Upper Midwest Environmental Sciences Center
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Mitchell, C. P. (1986). Effects of introduced grass carp on populations of two species of small native fishes in a small lake. New Zealand Journal of Marine and Freshwater Research. 20:219-230.
Stocking Ctenopharyngodon idella (grass carp) for aquatic weed control into a 1.92 ha lake (Parkinsons Lake, 37 degree 19'S, 174 degree 41'E) altered the size and abundance of two species of small native fish, Retropinna retropinna (smelt) and Gobiomorphus cotidianus (bully). The response of the two species differed. R. retropinna recruitment apparently failed during the "high impact" phase of C. idella stocking (44 fish ha super(-1)), when all aquatic weeds were removed. Immature fish disappeared and samples comprised 100% large females. G. cotidianus also increased in size, however, condition improved and the sex ratio did not alter markedly. Following reduction in C. idella stocking density, some return of population meristics toward prestocking values occurred. Loss of the weed bed habitat, water quality deterioration, and increased predation were considered the major environmental impact factors during the period when these changes occurred.
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://www.umesc.usgs.gov/data_library/fisheries/fish_passage/mitchell.html
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