Anadromy and residency in steelhead and rainbow trout (Oncorhynchus mykiss): a review of the processes and patterns

Abstract

Abstract:Oncorhynchus mykiss form partially migratory populations with anadromous fish that undergo marine migrations and residents that complete their life cycle in fresh water. Many populations' anadromous components are threatened or endangered, prompting interest in understanding ecological and evolutionary processes underlying anadromy and residency. In this paper, we synthesize information to better understand genetic and environmental influences on O. mykiss life histories, identify critical knowledge gaps, and suggest next steps. Anadromy and residency appear to reflect interactions among genetics, individual condition, and environmental influences. First, an increasing body of literature suggests that anadromous and resident individuals differ in the expression of genes related to growth, smoltification, and metabolism. Second, the literature supports the conditional strategy theory, where individuals adopt a life history pattern based on their conditional status relative to genetic thresholds along with ultimate effects of size and age at maturation and iteroparity. However, except for a generally positive association between residency and high lipid content plus a large attainable size in fresh water, the effects of body size and growth are inconsistent. Thus, individuals can exhibit plasticity in variable environments. Finally, patterns in anadromy and residency among and within populations suggested a wide range of possible environmental influences at different life stages, from freshwater temperature to marine survival. Although we document a number of interesting correlations, direct tests of mechanisms are scarce and little data exist on the extent of residency and anadromy. Consequently, we identified as many data gaps as conclusions, leaving ample room for future research.Résumé : Les truites arc-en-ciel (Oncorhynchus mykiss) forment des populations partiellement migratrices incluant des individus anadromes qui effectuent des migrations marines et des individus résidents dont le cycle biologique se déroule entièrement en eau douce. Les éléments anadromes de nombreuses populations sont menacés ou en voie de disparition, ce qui suscite un intérêt envers la compréhension des processus écologiques et évolutionnaires qui sous-tendent l'anadromie et la résidence. Nous présentons une synthèse de l'information disponible dans le but de mieux comprendre les influences génétiques et environnementales sur les cycles biologiques d'O. mykiss, de cerner les lacunes critiques en matière de connaissances et de proposer des avenues de recherche future. L'anadromie et la résidence semblent témoigner d'interactions entre la génétique, l'état des individus et des influences environnementales. D'abord, de plus en plus d'études donnent à penser que les individus anadromes et résidents diffèrent sur le plan de l'expression des gènes associés à la croissance, à la smoltification et au métabolisme. Deuxièmement, la documentation appuie la théorie de la stratégie conditionnelle selon laquelle les individus adoptent un m...

Declining patterns of Pacific Northwest steelhead trout (Oncorhynchus mykiss) adult abundance and smolt survival in the ocean

“…The phenotypic plasticity of steelhead, including iteroparity and the existence of nonanadromous rainbow trout that are often functionally part of the steelhead population (Courter et al 2013;Kendall et al 2015), and the difficulties associated with accurately counting the fish (e.g., low abundance, protracted arrival timing, and often difficult surveys) can challenge our ability to detect trends in population abundance. For example, declining survival during migration to and from the ocean and in the ocean can lead to an increase in the proportion of resident individuals in O. mykiss populations (Kendall et al 2015).…”

“…For example, declining survival during migration to and from the ocean and in the ocean can lead to an increase in the proportion of resident individuals in O. mykiss populations (Kendall et al 2015). Thus, steelhead population abundance declines may not represent a trend towards that population's extirpation but may instead suggest a change in the dominant life history strategy.…”

“…This is due in part to their complex life history (Behnke 2002;Kendall et al 2015;Pavlov et al 2008;Quinn 2005), which makes estimating basic abundance, productivity, and survival metrics difficult. Specifically, adult steelhead enter fresh water over a protracted time period, whereas adult Pacific salmon do so in a more compressed period (Quinn 2005).…”

Density dependence and its impact on individual growth rates in an age‐structured stream salmonid population

“…The resultant densities as observed in the summer and fall might therefore not reach levels that affect individual growth rates. In an evolutionary perspective, this behavior is a driving factor in the development of anadromy (Gross 1987, Kendall et al 2015.…”

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“…These studies detected three juvenile Rainbow Trout/ steelhead in the mainstem Columbia River (fish that had been initially captured and tagged in Rattlesnake and Buck creeks), indicating an attempt at anadromous migration nearly 100 years after Condit Dam had blocked upstream access. Resident and fluvial Rainbow Trout are known to contribute to anadromous populations (Hayes et al 2012;Weigel et al 2013;Kendall et al 2015) and have been shown to speed population recovery after disturbance (Parker et al 2001). A juvenile fish assessment with a rotary screw trap was conducted by USGS and USFWS for four years, beginning in 2006, to determine species composition and abundance of salmonids in the river downstream of Condit Dam (Allen and Connolly 2011).…”