Adfluvial and fluvial life history variations and migratory patterns of a relict charr, Salvelinus confluentus, stock in west‐central Idaho, USA

Abstract

– Life history strategies and migratory patterns of 71 adult radio‐tagged bull trout, Salvelinus confluentus, were studied in the Secesh River watershed within the South Fork Salmon River (SFSR) sub‐basin in west‐central Idaho, USA during 2003 and 2004. In both years, upstream migrations occurred during late June and early July, migrations into two spawning tributaries during late July and early August, spawning from mid‐August through mid‐September, and rapid downstream (postspawning) migrations from late August to mid‐September. Primary over‐wintering areas were Loon Lake, the lower Secesh River (downstream of Loon Creek), and the lower SFSR (downstream of the confluence with the Secesh River). Loon Lake evidently provides sufficient production to allow the adfluvial life history strategy to persist and predominate in the Secesh River, while the fluvial life history strategy was previously found to predominate in the nearby East Fork SFSR. Adfluvial, nonconsecutive‐year migrations were the predominant life history strategy. Only seven fish made consecutive‐year migrations to Lake Creek; however, only one of these fish, a female, utilised a spawning tributary in both years and showed spawning tributary fidelity. Three consecutive‐year migrants and three in‐season migrants showed over‐wintering site fidelity by returning to Loon Lake in September, 2004. The life history variations observed for bull trout in the Secesh River watershed are similar to those observed for bull trout throughout their range and to those of other charr species worldwide, yet the development of distinct migration patterns demonstrate the adaptability of the species to a range of available habitats.

Seasonal Movement and Distribution of Fluvial Adult Bull Trout in Selected Watersheds in the Mid-Columbia River and Snake River Basins

“…Prespawning migration start date analysis was hampered by relatively small sample sizes in this study. Most fish in this study spawned in September and had begun postspawning migrations by the end of September, which is similar to previous studies of fluvial bull trout populations in Idaho and Montana [9], [21], [25], [27], [43]. We found that start dates for spawning and postspawning migration in the Imnaha and Lostine rivers, where spawning areas were found at elevations between 1200 and 1600 m in the Wallowa Mountains, were significantly earlier than in Mill Creek, where spawning occurred around 800 m elevation in the Blue Mountains.…”

Relationships between water temperatures and upstream migration, cold water refuge use, and spawning of adult bull trout from the Lostine River, Oregon, USA

“…Tagged fish spawned in 2001-2002 at temperatures 4-5°C higher than previously reported spawning temperatures for bull trout (£9°C) (Pratt 1992;McCullough et al 2001;Watry & Scarnecchia 2008), which is also the criterion in state and federal water quality standards (OAR, 340-041-0028 and 340-041-0151;USEPA 2003). However, we did not expect that adults would also spawn at relatively high temperatures.…”

Modelling individual variability in growth of bull trout in the Walla Walla River Basin using a hierarchical von Bertalanffy growth model

“…It is important not only to appropriately estimate expected values for demographic parameters, but also to quantify variability among individuals (Lloyd‐Jones, Wang, & Nash, ; Marco‐Rius, Caballero, Morán, & Garcia de Leaniz, ; Pilling, Kirkwood, & Walker, ), as individual variability can impact assessment of population dynamics and viability (Peacor, Bence, & Pfister, ; Pfister & Stevens, ; Vindenes, Engen, & Saether, ). Understanding and quantifying individual variability in somatic growth may be especially important for a species such as bull trout ( Salvelinus confluentus ) that exhibits life history variation and for which population viability modelling is needed to guide conservation efforts (Rieman & McIntyre, ; Watry & Scarnecchia, ).…”