Environmental Correlates of Male Life History Variation among Coho Salmon Populations from Two Oregon Coastal Basins

Abstract

Documenting the spatial scale and possible causes of life history variation among populations of coho salmon Oncorhynchus kisutch can improve ecological understanding and guide efforts to conserve potentially adaptive intraspecific diversity. In this paper I use 14 years of spawning ground survey data for 10 populations from the Coos and Coquille basins on the southern Oregon coast to examine interpopulation differences in the proportion of males that spawn as 2year-old jacks instead of as 3-year-old adults. There were significant between-population differences in the proportions of males spawning as jacks, and mean ''jack proportion'' was significantly and positively correlated with mean spawner density (fish/km). Two principal components (PC1 and PC2) summarizing 98% of the variation in variables approximating stream level environmental conditions explained 60% of the variation in mean jack proportion and 32% of the variation in mean spawner density. Mean jack proportion was negatively and significantly related to PC1, which loaded positively for stream gradient, stream elevation, and smolt and adult migration distance, and to PC2, which loaded positively for distance and negatively for gradient. Mean spawner density was similarly, though not significantly, related to the two principal components. The coefficient of variation for jack proportion was negatively and significantly correlated with mean jack proportion and mean spawner density. Higher-density populations consistently had a higher proportion of spawning males returning as jacks. Because jacks provide the only gene flow between otherwise isolated brood years and may buffer populations from severe brood year loss due to environmental stochasticity, the frequency of this life history strategy critically affects the genetic structure and ecological function in regional coho salmon populations. Explicitly considering the genetic and ecological role of jacks should help improve conservation efforts and future decisions regarding the status of regional coho salmon populations.

Variation in the Probability that Male Coho Salmon Will Mature Early: Inferences from Hierarchical Models

“…Second, similar degrees of intercohort variation in the probability of early maturation have been observed under other sampling and observation schemes. For example, Young (1999) and Vøllestad et al (2004) observed levels of variability similar to those reported here, and much of their data were developed by classifying fish on the basis of length (early-maturing males are short) rather than from tagbased estimates of age. Third, Snover et al (2006) show that changes in the distribution of prey resources at sea may cause the probability of early maturation to span orders of magnitude.…”

“…The strength of regional variation in the probability of early maturation provides new perspectives on results reported by Young (1999). Young (1999) found that interpopulation variation in the probability of early maturation by male coho salmon from 10 streams in 2 basins was best explained by stream-level, rather than basin-level, environmental conditions. Young's (1999) study area was within one of our regions (region 2), and his two basins correspond to our basins 4 and 5.…”

“…Coho salmon from southern populations generally mature at younger ages and have an increased probability of early maturation, whereas the vast majority of fish from Alaska do not mature early Transactions of the American Fisheries Society 137: 70-95, 2008American Fisheries Society 2008DOI: 10.1577 [Article] (Drucker 1972). At smaller scales, even stream-level differences (e.g., the gradients and elevations of streams with a common ocean terminus) among juvenile rearing environments influence the probability of early maturation (Young 1999). In concert with such environmental signals, individual coho salmon that grow fast (Johnsson et al 1997;Vøllestad et al 2004), are large smolts (Hager and Noble 1976), and outmigrate at earlier times (Bilton et al 1982) are more likely to mature early.…”

Application of bioelectrical impedance analysis as a method for estimating composition and metabolic condition of southern bluefin tuna (Thunnus maccoyii) during conventional tagging

“…What is the variation of condition in a school/cohort/population, and does this variation change relative to environment? Do tuna spectrum early into potential breeders and non-breeders, as has been demonstrated for salmon (Young, 1999;Hobday and Boehlert, 2001)? A "condition-survival relationship" could support management and conservation strategies.…”

Spatio‐temporal dynamics of alternative male phenotypes in coho salmon populations in response to ocean environment

“…Demonstrating the dynamics of alternative phenotypes associated with environmental variation, however, has received less empirical attention (but see Young 1999; Healey, Henderson & Burgetz 2000). Using spawning survey data, Young (1999) showed that the proportion of O. kisutch jacks varied within and among streams from two neighbouring river basins, and that the among‐stream variation was related to variation in local demographic (i.e. density) and environmental conditions (stream gradient, elevation and distance to the bay).…”