[1] Univ Minnesota, Minnesota Sea Grant, Duluth, MN 55812 USA
[2] Michigan Sea Grant, E Lansing, MI 48824 USA
[3] US Geol Survey, Biol Resources Div, Great Lakes Sci Ctr, Lake Super Biol Stn, Ashland, WI 54806 USA
[4] Univ Vermont, Sch Nat Resources, Aiken Ctr, Burlington, VT 05405 USA