The Importance of Juvenile Migration Tactics to Adult Recruitment in Stream‐Type Chinook Salmon Populations

Abstract

The existence of multiple migration tactics within a population has been observed for several fish species, and they may contribute differentially to adult recruitment. Relative contribution by juveniles using the same habitats on different schedules is variable; therefore, understanding and conserving this diversity should be important to fisheries managers. We investigated adult recruitment by two distinct juvenile migration tactics in several spawning populations of stream‐type Chinook Salmon Oncorhynchus tshawytscha in Idaho: those leaving the spawning grounds as subyearlings during June through November (downstream rearing, or DSR, type) and those emigrating from natal areas 1 year after emergence (natal reach rearing, or NRR, type). The DSR type had greater juvenile abundance in all populations, although the NRR type exhibited better survival from the natal reach to the migratory corridor. The DSR type had greater survival from smoltification to adult return to freshwater compared with the NRR type. More DSR emigrants than NRR emigrants returned to freshwater as adults, although the difference was influenced by cohort and population. Adult recruits to stream‐type Chinook Salmon populations in Idaho are comprised mostly of DSR emigrants, i.e., fish that dispersed from their natal habitats and reared in reaches downstream. This finding is ubiquitous, although the size of the effect depends on cohort and population. We demonstrated that juvenile Chinook Salmon in Idaho do indeed use downstream rearing habitats effectively, thereby increasing recruitment of adults back to the spawning gravels in these populations. This study illustrates how dispersive life histories are essential to achieve the full productive potential of migratory stream fish populations. Received March 31, 2014; accepted July 16, 2014

Setting spatial conservation priorities despite incomplete data for characterizing metapopulations

“…For instance, Copeland et al. () found that a substantial proportion of juvenile spring/summer Chinook salmon in the Snake River rear downstream from their natal streams. Given that imprinting is believed to occur throughout their stream occupancy, this behavior could influence homing accuracy (Westley et al.…”

“…Monitoring dispersal from the natal population to the population in which animals reproduce may not completely represent dispersal processes for species with complex life history strategies such as salmon. For instance, Copeland et al (2014) found that a substantial proportion of juvenile spring/summer Chinook salmon in the Snake River rear downstream from their natal streams. Given that imprinting is believed to occur throughout their stream occupancy, this behavior could influence homing accuracy (Westley et al 2013).…”

Assessing spatial covariance among time series of abundance

“…There could be several mechanisms responsible for this lone latent variable association, one of which could be alternative juvenile life history rearing strategies. Each year some proportion of juveniles leave their natal streams early and rear in downstream habitats in response to habitat and environmental conditions and perhaps other factors, and the Secesh River population is among those with a high proportion of downstream-rearing juveniles (Copeland et al 2014). These types of divergent latent variable association patterns may represent important components to MPG, ESU, and species diversity which may have implications for setting conservation priorities: specifically, prioritizing which populations to target for recovery efforts (A. Fullerton, S. Anzalone, D. Van Doornik, T. Copeland, P. Moran, and R. Zabel, In Review.).…”

Estimating thermal exposure of adult summer steelhead and fall Chinook salmon migrating in a warm impounded river

“…; Copeland et al. ) plus sockeye and coho salmon ( O. kisutch ) with PIT detection histories in recent years. Ideally, empirical exposure data would be collected for these groups to assure that the relationship between observed and predicted DDs is consistent across species and life‐history types.…”

“…Similar population-specific analyses could be conducted for the dozens of wild and hatchery populations that are PIT-tagged in the Snake River basin each year (e.g., Muir et al 2001;Garcia et al 2004). There are also many stream-type Chinook salmon (e.g., Achord et al 2007;Copeland et al 2014) plus sockeye and coho salmon (O. kisutch) with PIT detection histories in recent years. Ideally, empirical exposure data would be collected for these groups to assure that the relationship between observed and predicted DDs is consistent across species and life-history types.…”