The population of fish-killing sea lamprey is going up in Lake Superior and down in Lake Michigan. The Great Lakes Fishery Commission says about 100-thousand of the parasite are currently in Lake Superior, more than twice the targeted number — and the agency isn’t sure why. But it’s still a fraction of Lake Superior’s all-time high of 800-thousand sea lamprey in the 1950s, when treatments began to reduce the numbers. Lamprey attach to fish and feed on their body fluids. It’s estimated one lamprey can kill about 40 pounds of fish a year.