They also are a food source for young perch. The implications for salmon and trout are huge not only to anglers but to people who rely on the money they spend. Various organizations have estimated that sport fishing is worth hundreds of millions of dollars in Michigan's economy annually with money spent on boats, motors, trailers, fishing equipment, gas and lodging. So far, some of the most dramatic effects of the Diporeia decline in the food chain have been on whitefish. Diporeia, once found in concentrations up to 20,000 animals in a square meter of lake bottom, are the favorite food of the whitefish, said Olsen.
Mussels are far less nourishing.
Lake Michigan commercial fishermen aren't the first to see problems with whitefish linked to a Diporeia decline. Randy Owens of the U.S. Geological Survey in Oswego, N.Y., has documented a Diporeia decline of about 90 percent and a corresponding change in the habits and health of whitefish in parts of Lake Ontario. The numbers of whitefish are down, the fish are approximately 25 percent skinnier. Nalepa said the most obvious explanation for Diporeia ' s demise is that the plentiful zebras are feeding first. What is not known, however, is precisely how the zebra mussel is eliminating Diporeia.