Inland Lake Fish Inventory at Isle Royale National Park

Gallagher, David; Hrabik, Thomas; Glase, Jay; Moore, Seth; Romanski, Mark

The inland lakes of Isle Royale National Park have remained relatively isolated from human impact, providing an opportunity to explore how fish diversity responds to climate change without confounding effects. We analyzed fish assemblages of 23 lakes sampled in the 1920s, 1990s, and 2020s to 1) assess shifts in multiple diversity metrics 2) identify lakes and species experiencing the most change, 3) explore environmental factors driving community structure, and 4) determine changes in length and abundance of common species. We used species-area curves, PERMANOVA, and multivariate dispersion tests to quantify differences in diversity between surveys, temporal beta diversity indices to identify lakes and species changing most, and NMDS to examine lake factors influencing composition. We assessed changes in length and abundance using linear mixed models and Wilcoxon sign-ranked tests. Mean richness and species-area curves did not significantly differ between surveys, although both declined slightly. PERMANOVA and dispersion tests indicated overall community composition and spatial variability remained mostly stable, but larger lakes became more dominated by cool-water species. Species gains and losses were associated with isostatic rebound rate, where lakes with fast and slow rebound rates tended to gain and lose species, respectively compared to prior studies. Overall, these results suggest the inland lake fish communities of Isle Royale have not homogenized over time, but assemblages have gained cool-water and lost several cold-water species. This information will be utilized by park management to revise the 2006 Fisheries Management Plan, preserve and protect genetics of these fish populations, and consider changes to recreational fishing regulations.

Inland Lake Fish Inventory at Isle Royale National Park

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