Detailed diet linkages within the offshore (> 80 m bathymetric depth) food web of Lake Superior are currently not well identified. We used analyses of fish stomach contents to create an empirically based food web model of the Lake Superior offshore fish community. Stomachs were collected seasonally (spring, summer, and fall) from nine offshore locations in 2005, using bottom and midwater trawls. In total, 2643 stomachs representing 12 fish species were examined. The predominant fish species collected were deepwater sculpin (Myoxocephalus thompsonii), siscowet (Salvelinus namaycush siscowet), kiyi (Coregonus kiyi), and cisco (Coregonus artedi). Mysis diluviana was the most common prey item, indicating that changes in Mysis abundance could have a profound impact on the entire offshore food web. Mysis was the primary diet item of deepwater sculpin (≥ 53% by mass) and kiyi (≥ 96% by mass) regardless of depth or season. The invasive Bythotrephes was an important diet component of the pelagic cisco in summer and fall. Deepwater sculpin were the primary diet item of siscowet (≥ 52% by mass), with coregonines appearing in the diet of larger (> 400. mm) siscowet. Non-metric multidimensional scaling analysis indicated that there were no statistically significant seasonal or site-specific differences in diets of deepwater sculpin, cisco, or kiyi. Site was the primary structuring factor in siscowet diets. Generally, in Lake Superior, the diet items of the dominant offshore species did not appear to be in danger from those types of major ecological shifts occurring in the lower Laurentian Great Lakes.
Bibliographical noteFunding Information:
Funding for this work was provided by Minnesota Sea Grant (R/F-15), EPA-GLNPO , USGS Lake Superior Biological Station , University of Minnesota Duluth , US EPA (Mid-Continent Ecology Division, Duluth, MN), Ontario Ministry of Natural Resources , and the Department of Fisheries and Oceans Canada . We are deeply grateful to the crew of the USGS R/V Kiyi, and to Lori Evrard, E.J. Isaac, and Suzan Johnson. This work would not have been possible without their generous assistance. This article was improved by reviews from D. Branstrator, B. Vondracek, M. Stapanian, T. Pratt, C. Madenjian, and J. Kitchell. This article is Contribution 1635 of the U.S. Geological Survey Great Lakes Science Center. Reference to trade names does not imply endorsement by the U.S. government.
Copyright 2011 Elsevier B.V., All rights reserved.
- Diet analysis
- Food web
- Lake Superior
- Offshore fish community