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Long‐Term Trout Production Dynamics inValley Creek, Minnesota
Author(s) -
Waters Thomas F.
Publication year - 1999
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(1999)128<1151:lttpdi>2.0.co;2
Subject(s) - trout , rainbow trout , brown trout , salvelinus , salmo , fishery , zoology , biology , biomass (ecology) , stocking , ecology , fish <actinopterygii>
Long‐term studies in Valley Creek, Minnesota, continued from April 1965 to April 1986. Initially, the brook trout Salvelinus fontinalis was the only trout species present, but both rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta later entered the study section. Brook trout declined after severe floods, recovered, declined again after an extreme sedimentation, and continued to decline while brown trout increased. Brook trout biomass, initially at 184 kg/ha, decreased to 4 kg/ha at the end of the period, a reduction of 98%. Rainbow trout entered the study section when floods overflowed private ponds, but their population did not reach high levels. After its entrance, the brown trout increased to predominate the trout fauna with a final biomass of 201 kg/ha. At the end of the study period, brook trout biomass remained at 2% of all trout species, rainbow trout at 5%, and brown trout at 93%. Maximum annual production by brook trout, near the beginning of the 21‐year period, was 171 kg/ha. Annual production had declined to only 9 kg/ha (3% of all‐trout production) by the end of the study. Rainbow trout annual production remained low at 8 kg/ha (2%) by the end of the study. Annual production by brown trout increased to 322 kg/ha (95%). Density and mean annual biomass varied similarly over the study period. The ratio of annual production to mean annual biomass (P:B) varied with species, reflecting length of life span: 1.4 for brook trout and rainbow trout, and 1.2 for brown trout. Annual P:B ratios varied among age‐groups, being highest for younger fish. The importance of long‐term studies was emphasized by results of the severe environmental disturbances that ensued during the 21‐year period. The selection of any 1‐ or 2‐year period for study would not have produced an accurate representation of the stream's long‐term biological status.