During the August-2023 to July 2024 contract cycle, we will trap, sample, and collect the necessary tissue samples from the 2024 brood of returning adult steelhead at the Twisp River weir, and will collect and sample juvenile progeny in the Twisp River.  All sampling data will be entered in local databases, and the genetic material collected will be transferred to the WDFW Molecular Genetics Lab in Olympia WA, for archiving.

In 2022, we released 65 wild adult steelhead and 38 hatchery adult steelhead upstream of the Twisp River weir. Wild adult steelhead returning to the Twisp weir were generally larger, had a higher fat content, arrived at the Twisp weir earlier, and spawned earlier than hatchery steelhead. However, hatchery females returning to the weir had greater fecundity than wild females. Wild and hatchery steelhead were similar in terms of migration speed, spawn timing and distribution throughout the study years. Preliminary genotyping results from all progeny that have been genotyped suggest that hatchery steelhead had a lower relative reproductive success (RRS) rate than wild steelhead across all years and life stages for which parentage assignments were complete. At the age-1 parr stage, female hatchery steelhead from the 2009-2018 broods were about 74% as productive as wild females, and hatchery males were about 57% as productive as wild males.  

Background on project:

We propose to quantitatively evaluate the relative reproductive success of naturally spawning hatchery and natural origin steelhead in the Twisp River, a tributary to the Methow River in the upper Columbia River Basin.  Hatcheries are one of the main tools that have been used to mitigate for salmon losses caused by the construction and operation of the Columbia River hydropower system.  In addition to harvest augmentation, hatcheries have recently been used in attempts to protect stocks from extinction (e.g., captive breeding) and attempts to enhance natural production (supplementation).  Surprisingly, little is known about how much the investment in hatcheries benefits or harms natural production.  We propose to take advantage of recent technological advances in genetics to empirically monitor the reproductive success of hatchery and natural steelhead using a DNA-based pedigree approach.  For this contract period, we will continue to trap and collect DNA and biological data from all steelhead released upstream of the weir, conduct spawning ground surveys and collect DNA samples from progeny (i.e., parr and smolts) of previous brood years.  Specifically, we will (1) directly measure the relative reproductive success of hatchery- and natural-origin steelhead  in a the natural environment, (2) determine the degree to which any differences in reproductive success between hatchery and natural steelhead can be explained by measurable biological characteristics such as run timing, morphology, or behavior, and (3) estimate the relative fitness of hatchery-lineage steelhead after they have experienced an entire generation in the natural environment.