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Summer Counts of Stream‐Resident Trout Can Differ between Daytime and Night
Author(s) -
Grost Richard T.,
Prendergast Linda
Publication year - 1999
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(1999)019<0837:scosrt>2.0.co;2
Subject(s) - trout , daytime , salvelinus , fontinalis , salmo , rainbow trout , brown trout , fishery , nocturnal , habitat , environmental science , biology , fish <actinopterygii> , ecology , atmospheric sciences , physics
We compared paired daytime and night counts of wild, resident brook trout Salvelinus fontinalis, brown trout Salmo trutta, and rainbow trout Oncorhynchus mykiss made by the same snorkelers within five stream reaches during Aug 1994. Reaches were 66–112 m long and had clear water, flows of 0.14–1.70 m 3 /s, and daytime water temperatures of 9–18°C. Each reach contained four habitat types: cascades, glides, pools, and riffles. Overall, we counted 109 trout in the daytime and 333 trout at night. Counts of trout less than 8 cm long were not different (P > 0.77), but counts of trout 8–15 cm and longer than 15 cm were higher at night than in daytime (P < 0.01 and P < 0.03, respectively). The nocturnal index for trout longer than 8 cm ranged from 58 to 100 among reaches and from 0 to 100 among habitat types. We speculate that trout counted at night were present within study reaches during the daytime but were hidden from view. Biologists should consider that trout behavior and susceptibility to observation may vary substantially between daytime and night, even during summer. In some streams, the majority of trout may not be observable during the daytime.