The fish communities of nearshore and offshore waters of Lake Superior: Patterns, trends and connections

The fish community of the nearshore zone of Lake Superior has been the focus of investigations and monitoring for over 50 years.  The nearshore zone (< 81 m depth and <5 km offshore) contains a fish community dominated by lake cisco, bloater, lake whitefish, rainbow smelt, and lean lake trout.  The offshore zone (> 80 m depth and >5 km offshore) has received far less attention; comprehensive surveys were begun in 2001 provided a picture of relatively simple and potentially stable fish community dominated by siscowet lake trout, kiyi, and deepwater sculpin.  Examination of species distributions across depths ranging from 20 to > 300 m revealed three species assemblages.  The aforementioned nearshore and offshore fish communities occurred in the <81 m depth zone and at depths >160 m, respectively.  The intermediate 81-160 m depth zone contained a mix of species from nearshore and offshore zones.  Size and age of some species increased with depth so that juvenile and adult life stages occupied different depth zones.  Other species showed concurrent distributions of juveniles and adults.  Diel, seasonal and ontogenetic movements of fish across habitats appear to facilitate connectivity and energy transfers between shallow and deep water zones.