Network of nearshore protected areas provides important benefits to lake whitefish in the Apostle Islands region of Lake Superior

Abstract

Aquatic protected areas are commonly used for fish conservation, restoration, and management and a spectrum of protection levels exist in the Great Lakes. Using fishery-independent survey data over 43 years, we evaluated whether lake whitefish (Coregonus clupeaformis) population dynamics differed among nearshore partially protected areas (PPAs; commercial fishing prohibited or severely limited), offshore no-take refuges, and unprotected areas in the Apostle Islands region of Lake Superior. Lake whitefish biomass and recruitment to the spawning stock increased at faster rates in nearshore PPAs and offshore refuges than unprotected areas during the initial phase after protected areas were established (1980–2000). Recruitment and biomass stabilized in all management areas in the post-rebuild phase (2002–2022), and mortality was lower in the nearshore PPAs. Mean size of adults decreased within protected areas as abundance increased but not in unprotected areas, suggesting a density-dependent growth response and spillover to the fishing grounds, which was reflected in commercial catch rates. However, nearshore PPAs still harbored larger, faster-growing, and earlier-maturing lake whitefish, likely due to underlying habitat differences. Tag recaptures indicated greater minimum distances traveled near an offshore refuge compared to a nearshore PPA, suggesting habitat gradients may influence boundary porosity. PPAs provided protection and benefits for lake whitefish in areas of higher vulnerability where ceasing all fishing was not reasonable. Great Lakes managers should consider implementing networks of protected areas across multiple habitats as tools for conserving spawning biomass, maintaining diverse population demographics, and preserving portfolio effects to enhance recruitment and population stability.