Effects of Freshwater and Marine Growth Rates on Early Maturity in Male Coho and Chinook Salmon

Abstract

In many populations of salmonid fishes, a fraction of the males mature at a younger age than the females; these males are termed jacks if they have migrated to sea and precocious parr if they matured in freshwater. We examined detailed data on the University of Washington hatchery populations of coho salmon Oncorhynchus kisutch and Chinook salmon O. tshawytscha for more than 30 years to test whether rapid growth in freshwater or at sea increases the probability of early maturity in males. The average size of Chinook salmon smolts (2.6–20.9 g) increased over the years in question. The proportion of males maturing as jacks increased with smolt size but not with the potential for growth at sea. The size of the smolts (but not growth potential at sea) was positively correlated with the proportion of the jacks maturing after only one summer at sea (so‐called minijacks) rather than two summers. In coho salmon, average smolt size (6.1–22.4 g) did not vary consistently with time. There was a slight tendency for cohorts with larger smolts to produce more jacks, but marine growth potential was negatively related to the proportion of jacks. For neither species did marine environmental variables influence the proportion of jacks. Taken together, these results support the hypothesis that size prior to seawater entry has the predominate effect on the probability of early maturation and that the growth potential at sea has a neutral or even inhibitory effect on early maturity.

Accuracy of nonmolecular identification of growth‐hormone‐transgenic coho salmon after simulated escape

“…The smallest of these fish was 61.3 g and 189 mm, which is larger than the size at which most normal coho salmon undergo the smolting process (average of typically ,25 g) found at this time of year (Vo¨llestad et al 2004). The largest of the transgenic fish was 238 g and measured 278 mm.…”

Life history effects on hatchery contributions to ocean harvest and natural-area spawning

“…Additionally, fall run Chinook salmon held for extended rearing peri-ods and released the following fall, as "yearlings" tend to mature later than earlier releases (Hankin 1990). Among wild salmon, however, size at ocean entry is negatively correlated with age at maturity (e.g., Vøllestad et al 2004), and so yearling releases (of larger fish) may not delay maturity in all cases, although timing effects may predominate over the effects of size at release.…”

"Research to Improve the Efficacy of Captive Broodstock Programs and Advance Hatchery Reform Throughout the Columbia River Basin." [from the Abstract], 2008-2009 Progress Report.

“…Evidence for strong heritability in age-at-maturity comes from quantitative genetic studies (Hankin et al 1993;Heath et al 1994;Heat et al 2002) and measures at the population level (Hard et al 1985, Appleby et al 2003. Physiological traits mediated by environmental conditions (e.g., body size, fatness), can trigger early male maturation (Vøllestad et al 2004;Shearer et al 2008). Early male maturation may represent the default developmental pathway, with the slower growing males repressing maturation until the following year (Aubin-Horth 2005).…”

“…In this study the effects of two environmental factors, photoperiod (at emergence) and food availability (growth during early rearing), on seasonal timing of smolting, smolt quality, and age of male maturity are being examined in spring Chinook salmon. We chose to examine these factors because previous studies have shown that emergence timing ( Beckman et al 2007) and growth during critical periods of the life cycle affects the proportion of males maturing at early ages relative to females (Rowe and Thorpe 1990a,b;Rowe et al 1991;Silverstein et al 1998;Shearer and Swanson 2000;Campbell et al 2003;Swanson et al , 2005Vøllestad et al, 2004;Shearer et al 2006). …”