State‐dependent life history models in a changing (and regulated) environment: steelhead in the California Central Valley

Abstract

We use a state dependent life history model to predict the life history strategies of female steelhead trout (Oncorhynchus mykiss) in altered environments. As a case study of a broadly applicable approach, we applied this model to the American and Mokelumne Rivers in central California, where steelhead are listed as threatened. Both rivers have been drastically altered, with highly regulated flows and translocations that may have diluted local adaptation. Nevertheless, evolutionary optimization models could successfully predict the life history displayed by fish on the American River (all anadromous, with young smolts) and on the Mokelumne River (a mix of anadromy and residency). The similar fitness of the two strategies for the Mokelumne suggested that a mixed strategy could be favored in a variable environment. We advance the management utility of this framework by explicitly modeling growth as a function of environmental conditions and using sensitivity analyses to predict likely evolutionary endpoints under changed environments. We conclude that the greatest management concern with respect to preserving anadromy is reduced survival of emigrating smolts, although large changes in freshwater survival or growth rates are potentially also important. We also demonstrate the importance of considering asymptotic size along with maximum growth rate.

Seasonal age distributions and maturity stage in a naturalized rainbow trout (Oncorhynchus mykissWalbaum) population in southern Chile reveal an ad-fluvial life history

“…The selection of specific habitat, such as inlet streams or a lake, by rainbow trout depends on habitat suitability (e.g., growing areas), food abundance, and growth rates (Northcote, 1992;Quinn and Myers, 2004;Satterthwaite et al, 2010). The habitat in the lake may be more suitable than the inlet streams in the spring due to favorable temperatures in the epilimnion (see Table 1).…”

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

“…California; Satterthwaite et al 2009Satterthwaite et al , 2010Satterthwaite et al , 2012 In laboratory experiment, future smolts had consistently greater growth than nonsmolts, but condition factor of smolts shifted from being greater than to less than that of non-smolts as the time of smolt transformation approached.…”

“…This is generally consistent with what has been documented in Atlantic salmon, where faster growth and larger size early in life are often (e.g., Aubin-Horth et al 2005, but not always (e.g., Bacon et al 2005), linked to male residency. On the other hand, Satterthwaite et al (2009Satterthwaite et al ( , 2010 constructed their model only for female O. mykiss, which appear to express freshwater residency at much lower rates than males Rundio et al 2012;Sloat and Reeves 2014). There is also some evidence of different reaction norms between males and females, resulting in varying influences of growth and size (Doctor et al 2014;.…”

“…Satterthwaite et al (2009Satterthwaite et al ( , 2010Satterthwaite et al ( , 2012 used state-dependent models to simulate the effects of growth and other parameters on female life history patterns in three O. mykiss populations in coastal and central California (Table 2). They predicted that the early emerging and fastestgrowing females would smolt at age 1 or age 2 and that only the latest-emerging and slowest-growing females would become residents, which generally matched empirical observations from these populations ).…”

“…Further, resident males mating with anadromous females (McMillan et al 2007) and the contribution of anadromous offspring from residents and vice-versa (Christie et al 2011;Courter et al 2013;Sloat and Reeves 2014) offer important avenues for buffering genetic and demographic stochasticity that are much less available to other Pacific salmonines . Declines in the anadromous component of O. mykiss populations in the United States, Canada, and Russia have motivated an increased interest in exploring the factors shaping anadromy and residency, especially as changing climate conditions and anthropogenic activities alter the fitness of these different forms (Benjamin et al 2013;Satterthwaite et al 2010).…”