Spawning redd habitat use and selection by invasive brown trout ( Salmo
trutta ) along a longitudinal gradient in a headwater stream
Abstract
As stream habitats change from upstream to downstream, choice of
spawning redd sites by brown trout may shift as habitat availability
changes. In a previous study, we examined the importance of overhead
cover in redd site selection. Here, we examined spawning site habitat
use and selection by brown trout by assessing physical characteristics
at redd sites in a 4.8-km reach of Garvin Brook during each of five
spawning seasons, 2016–2020. We measured redd dimensions, water depths,
and current velocities, and compared these among four separate sections
(900–1900 m in length) of the stream. We also assessed available
habitats within each section to examine possible selection of habitats
by spawning trout, plus quantified the size distribution of gravel
substrate at redd sites within two stream sections. Habitat availability
varied dramatically among stream sections. After analyzing 1844 redds
from the five spawning seasons, brown trout displayed strong selection
for water depths between 10 and 29 cm and current velocities between 10
and 49 cm/sec when choosing redd locations. Preferred/selected water
depths and current velocities increased by 7 cm and 10 cm/sec,
respectively, between upstream and downstream sections. All redds were
placed in gravel/cobble substrates, with variations in size
distributions of gravels not correlated to redd dimensions or any
measured habitat variable. Spawning site preferences of brown trout can
change along a stream reach of moderate length, likely in relation to
changing availability of various combinations of water depth, velocity,
substrate, available cover, and trout abundance.