Influence of maternal habitat choice, environment and spatial distribution of juveniles on their propensity for anadromy in a partially anadromous population of rainbow trout (Oncorhynchus mykiss)

Abstract

This study evaluated the importance of the environment and spatial distribution of juvenile fish for the adoption of alternative migratory tactics in a partially anadromous population of rainbow trout (Oncorhynchus mykiss) from the Santa Cruz River. We captured young-of-the-year fish along the river during autumn 2009, 2010 and spring 2010 and determined their maternal origin (anadromous vs. resident) using strontium to calcium ratios in the otolith core. Relative proportion of anadromous offspring, modelled with logistic regression, increased towards headwaters and in areas with deeper channels and larger substrate composition. Body length, modelled with linear multiple regression, varied positively with site depth, water velocity, substrate size and anadromous maternal origin. Based on evidence for limited juvenile movements (<25 km), the spatial extent of this study (240 Rkm) and the identification of large, contrasting reaches along the river, it is likely that the observed spatial distribution of juveniles and their association to sites with coarse substrate composition reflects maternal spawning activity. Results further indicate that anadromous females breed predominantly in middle and upper river sections in areas with coarse substrate. Given that body size in this system has been positively related to propensity for anadromy, we propose that female spawning choice affects their offspring's spatial distribution, providing the adequate physical template for anadromous offspring to reach or maintain larger body sizes and display anadromy themselves. Relevance of this study is also discussed in the context of alterations in response to future dam construction in one of the latest free-flowing rivers sustaining anadromous O. mykiss.

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

“…There appear to be correlations between the prevalence of anadromy and residency and physical features of river drainages, including drainage size (McPhee et al 2014), stream channel complexity (e.g., Pavlov et al 2001a) and depth (Liberoff et al 2014b), and the presence of lakes (e.g., Russell 1974). These habitat features likely influence and are correlated with several other parameters (e.g., food and temperature), so it is difficult to untangle the specific effects of any single factor.…”

Maternal influence on early lipid content in an introduced partially anadromous population of Oncorhynchus mykiss

“…(). Therefore, the higher nutritional status displayed by anadromous progeny in early stages, coupled with the adequate physical environment determined by maternal spawning site selection (Liberoff et al ., ), might play an important role in the adoption of the anadromous tactic in this population.…”

“…Offspring of anadromous mothers are more likely to become anadromous because they grow faster and achieve a larger size than resident offspring (Liberoff et al ., ). In addition, maternal spawning behaviour determines juvenile rearing habitats providing the adequate physical environment for anadromous offspring to achieve larger body sizes and become anadromous (Liberoff et al ., ).…”

“…Since 1998, this population has been monitored and previous studies indicated that the anadromous and resident forms are now genetically indistinguishable at neutral microsatellite loci (Pascual et al ., ) and can give rise to either life‐history patterns (Riva‐Rossi et al ., ). Previous studies in this system suggest that maternal effects are the main mechanism involved in the perpetuation of anadromy across generations (Liberoff et al ., , ). Offspring of anadromous mothers are more likely to become anadromous because they grow faster and achieve a larger size than resident offspring (Liberoff et al ., ).…”

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“…One study at the stream network scale in the John Day River Drainage in Oregon indicated that stream size influences the frequency of anadromy (Mills et al 2012). Increasing residency in O. mykiss with distance upstream has been observed widely (e.g., McMillan et al 2007), but in at least one case, the opposite trend has been observed (Liberoff et al 2015). The influence of distance per se can be difficult to distinguish from other environmental factors.…”