Why were coho and chinook salmon introduced into the Great Lakes?

Coho and chinook salmon were introduced into the Great Lakes for two primary reasons: to establish a new sport fishery and to control the population of alewife.1

Following the collapse of native lake trout populations due to the invasive sea lamprey, the alewife—which had migrated into the upper lakes—multiplied rapidly without sufficient natural predators. These alewives became a nuisance, periodically dying in massive numbers and washing up on beaches, which necessitated costly sanitary operations. By the 1970s, the introduction of these salmon species successfully brought the alewife population into balance. Additionally, the introduction of chinook salmon was particularly successful in Lake Michigan, where it helped revitalize the region's recreational fishing industry.123