Do young steelhead born in the wild from hatchery parents grow differently than ones born from wild parents?
Steelhead (steelhead are rainbow trout that migrate to the ocean like salmon) have been an important fish species to West Coast humans and ecosystems for thousands of years. Unfortunately, steelhead populations have been in decline on the West Coast since the late 1800s. Causes of these declines include overharvest from commercial fishing, fish passage barriers from hydroelectric and irrigation dams, habitat destruction from human development, and more recently . Historically, the number one way to mitigate for these declines was to raise young fish in a protected environment called a hatchery where a few adult fish could be used to create a large number of juvenile fish. These juvenile fish were then released into freshwater streams to migrate to the ocean and return as adults providing harvest for humans as well as their role in the ecosystems. Unfortunately, recent genetic studies have shown that fish raised in the hatchery from adult hatchery fish become genetically different than steelhead raised naturally in the streams. Additionally, these hatchery fish don’t survive as well in the wild relative to fish raised naturally in the streams. This pattern led to concerns about hatchery fish mating with wild fish and hatchery fish giving “bad” genes to the wild fish potentially hurting wild populations.
To address these concerns, one idea was to implement integrated hatchery practices wherein wild steelhead would be used to create the initial group of adults to produce juveniles. Then as juveniles are released and return as adults the returning adult hatchery steelhead would be continually integrated with wild fish through time. This strategy is thought to minimize differences between hatchery and wild fish and therefore improve a hatchery program's chance of success while also reducing risks to natural populations. Despite this integration, steelhead from hatcheries still perform poorly in the natural environment. One reason for this pattern maybe that when hatchery steelhead produce juvenile steelhead in a natural environment they might not growth as well as juvenile produced by wild steelhead.
A recent paper authored by biologists at Abernathy Fish Technology Center (https://doi.org/10.1002/tafs.10366) examined this idea in Abernathy Creek, WA and found that the size of 1 year old juvenile steelhead were similar in size regardless of whether the juvenile’s parents were from the hatchery or the wild. In fact, they found that yearly differences in creek water temperature and flow were much more important. Additionally, they found that juvenile steelhead from each parent type were found in the same areas spread throughout the creek. These results support that idea that freshwater fish growth is not a mechanism leading to poor hatchery fish success and that the reason may lie at another point in the fish’s life. Also, our results are positive for hatcheries that aid in supplementation of small populations or re-introducing steelhead to habitats where they once were. Conversely, our results point to possible competition for food and refuge habitat among juveniles produced by adults from a hatchery environment and from adults born in the natural environment. All of this means that each hatchery must have clear goals and objectives for the purpose of the hatchery. Lastly, in the context of climate change, higher water temperatures and reduced summer flows could negatively affect juvenile steelhead from each type in the nearing decades.