Comparison of Accelerated Vs. Natural and Freshwater Vs. Saltwater Growth Regimes in the Grande Ronde Basin Spring Chinook Salmon Captive Broodstock Program

The Grande Ronde Basin Spring Chinook Salmon Captive Broodstock Program is designed to rapidly increase numbers of adults spawning in nature.  We collect wild parr and rear them in captivity until maturity, at which time they are spawned.   Their offspring are reared to smolt and released into their parents’ natal stream to complete their life cycle in nature.  Since these fish are maintained in captivity for up to 4 years, many factors contribute to getting the best growth, survival, fecundity and fertility rates.  We tested two different pre-smolt and two different post-smolt rearing regimes to determine which gave us the best outcome.  From the time of capture as wild parr until smoltification, fish were raised under either a simulated “natural” or “accelerated” growth regime.  The natural group was reared with a temperature profile that simulated overwinter rearing, while the accelerated group had a constant temperature year round. From smolt to maturity, these fish were raised either in freshwater at Bonneville Fish Hatchery, or in saltwater at Manchester Research Station.  We compared four production parameters - growth, survival, fecundity and fertility - in order to evaluate the production potential of these different rearing strategies.  We found that accelerated pre-smolt rearing produced larger smolts, however, this difference disappeared by age 3.  Fish raised in saltwater had smaller body size at maturity and the females had lower fecundity and fertility.  Females from the natural pre-smolt rearing group had better survival to maturity and a higher percentage of females maturing at age 5 than the accelerated group, regardless of post-smolt treatment.  The freshwater natural group had the lowest percent of males maturing at age 2 and the highest percentage of males maturing at age 4.  Males in accelerated groups had a higher percentage maturing at age 2 and a lower percentage maturing at ages 3 and 4 than the natural groups.  In a captive broodstock setting, where growth and fecundity are major goals, a freshwater natural rearing regime appears to produce the most offspring.