Bennet, S., B. Roper, R. Al-Chokhachy, and P. Budy. 2014. Annual Variation of Spawning Cutthroat Trout in a Small Western USA Stream: A Case Study with Implications for the Conservation of Potamodromous Trout Life History Diversity. North American Journal of Fisheries Management 34:1033-1046. USGS FSP:IP-050825.
Abstract
Little is known about the variability in the spatial and temporal distribution of spawning potamodromous trout
despite decades of research directed at salmonid spawning ecology and the increased awareness that conserving
life history diversity should be a focus of management. We monitored a population of fluvial–resident Bonneville
Cutthroat Trout Oncorhynchus clarkii utah in a tributary to the Logan River, Utah, from 2006 to 2012 to gain
insight into the distribution and timing of spawning and what factors may influence these spawning activities. We
monitored Bonneville Cutthroat Trout using redd surveys with multiple observers and georeferenced redd locations.
We documented an extended spawning period that lasted from late April to mid-July. The onset, median, and end
of spawning was best predicted by the mean maximum water temperature during the first 13 weeks of the year
(F = 130. 4, df = 5, R2 = 0.96, P < 0.0001) with spawning beginning and ending earlier in years that had warmer
water temperatures prior to spawning. The distribution of redds was clumped each year and the relative density of
redds was greater in a reach dominated by dams constructed by beavers Castor canadensis. Both dam failure and
construction appeared to be responsible for creating new spawning habitat that was quickly occupied, demonstrating
rapid temporal response to local habitat changes. Bonneville Cutthroat Trout appeared to establish and defend
a redd for up to 2 d, and spawning most often occurred between similar-sized individuals. Spawning surveys for
potamodromous trout are an underutilized tool that could be used to better understand the distribution and timing of
spawning as well as determine the size and trends of the reproducing portion of populations of management concern.
Without efforts to document the diversity of this important aspect of potamodromous trout life history, prioritization
of conservation will be problematic.