WORK ELEMENT B: Increase steelhead smoltification rate and decrease residuals at WNFH.

In FY22, a four broodyear experiment of split-age rearing was completed, and smolts from this release year will complete their migration at the end of the performance period.  Split-age rearing allocates steelhead fry to age-1 or age-2 smolt release groups according to their growth potential with fast-growing fish smolting at age 1 and slow-growing at age 2. Fixed-age rearing groups (no sorting for growth potential) released at age-2 or age-1 were the control groups. We hypothesize that (1) split-age rearing produces higher smoltification rates and lower male maturation rates than fixed-age rearing, and (2) Split-age rearing results in higher survival and faster migration speed than the fixed-age rearing. PIT tagged steelhead from both methods were measured and assessed prior to release, and their migration survival rate and speed will be estimated using PIT tag detection data during their migration throug through the Columbia River.  The split-age treatments (ages 1 and 2) will be combined by broodyear (BY) for comparison to the fixed-age controls of the same BY.

FY 2023 TASKS

Task 1: Mark-recapture models will be developed that account for smolt age, migration year, broodyear, and body size, and used to compare survival rates for the two rearing methods over the four BYs.

Task 2: Migration speed will be analyzed using General Linear Models for the two rearing methods over the four BYs.  

Task 3: The complete 4 broodyear pre-release data set will be analyzed to estimate and compare smoltification rates, residualism rates, male maturation rates, and volitional release efficacy rates between hatchery steelhead reared using the split-age and fixed-age rearing methods.

WORK ELEMENT C: Identify physiological traits affecting growth and their genetic basis to minimize domestication selection.

Energy available for growth is determined by metabolic processes. In fishes, metabolic rate can vary threefold among individuals after controlling for other factors and show temporal stability for individuals in consistent environments, such as hatcheries. Metabolism in fish is measured indirectly as oxygen uptake rates using respirometry.  The standard metabolic rate (SMR) is the minimum energy required to sustain homeostasis, and excess energy is used for growth and activity.

FY 2023 TASKS

Task 1: In the FY22 performance period repeated measurements of oxygen uptake for 84 steelhead were obtained at four points during hatchery rearing and prior to seawater challenge assays.  In the FY23 performance period this data will be used to estimate individual SMRs from the oxygen uptake data, determine variability among individuals, and temporal stability within individuals to determine if metabolic phenotypes exist in hatchery steelhead. Strength and direction of correlations between SMR, growth and smoltification will indicate how metabolic phenotypes influence growth and smoltification traits and their role in domestication.

Task 2: In the FY22 performance period, a pilot study revealed significant variability for individual embryos using static respirometry, indicating embryos are more metabolically diverse than previously thought. We will investigate the developmental timing of metabolic phenotypes by improving respirometry techniques for embryos and alevins using intermittent flow respirometry to better estimate SMR at these critical life stages.  Knowing the developmental timeline for metabolic phenotypes affecting growth traits will determine when to implement hatchery rearing interventions to increase their effectiveness.  

Task 3: Development of swimming respirometry capacity to measure additional aspects of metabolic phenotypes (maximum metabolic rate, and aerobic scope), and to assess how hatchery rearing affects swimming performance.  Aerobic scope estimates the energy available for activities (migration, feeding, predator avoidance, growth) that directly impact post release survival.

Task 4: Investigate the genetic basis of growth and seawater survival traits using 1,200 genetic samples collected during a FY21 laboratory experiment.  Genetic data (RADseq and and whole genome) will be analyzed to determine the role of family effects on smoltification, identify regions of the genome under selection in hatcheries, and estimate breeding values for growth and seawater challenge mortality using genomic prediction.