Preventing the spread of invasive ruffe. - FWS graphic

Adult Zebra Mussels. - FWS photo

The Ashland National Fish and Wildlife Conservation Office completed a fall investigation of invasive ruffe and other aquatic invasive species (AIS) in four southwestern Lake Superior tributaries.  Bottom trawl sampling verified declines in all ruffe populations, and also detected the presence of zebra mussels in one of the tributary estuaries.  These ongoing investigations were initiated in 1995 to compare trends in relative abundance of ruffe and native fish populations, one of eight elements in the Ruffe Control Plan.  Monitoring is also conducted during spring and summer, and the abundance results are averaged to account for seasonal variation.

Totals of 379 fish representing 18 species and 16 crayfish representing 1 species were captured from all four tributaries, including invasive ruffe.  This compares to a total catch of 6,571 fish representing 21 species captured during this cycle in 2006.  The significant decline (94%) in the total fish catch was likely due in part to low water levels in all tributaries and high turbidity in one tributary.  The total catch included 7 (<2%) ruffe and 11 (<3%) yellow perch.  This compares to total catches of 49 (0.7%) ruffe and 42 (0.6%) yellow perch captured in fall, 2006. 

Yellow perch is a species demonstrated by experimental research to be impacted by ruffe.  Common shiner, johnny darter, and trout-perch were the 3 most abundant species captured, comprising 39%, 16%, and 14% of the total catch respectively.  A total of two zebra mussels were captured from one tributary, the Amnicon River estuary, Wisconsin, a new location for this invasive.  The Amnicon River estuary is located 8 miles east of the Duluth/Superior Harbor, Minnesota/Wisconsin, the only location in Lake Superior known to have a reproducing population of zebra mussels.  No other AIS were captured.

Volunteer assistants included Don Livingston, Red Cliff Tribal Fisheries, on the Iron and Flag Rivers, Wisconsin; Bob Price, independent auto body specialist, on the Amnicon River, Wisconsin; and Jenna Scheub, intermittent with the National Park Service, on the Ontonagon River, Michigan.