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Spawning Characteristics of Adfluvial Rainbow Trout in a North Idaho Stream: Implications for Error in Redd Counts
Author(s) -
Holecek Dean E.,
Walters Jody P.
Publication year - 2007
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/m06-049.1
Subject(s) - rainbow trout , tributary , environmental science , range (aeronautics) , fishery , hydrology (agriculture) , zoology , trout , population , fish <actinopterygii> , biology , geography , geology , cartography , geotechnical engineering , sociology , composite material , materials science , demography
Abstract We examined redd microhabitat characteristics of an adfluvial population of rainbow trout Oncorhynchus mykiss in Trail Creek, a third‐order tributary to Deep Creek in the Kootenai River drainage, Idaho. We also monitored timing of spawning in relation to stream temperature and discharge. A total of 103 suspected redds were found; 51 of these were measured and checked for the presence of eggs. Thirty‐four were actual redds (contained eggs), while 17 were test digs that did not contain eggs. Rainbow trout began spawning on 14 April 2005, 13 d after peak discharge (1.9 m 3 /s), as mean daily temperature exceeded 4.0°C. Redds had a mean area of 1.19 m 2 (SD = 0.62; range = 0.27–2.40 m 2 ), a mean water depth at the pit head of 0.18 m (SD = 0.08; range = 0.05–0.38 m), and a mean water velocity at the pit head of 0.39 m/s (SD = 0.15; range = 0.08–0.67 m/s). Area, total length, and width were the only microhabitat variables that differed statistically between redds and test digs; the mean area of the test digs was 0.72 m 2 (SD = 0.67; range = 0.22–2.60 m 2 ). However, the ranges of microhabitat measurements for redds and test digs overlapped; therefore, distinguishing redds from test digs based solely on size, without verifying the presence of eggs, is unlikely. These data could be used to help guide spawning habitat enhancement projects or to create or quantify spawning habitat for adfluvial rainbow trout. The presence of an appreciable number of test digs indicates that redd counts should not be considered a surrogate for numbers of spawning adfluvial rainbow trout; additionally, our results have implications for the use of redd counts to monitor other adult salmonid populations.