Redd characteristics and implications for survival of Chinook salmon (Oncorhynchus tshawytscha) embryos in the Waitaki River, New Zealand

Abstract

Abstract Chinook salmon (Oncorhynchus tshawytscha) redd characteristics were measured at three locations in the glacially‐sourced mainstem and two locations in small, primarily rainfed, tributaries of the lower Waitaki River. Mean redd size was 17.5 m2 ; lengths of redds ranged from 2.4 to 10 m and their widths ranged from 1.2 to 9.5 m. Water depth (mean ± SD = 0.37 ± 0.09 m) and water velocity (mean 0.68 ± 0.27 m s−1 ) were significantly different between two of the mainstem locations but this may have resulted from differences in site conditions rather than preference by salmon. Substrate permeability, water flow rate through the substrate (termed apparent velocity herein) and oxygen were high in all redds and any “stress” to early fish life stages would likely result from excessive permeabilities (> 55.0 m h−1 ) and apparent velocities (> 0.15 m h−1 ) rather than inadequate water circulation in the substrate. Although salmon did not use all available spawning habitat, in situ redd conditions generally favoured good development and high survival rates.