Trawl catches reveal differences in prey fish community from north to south in Lake Winnipeg
Ann Arbor, MI — Estimates of prey fish biomass depend on when and where you sample in Lake Winnipeg. Greatest biomass of the non-native prey fish rainbow smelt was found in the deeper, cooler waters of the north basin compared to other regions of the lake. In contrast, biomass of native emerald shiner and cisco was greater in the south basin and the channel regions of the lake, compared to the north basin. Juvenile walleye biomass was greatest in the south basin, followed by the channel, and the north basin.
To better understand patterns of the offshore fish community across time and space, researchers from Manitoba Water Stewardship Fisheries Branch, and Fisheries and Oceans Canada conducted midwater trawls throughout Lake Winnipeg during spring, summer, and fall from 2002 to 2008. Sampling cruises were made possible by the Lake Winnipeg Research Consortium. Trawl surveys were conducted with funding from DFO Species at Risk and other Canadian Government funds and from the Fisheries Enhancement Fund.
Greatest total prey fish biomass was found in the shallow (mean depth = 9.7 meters), more turbid south basin of the lake compared to the channel or the north basin. Of the six most commonly caught species in midwater trawls, biomass of five species was greatest in the south basin during the summer or the fall compared to the spring.
Prey fish are an important part of aquatic ecosystems, acting as a key energy link between lower levels in food webs and top predators that consume prey fish, so it is important to understand how factors associated with sampling affect biomass estimates of prey fish. As no lakewide trawl studies have been reported for Lake Winnipeg, results from this study form a baseline against which ecosystem changes, such as nutrient levels in the lake or establishment of non-native species, can be assessed.
Original Publication Information
Results of this study, "Temporal and spatial patterns in pelagic trawl fish catches in Lake Winnipeg," are reported by Chelsey Lumb, William Franzin and Doug Watkinson in the special issue on Lake Winnipeg, of the Journal of Great Lakes Research, published by Elsevier, 2011.
Contacts
For more information about the study, contact Chelsey Lumb, Manitoba Water Stewardship, Fisheries Branch, 200 Saulteaux Crescent, Winnipeg, MB, R3J 3W3, Canada; chelsey.lumb@gov.mb.ca, (204) 945-7796.
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; jglr@ec.gc.ca; (306) 975-5310.
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