Abstracts

Assessing the Lake Winnipeg fish community response to a 2XCO² climate scenario

Alex Salki¹Greg McCullough, William Franzin, Walt Lysack, and Brenda Hann
¹Freshwater Institute, Fisheries and Oceans Canada
salkia@dfo-mpo.gc.ca

Lake Winnipeg, the world's10th largest freshwater lake, is well suited to study the influence of regional climate variation on aquatic ecosystems because it spans 3.7º N latitude. June-October monthly mean surface temperatures (MST) were modeled for the period 1909-2000. The only significant trend detected was a 0.14ºC decadal warming rate in the South (S) basin during August which is comparable to low end global predictions by IPCC. Maximum MST occurred in August in both the North (N) (21.9ºC) and the S (24.5ºC) basins. The CGCM-II model (forcing scenarios A2 and B2, Canadian Centre for Climate Modelling and Analysis) predicts increases of 2.2-2.5ºC and 2.9-5.1ºC in July and August Lake Winnipeg MST by 2045 by 2085, respectively.

Our attempt to predict the most probable Lake Winnipeg ecosystem response to 2xCO² for adapting fisheries management included defining thermal tolerances and temperature preferenda of all Lake Winnipeg fish species, evaluating historical commercial and index fishing data, and examining fish food items (forage fish, benthos, zooplankton) collected during lakewide surveys in 2002 and 2003. Weak spawning stock-recruitment correlations indicate that environmental factors (e.g. rate and length of vernal warming, growing degree-days) may be important during pre-recruitment years (age 0 - 3) for walleye, sauger, and whitefish. Lake Winnipeg fish community sustainability may also be influenced by several concurrent factors, known direct fishery effects and indirect effects from eutrophication, lake regulation, food web changes and exotic species introductions. These complexities and the absence of long-term juvenile fish data currently preclude establishment of a definitive fishery management strategy within a 2xCO² climate regime.

2005-04-05