Inventory of Nearshore Fish Population Densities and Community Structures at Apostle Islands National Lakeshore and Isle Royale National Park

Gorman, Owen; Moore, Seth

Fish communities of the nearshore waters of the Apostle Islands National Lakeshore (APIS) and Isle Royale National Park (ISRO) were studied during the summers of 2003-2004. Objectives of our study were: 1) conduct an inventory of fish species to estimate relative abundances, describe community structures, and identify distribution patterns related to habitat associations; 2) compare nearshore and offshore fish communities in APIS; 3) evaluate the efficacy of various gear to sample fish communities; and 4) provide recommendations for establishing a long-term monitoring and research program. We found the nearshore fish communities of APIS and ISRO to be dominated by a set of common native species, which included lake chub (Couesius plumbeus), ninespine stickleback (Pungitius pungitius), slimy sculpin (Cottus cognatus), burbot (Lota lota), and trout-perch (Percopsis omiscomaycus). The predominant nearshore aquatic habitat of the APIS region was characterized by low slope with sandy substrates while in ISRO was characterized by moderate to steep slopes with coarse and bedrock substrates. Most of the shoreline of APIS and ISRO was exposed to the open lake, but embayments in ISRO provided protected habitat, particularly at the head of bays. Habitat in these protected areas was characterized by low slope, fine substrates and low structure, but harbored relatively diverse fish assemblages with high relative abundances. Species indicative of these protected habitats included spottail shiner (Notropis hudsonius), blacknose dace (Rhinichthys atratulus), and white sucker (Catostomus commersoni). Unprotected areas at the mouth of bays were characterized by high slope, rocky substrates and high structure, but harbored simple assemblages dominated by lake chub. In contrast, nearshore habitat in APIS with high slope and coarse substrates harbored more diverse fish assemblages than areas of low slope and fine substrates. The offshore fish community in APIS was dominated by coregonids and distinct from the nearshore community; only slimy sculpin held a position of strong importance in both communities. At a regional scale, the similarity in composition of nearshore fish communities of APIS and ISRO suggests that the fish communities of the nearshore waters of Lake Superior are drawn from a common source pool and that differences in habitat characteristics and protection from the open lake determine the local composition and structure of those communities. The lake chub was the most distinctive feature of the nearshore fish community as it was both unique to nearshore waters and was an abundant, conspicuous member of that community. Of four gears used to sample nearshore fish communities (seines, bottom trawls, Windermere traps, fyke nets) only Windermere traps sampled fish over the full range of nearshore habitats in both APIS and ISRO. For long-term monitoring of nearshore fish communities of APIS and ISRO we recommend using Windermere traps supplemented by fyke nets and electrofishing at intervals of 1-2 years. Future research in nearshore waters should address the linkage between nearshore fish communities and that of the open lake, particularly in regard to habitat and life history associations of nearshore and offshore species, spawning and nursery areas for open water fishes, and trophic and energetic contributions of nearshore waters to the Lake Superior ecosystem.

Inventory of Nearshore Fish Population Densities and Community Structures at Apostle Islands National Lakeshore and Isle Royale National Park

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