Some Factors Affecting a Hatchery-Sustained Kokanee Population in a Fluctuating Colorado Reservoir

Abstract

Abstract The population of kokanees Oncorhynchus nerka in Lake Granby, Colorado, is expected to satisfy the competing demands of providing summer harvest for anglers, kokanee eggs for restocking. and prey for trophy lake trout Salvelinus namaycush In the late 1970s. declines in numbers of kokanees harvested and kokanee eggs collected prompted investigations of the influences of stocking rates, reservoir fluctuations, competition with Mysis relicta, and lake trout predation. The kokanee population has been maintained mainly by annual stocking of fry (≤30 mm total length. TL) since 1951. When maturing spawners exceeded 367 mm TL, more than 50% of them were harvested in the summer recreational fishery. which reduced the number of kokanees in some fall spawning runs. However. when maturing year-classes were composed mainly of smaller kokanees. proportionately fewer were harvested. and the number of maturing kokanees entering the spawning run increased. Despite a trend of increased stocking from 1951 to 1978. ...