Mysis Shrimp were introduced into Lake Tahoe to provide a food source for game fish, however they actually reduced the availble food for fish by eating many of Tahoe's native zooplankton. Because their large eyes are sensitive to light, Mysis will migrate 100 feet vertically each day and night in order to escape the sunlight and as a result they are more difficult for the fish to find.

Mysis Shrimp

California and Nevada State Official Agencies introduced one of the most significant species introductions to Lake Tahoe was that of the mysid shrimp (Mysis relicta) which feeds on algae, ditritus, and zooplankton. Mysis were repeatedly introduced into the lake over a three-year period between 1963 and 1965 with the hope that it would supplement the food supply for kokanee and lake trout to produce better sports fishing for the Tahoe angler (Linn and Frantz 1965). Introduction of this organism was successful in a few other lakes (Dodds 2002); however, it was not successful at Lake Tahoe.

The failure of Mysis to supplement food supply for game fish was due to a lack of understanding of (1) the full dietary role of the Mysis shrimp in large and deep oligotrophic lakes, and (2) shrimp behavior, specifically their nightly vertical migration which reduce their utilization by fishes. Mysid shrimp remain near the sediments in daytime and migrate to upper waters at night. In fact, mysids have been shown to migrate enormous distances (400-500 meters) in Lake Tahoe each day (Rybock 1978). Thus, this species has the potential to couple both profundal (dark, deep benthic zones in lakes that do not allow enough light to support photosynthetic organisms) and pelagic (open water) habitats (Chandra 2003).

Mysis introduction was responsible for a dramatic change in the makeup of the Lake Tahoe zooplankton food web (Richards et al. 1975; 1991, Morgan et al. 1978; Threlkeld et al. 1980; Morgan et al. 1982). By the early 1970s, a significant Mysis population had established (> 300/m2). This freshwater shrimp has  been known to prey on other zooplankton; however, due to the limited food sources in Lake Tahoe, this large omnivorous shrimp increased predation on native zooplankton (Rybock 1978) and led to the near-extinction of the zooplankter Daphnia, and important prey species for Kokanee (Cooper and Goldman 1980, 1982). Ironically the introduction of Mysis did not only fail as a food source, it also significantly reduced and important natural prey species. This highlights the need for a science-based component when conducting ecosystem management.