Premium
Some Factors Affecting a Hatchery‐Sustained Kokanee Population in a Fluctuating Colorado Reservoir
Author(s) -
Martinez Patrick J.,
Wiltzius William J.
Publication year - 1995
Publication title -
north american journal of fisheries management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.587
H-Index - 72
eISSN - 1548-8675
pISSN - 0275-5947
DOI - 10.1577/1548-8675(1995)015<0220:sfaahs>2.3.co;2
Subject(s) - stocking , trout , fishery , population , biology , daphnia , daphnia pulex , predation , zooplankton , hatchery , ecology , fish <actinopterygii> , demography , sociology
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. mean kokanee spawner length varied inversely with the reservoir's water volume. In years of low reservoir volume. water temperatures were warmer. This facilitated Daphnia population development, which enhanced survival and growth of stocked kokanees. The colder water temperatures of high reservoir volumes were associated with later appearance of Daphnia , reduced kokanee recruitment. and smaller kokanees. Kokanee overstocking in the late 1970s resulted in stunting during the 1980s and shifted the predominant age of spawners from age 3 to age 4. Overpopulation also diminished angler perception of fishery quality and eliminated Daphnia Pulex , the kokanees' primary food supply. The inverse relationship between reservoir volume and mean kokanee size has persisted despite M. relicta predation on Daphnia and lake trout predation on kokanees. which suggests that thermal and productivity Trends in the reservoir will continue to exert a regulatory role in kokanee population dynamics.