, mortality, recruitment, and year-class strength. Recent advances in hierarchical modeling and large-scale data aggregation have enabled the development of hierarchical age-length keys (HALKs), which allow information to be shared across systems. HALKs can be structured using various attributes; here, we implement an approach in which data are shared among lakes based on environmental similarity. This repository contains fish records used to develop a HALK informed by environmental data. The dataset was derived from a versioned release of the MidFish database. Because the underlying database has undergone minor revisions since its initial distribution, we provide this archived version to ensure transparency, reproducibility, and consistency with prior work. The database was filtered to include only sport fish species that could be linked to relevant environmental data. It includes two subsets: (1) age-length data used to generate the age-length keys, and (2) length-only records to which the keys were applied. Maintaining discrete, citable versions allows users to align analyses with specific data releases while supporting continued development of the broader MidFish resource. The dataset follows open science principles and is designed to support diverse research and management applications. By unifying fisheries data across jurisdictions, it facilitates collaboration and enables investigations of ecological patterns and management-relevant questions at regional scales.