Who's eating who in the depths of Lake Superior?

Dr. Tom Hrabik is an Associate Professor of biology at the University of Minnesota Duluth.  He co-authored a study called "Trophic connections in Lake Superior Part I: the offshore fish community."  WTIP reporter Carah Thomas spoke with Dr. Hrabik about the study, which had some surprising results.

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International Association for Great Lakes Research
September 13, 2011

A small crustacean, Mysis diluviana, is the primary food source for the majority of open-water Lake Superior fishes.

The Lake Superior offshore fish community has not been studied in great detail in the past, as most sampling in the lake has taken place closer to shore due to time or budget constraints. Offshore, in Lake Superior, is defined as areas with water depths greater than 80 m, or 262 ft. Students and scientists from the University of Minnesota Duluth and the United States Geological Survey collected and analyzed 2,643 offshore fish stomachs, and used that information to describe who’s eating who in the offshore fish community. The primary fish species were siscowet lake trout, cisco (formerly known as lake herring), kiyi (a deepwater form of cisco), and the bottom-dwelling deepwater sculpin. Results indicated that the small crustacean Mysis diluviana (also known as the opossum shrimp) was the primary food source for the majority of offshore fish species.

"We were also interested to discover that cisco were eating the invasive zooplankton species Bythotrephes in the summer and fall," says Allison Gamble, who recently obtained her doctorate from the University of Minnesota working on this topic.

In Lake Superior, the diet items of the dominant offshore fish species did not appear to be in danger from those types of major ecological shifts occurring in the lower Laurentian Great Lakes. Since 80% of Lake Superior is classified as offshore, increased understanding of the food needs of its fish can help management efforts.

Original Publication Information
Results of this study, "Trophic connections in Lake Superior Part I: the offshore fish community," are reported by Allison Gamble, Tom Hrabik, Dan Yule, and Jason Stockwell in the latest issue (Volume 37, No. 3, pp. 550-560) of the Journal of Great Lakes Research, published by Elsevier, 2011.

Contacts
For more information about the study, contact Allison Gamble, Biology Department, University of Minnesota, Duluth, MN 55812; [email protected], (651) 304-7487.

For information about the Journal of Great Lakes Research, contact Marlene Evans, Editor, National Water Research Institute, Environment Canada, 11 Innovation Boulevard, Saskatoon, SK, S7N 3H5, Canada; [email protected]; (306) 975-5310.

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Since 1967, IAGLR has served as the focal point for compiling and disseminating multidisciplinary knowledge on North America's Laurentian Great Lakes and other large lakes of the world and their watersheds. In part, IAGLR communicates this knowledge through publication of the Journal of Great Lakes Research, available to members in print and electronic form. A searchable archive of the journal is available online and includes the abstracts of articles from the journal's inception in 1975 through the most recent issue. In addition, complete articles are available to members who have signed up for an electronic subscription.

Mysis diluviana photo from Wikipedia)