Proposed Biological Management ofMysis relictain Colorado Lakes and Reservoirs

Abstract

The opossum shrimp Mysis relicta has been introduced into many lakes and reservoirs outside its native range to supplement the prey bases for fish. Colorado has received more introductions of the mysid than any other state or province in western North America, but not all of these introductions have been beneficial or innocuous. Mysid predation on zooplankton, particularly cladocerans, has resulted in diminished food for some fishes, especially for planktivores such as the kokanee Oncorhynchus nerka and small trout Oncorhynchus spp. Few fishes forage on the often abundant populations of introduced mysids. Management options are limited in lakes where M. relicta competes for, or has eliminated, the large zooplankters eaten by fish. Furthermore, the mysid has shown enough vagility to expand its nonnative range and may harm fisheries in waters that it enters. Because its eradication is not now feasible, the development of strategies to control or benefit from established mysid populations is warranted. Biological controls appear most feasible. Amphipods and fishes that have the potential to control or benefit from nuisance mysids through competition or predation are candidates for introduction. Of the 13 species that we examined, the deepwater sculpin Myoxocephalus thompsoni was our first choice for introduction into waters containing established mysids. We based this choice on its potential to either control mysid numbers or channel mysid production to predators with little or no adverse effects on the rest of the community.