**The title, authors, and abstract for this completion report are provided below. For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**

An Evaluation of the Importance of Mysis relicta to the Lake Superior Fish Community

Edmund J. Isaac², Thomas R. Hrabik², Jason D. Stockwell³, Charles P. Madenjian⁴, and Ora E. Johannsson⁵

² University of Minnesota

1035 Kirby Drive

Duluth, Minnesota 55812, USA

³ U.S. Geological Survey-Great Lakes Science Center

Lake Superior Biological Location

2800 Lakeshore Drive

Ashland, Wisconsin 54806, USA

⁴ U.S. U.S. Geological Survey, Great Lakes Science Center

1451 Green Road

Ann Arbor, Michigan 48105, USA

⁵ Great Lakes Laboratory for Fisheries and Aquatic Sciences

Canada Centre for Inland Waters

867 Lakeshore Rd

Burlington, Ontario L7R4A6, Canada

May 2010

ABSTRACT:

Mysis relicta is a major prey item for many fish species in Lake Superior. However, its importance to an entire fish community as a whole has not been quantified. We described the seasonal prey selection of the major fish species collected across 18 sites in Lake Superior in 2005, and again at five locations in western Lake Superior in 2006 using a selection index (Chesson's α). We also used bioenergetics models to estimate the consumption of prey items by the fish community at the same locations. Additionally, we modeled the production of Mysis, and evaluated this prey resource in terms of demand and supply. We found that rainbow smelt Osmerus mordax, kiyi Coregonus kiyi, and bloater Coregonus hoyi selected for Mysis over other prey items during all seasons, which is consistent with noted diel vertical migrations made by these species and Mysis. Cisco Coregonus artedi selected for calanoid copepods in the spring, and switched to Bythotrephes longimanus in the summer and fall. Lake whitefish Coregonus clupeaformis selected for Mysis in the spring and summer, while all three sculpin species (Cottidae) exhibited random selection for prey. Burbot Lota lota and siscowet Salvelinus namaycush siscowet selected for deepwater sculpin Myoxocephalus thompsoni and Mysis during all seasons, with juveniles showing a stronger selection for Mysis than adults. Mysis was the most consumed prey item lakewide, with higher annual consumption offshore. Predation on Mysis was mainly from rainbow smelt, bloater, and lake whitefish nearshore, and deepwater sculpin and kiyi offshore. Our estimates of Mysis production (supply) were higher than the our estimates of consumptive demand by the fish community at nearly all locations, with this balance suggestive of stability in the food web. A large excess of Mysis production at depths of 80-100 m, where shortjaw cisco Coregonus zenithicus once occupied a population maximum, suggests that shortjaw cisco are not currently food limited. Mysis was found to be a prey item selected for by many fish species, and is directly responsible in supporting nearshore and offshore fish communities. Thus, Mysis plays an integral role in the Lake Superior food web, and is deserving of continued research.