Bioenergetic evaluation of diel vertical migration by bull trout (Salvelinus confluentus) in a thermally stratified reservoir

Abstract

Many species living in deeper lentic ecosystems exhibit daily movements that cycle through the water column, generally referred to as diel vertical migration (DVM). In this study, we applied bioenergetics modelling to evaluate growth as a hypothesis to explain DVM by bull trout (Salvelinus confluentus) in a thermally stratified reservoir (Ross Lake, WA, USA) during the peak of thermal stratification in July and August. Bioenergetics model parameters were derived from observed vertical distributions of temperature, prey and bull trout. Field sampling confirmed that bull trout prey almost exclusively on recently introduced redside shiner (Richardsonius balteatus). Model predictions revealed that deeper (>25 m) DVMs commonly exhibited by bull trout during peak thermal stratification cannot be explained by maximising growth. Survival, another common explanation for DVM, may have influenced bull trout depth use, but observations suggest there may be additional drivers of DVM. We propose these deeper summertime excursions may be partly explained by an alternative hypothesis: the importance of colder water for gametogenesis. In Ross Lake, reliance of bull trout on warm water prey (redside shiner) for consumption and growth poses a potential trade‐off with the need for colder water for gametogenesis.

Physiological condition and migratory experience affect fitness‐related outcomes in adult female sockeye salmon

“…Katinic, Patterson, & Ydenberg, ; Newell & Quinn, ). Yet, our observation that tagged females did not use the coolest temperatures available was consistent with previous studies that have shown fish to select intermediate temperatures in lakes (Armstrong et al., ; Eckmann, Dunham, Connor, & Welch, ). At low temperatures, sockeye salmon have reduced aerobic scope for oxygen‐dependent processes, such as swimming.…”

“…tures in lakes (Armstrong et al, 2016;Eckmann, Dunham, Connor, & Welch, 2016). At low temperatures, sockeye salmon have reduced aerobic scope for oxygen-dependent processes, such as swimming.…”

Thermal heterogeneity, migration, and consequences for spawning potential of female bull trout in a river–reservoir system

“…Previous research has shown that bull trout have strong behavioral and physiological responses to their habitat, including temperature and prey availability (Eckmann et al, 2018; Gutowsky et al, 2017; Selong et al, 2001). Our study complements these by exploring how movement patterns and associated temperatures can influence growth potential across a heterogeneous river–reservoir system.…”

“…Bull trout may shift among thermal heterogeneous locations for various reasons such as predator avoidance, prey availability, or maximum growth (Selong et al, 2001; Gutowsky et al, 2017; but see Howell et al, 2010). Recently hypothesized is that bull trout may occupy colder temperatures to improve gamete viability (Eckmann et al, 2018) or minimize metabolic costs (Armstrong & Bond, 2013). Temperature is an important driver in reproductive development and egg viability in female fish (Jobling, Johnsen, Pettersen, & Henderson, 1995; Rideout et al, 2005).…”

“…Bull trout is native to the eastern Pacific Rim of North America (Dunham et al, 2008), and among the most cold‐adapted of all aquatic vertebrates in the region (Benjamin, Heltzel, Dunham, Heck, & Banish, 2016; Dunham, Rieman, & Chandler, 2003; Isaak, Wenger, & Young, 2017). Patterns of thermal habitat use have been studied directly or indirectly via telemetry within rivers (e.g., Howell, Dunham, & Sankovich, 2010; Paragamian & Walters, 2011; Swanberg, 1997) and lakes and reservoirs (e.g., Eckmann, Dunham, Connor, & Welch, 2018; Gutowsky et al, 2017), but there are no studies of the consequences of thermal habitat use by individuals moving through these linked river–reservoir systems. Our overall goal in this study was to address this gap by conducting an integrated analysis of thermal habitat use by bull trout moving through linked river–reservoir systems.…”