Length Variation in Age‐0 Westslope Cutthroat Trout at Multiple Spatial Scales

Abstract

Phenotypic diversity provides ecological and evolutionary functions, stabilizing populations in variable environments. Although benefits of larger body size in juvenile fishes are well documented, size variation may have value as well. We explored the distribution of length and length variation in age-0 westslope cutthroat trout Oncorhynchus clarkii lewisi at three spatial scales: area (10 2 km 2 ), stream (10 1 km 2 ), and site (10 0 km 2 ). In addition, we examined relationships between length variables (mean length and interquartile range of length) and instream (temperature and conductivity) and landscape (aspect, elevation, headwater distance, and valley width) variables that were expected to be associated with fish size. Conductivity was included as a surrogate for productivity. Most variation in mean length and interquartile range of fish length was found among areas (62.2% and 62.6%, respectively). Mean length also varied among streams and sites (21.9% and 15.8%, respectively). Similarly, interquartile range of fish length varied among streams and sites (19.1% and 18.3%, respectively). Both length variables were associated with temperature and elevation. Mean fish length was also associated with conductivity, but the association between interquartile length range and conductivity was weak. We conclude that the conservation of variation in phenotypic attributes, such as length, in westslope cutthroat trout may require conservation of viable populations across broad areas and across environmental gradients that are associated with growth.

Sex Ratio, Fecundity, and Models Predicting Length at Sexual Maturity of Redband Trout in Idaho Desert Streams

“…Conductivity (lS/cm) was measured with a handheld digital meter accurate to within 2%. Elevation, a surrogate for temperature (Rieman and McIntyre 1995;McGrath et al 2008), was determined at the lower end of each stream reach sampled using 1:24,000-scale USGS topographic maps and Universal Transverse Mercator coordinates obtained from a handheld Global Positioning System unit.…”

Invasion versus Isolation: Trade‐Offs in Managing Native Salmonids with Barriers to Upstream Movement

“…A reserve‐design algorithm may help optimize this selection on the basis of multiple criteria (Ruckelshaus et al 2003). Managers often lack detailed information for such analyses, so they may seek instead to conserve diverse habitats that support the expression of distinct life histories (Beechie et al 2006; McGrath et al 2009), evolutionary legacies (Allendorf et al 1997), or key production areas for important fisheries.…”

Age, growth and reproductive biology of threatened westslope cutthroat trout Oncorhynchus clarkii lewisi inhabiting small mountain streams

“…Non-hybridized O. c. lewisi populations persist primarily in small, isolated headwater reaches, where they are ostensibly adapted to their local environments and, in common with other salmonids, display large variation in adult life histories that vary within and among populations (Cleator et al, 2009;Downs et al, 1997;Drinan et al, 2012;Fraley & Shepard, 2005;Mayhood, 2000;Rasmussen et al, 2010;Sloat et al, 2005). Growth rates, age at maturity or fecundity are some examples that reflect modification of life-history strategies and have been suggested to reduce extinction risk and contribute to the persistence of O. c. lewisi populations (Carim et al, 2017;Corsi et al, 2013;Kendall & Fox 2002;McGrath et al, 2008).…”