An Evaluation of Rearing Densities to Improve Growth and Survival of Hatchery Spring Chinook Salmon

Abstract

We evaluated growth and survival of spring Chinook salmon Oncorhynchus tshawytscha reared at varying densities at Warm Springs National Fish Hatchery, Oregon. For three consecutive brood years, density treatments consisted of low, medium, and high groups in 57.8-m3 raceways with approximately 16,000, 24,000, and 32,000 fish/raceway, respectively. Fish were volitionally released in both the autumn and spring to mimic the downstream migration timing of the endemic wild spring Chinook salmon stock. Just prior to the autumn release, the rearing density estimate was 4.24 kg/m3 for the low-density group, 6.27 kg/m3 for the medium-density group, and 8.42 kg/m3 for the high-density group. While weight gain did not differ among density treatments (P = 0.72), significant differences were found in median fork length (P < 0.001) for fish reared at different densities. Fish reared at high density exhibited the highest on-hatchery mortality rate during two brood years; however, differences in mortality rate among densities were not significant (P = 0.20). In one brood year, adult recovery rates appeared to support the hypothesis that lower initial densities improved postrelease survival (P < 0.01). All rearing densities utilized in this evaluation were relatively low and may partially explain why more differences were not readily apparent among density groups. In addition, the volitional release was a confounding factor in our study because we were unable to quantify the number of fish released in the autumn.

A Synthesis of Findings from an Integrated Hatchery Program after Three Generations of Spawning in the Natural Environment

“…The rearing densities maintained at the CESRF were generally at the lower end of the range reported by Chinook Salmon rearing studies (Ewing and Ewing 1995). Reduced rearing densities may confer behavioral and survival advantages to hatcheryorigin fish (Brockmark and Johnsson 2010;Olson and Paiya 2013). We also used factorial mating at the CESRF, which can increase effective population size (DuPont-Nivet et al 2006; and thus conserve genetic diversity.…”

Exploring the Biological Basis of Age-Specific Return Variability of Chinook Salmon (Oncorhynchus tshawytscha) From the Robertson Creek Hatchery, British Columbia Using Biological or Physical Oceanographic Explanatory Variables

“…Banks and LaMotte [39] found that rearing density had a minor, inconsistent effect on smolt to adult survival. Olsen and Paiya [40] reported mixed effects of lower density on adult survival; however they thought their low, medium and high experimental densities would all be considered to be low rearing densities. They, and [41], suggested that lower rearing densities enhanced survival when ocean conditions were poor.…”

Effects of Hatchery Rearing Density, Handling, and Nutrition on Renibacterium salmoninarum Infection Prevalence in Juvenile Chinook Salmon

“…The weight and length were recorded for five individuals from each chamber before inoculation to determine experimental biomass. The densities for each tank were consistent with Soderberg et al (2013) and Olson and Paiya (2013). Density was treated as a whole plot treatment.…”