Iteroparity in complex mating systems of steelhead Oncorhynchus mykiss (Walbaum)

Abstract

This study investigated diverse reproductive types in complex mating systems of steelhead Oncorhynchus mykiss. Postspawned steelhead (kelts) were sampled during attempted downstream migration over Lower Granite Dam on the Snake River, U.S.A. Multilocus microsatellite genotypes (14 loci) were used to assign unknown origin, kelt individuals to upstream populations of origin. Results indicated that iteroparity is a life-history trait that remains in several tributaries of the Snake River basin despite strong selection against downstream adult passage because of hydroelectric dams. The largest populations of steelhead in the Snake River, however, were only weakly represented (Clearwater River ¼ 7Á5% and Salmon River ¼ 9Á4%, respectively) in the kelt steelhead mixture relative to the Grande Ronde River (18Á2%), Imnaha River (17Á4%), Pahsimeroi Hatchery (25Á2%) and Asotin Creek (22Á2%). A lack of correlation between population escapement size and kelt proportions (P > 0Á05) suggests that iteroparity was not uniformly expressed across populations, but was significantly negatively correlated with body size (P < 0Á05). Iteroparity may be a valuable source of genetic variability and a conservation priority, especially in years with poor recruitment or in recently bottlenecked populations.

Survival and Traits of Reconditioned Kelt Steelhead Oncorhynchus mykiss in the Yakima River, Washington

“…We did find that reconditioning survival decreases with increasing fish length ( Figure 5), which supports this notion; however, the mean FL of kelts in our collection was 63 cm; few fish in the collection were longer than 78 cm, a size-class more commonly found in the Snake River, and the decrease in survival rate with increasing length was slight. We did find that an increase in spawner density negatively affected the proportion of kelts collected in the Yakima River,which could also explain why the largest populations in Narum et al (2008) had the lowest kelt proportions collected at Lower Granite Dam.…”

Iteroparity in Columbia River summer-run steelhead (Oncorhynchus mykiss): implications for conservation

“…Inferences drawn from the aggregate should not be applied to individual stocks given probable amongpopulation variability in spawner age, sex ratios, initial postspawn survival, and (or) iteroparity. As an example, genetic analyses of kelts collected at Lower Granite Dam showed Snake River populations did not contribute to kelt outmigrations in proportion to population size or distance to spawning grounds (Narum et al 2008). This implies that repeat spawning rates for individual stocks may be much higher or lower than aggregate estimates, particularly for kelts passing lower Columbia River dams, where the mix of Snake, midColumbia, and upper Columbia river fish is most diverse.…”

“…Apparent size-related kelt mortality may therefore also be a function of spawner age. Notably, Clearwater and Salmon river steelhead are relatively abundant among Snake River stocks, but were grossly under-represented in kelt genetic samples at Lower Granite Dam (Narum et al 2008). This suggests initially high postspawn mortality (i.e., on or near spawning grounds) for these large-bodied steelhead, consistent with a more semelparous strategy.…”

Anadromy and the dispersal of an invasive fish species (Oncorhynchus mykiss) in Eastern Quebec, as revealed by otolith microchemistry

“…In our study, three of the 13 fish exhibiting the anadromous life cycle were probably multispawners. Multispawning can increase the success of invaders as this reproductive mode accelerates effective population growth and ensures genetic variability (Riva- Rossi et al 2007;Narum et al 2008a). Multispawning can increase the success of invaders as this reproductive mode accelerates effective population growth and ensures genetic variability (Riva- Rossi et al 2007;Narum et al 2008a).…”