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

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.

Life History Migrations of Adult Yellowstone Cutthroat Trout in the Upper Yellowstone River

“…Over the past two decades, studies of salmonid migrations occurring within freshwater environments (potamodromy) have revealed a much greater degree of complexity than previously recognized (Northcote 1997;Bennett et al 2014). Four distinctive life history migration patterns have been defined in an attempt to categorize the wide range of movements observed: (1) fluvial (spawning and seasonal movements occur within a single stream), (2) fluvial-adfluvial (rearing in large river and spawning in smaller tributary), (3) lacustrine-adfluvial (lake rearing and migration to spawn in inlet tributary), and (4) allacustrine (lake rearing and migration to spawn in outlet tributary; Varley and Gresswell 1988;Northcote 1997).…”

Coastal Cutthroat Trout Redd Counts Impacted by Natural Water Supply Variations

“…Beaver ponds also retain water in lower Irely Creek, thereby providing some rearing habitat while reducing spawning habitat until natural breaching occurs (cf. Bennett et al 2014;McMillan et al 2014).…”

“…To maximize visibility, we tried to avoid storm-induced high-turbidity periods, but correction was occasionally needed for reduced redd detection efficiency at higher flows. For consistency, a single observer identified and counted all completed redds of sufficient size that had definite pits and tailspills (Lowry 1971;Thurow and King 1994;Bennett et al 2014). Trout redds typically showed "scalloping"-pit edges where digging reached fine substrata (including small gravel) for egg burial (Keenleyside and Dupuis 1988;Vadas 2006).…”

Dynamic Habitat Disturbance and Ecological Resilience (DyHDER): modeling population responses to habitat condition

“…Although spawning has frequently been observed in the TF and SC sites (e.g., Bennett et al. ), the actual number of individuals observed spawning in these tributaries is small when compared to the abundance of the total metapopulation (Mohn ). This highlights that, despite being a well‐studied system, unknowns remain regarding the spawning locations and behavior of this BCT metapopulation.…”