Montana's 1968 shrimp introduction triggers salmon collapse and harms eagles and bears

In 1968 Montana wildlife managers released opossum shrimp (Mysis diluviana) into lakes such as Whitefish and Ashley, aiming to increase food for sport-fishing kokanee salmon. The shrimp migrated downstream and established a dense population in Flathead Lake by the late 1970s, reaching about 130 individuals per square metre by 1986. Their nocturnal, bottom-dwelling behavior prevented salmon from exploiting them, while the shrimp consumed Daphnia and other zooplankton crucial for young salmon.

The abundant shrimp also supported a boom in lake trout, which began preying on the dwindling salmon. Consequently, the iconic salmon spawning runs in McDonald Creek disappeared by 1989, and the loss cascaded to bald eagles and grizzly and black bears that had depended on the salmon carcasses for winter fat. The altered food web shifted Flathead Lake from a surface-water salmon fishery to a deep-water system dominated by non-native trout, also pressuring native bull trout and westslope cutthroat trout.