The science of steelhead

Note: Recently an angler responded to a post on the Wild Steelheaders Facebook page, arguing that instead of managing some rivers solely for wild steelhead we should use "brood stock wild fish" to create "superior hatchery fish," interbreeding would become "mute" [sic], and that this mixture of hatchery and wild steelhead would create "healthy stocks with ample supply for spawning and retention [harvest]." This angler also demanded the post's author, John McMillan, publish his research that documented small male resident rainbow trout successfully spawning with adult female steelhead -- a significant nexus between resident and anadromous forms in the life histories of O. mykiss.

One of the highest priority goals of the Wild Steelhead Initiative and Wild Steelheaders United is to share the most current, rigorous science on steelhead biology and management with the angling community, to better inform the people who care the most about steelhead. The kind of response required here is too detailed for a Facebook comment, so we have posted John's response here and encourage readers to share it widely.

By John McMillan

First, the identification and implementation of Wild Steelhead Gene Banks [as currently proposed for several Puget Sound rivers in Washington] is not something that I or Trout Unlimited proposed. Rather, it is a key component of WDFW's Wild Steelhead Management Plan. The concept is something that was worked on for a number of years and was subject to public comment and dialogue. 

The science indicates there is a need for both wild and hatchery rivers, so TU supports WDFW's plan. The plan can be found here: http://wdfw.wa.gov/publications/00149/.  There you will find more information on the concept of Gene Banks and their value to recovering wild steelhead populations and supporting wild steelhead fisheries.

And let me be very clear, neither TU nor I personally are trying to get certain rivers designated fly fishing only. We believe it is time to come together as anglers, to support sustainable steelhead runs (wild and hatchery) and to enhance angling opportunities both for catch-and-release and harvest, rather than continue the old culture war. We strongly believe this approach is a win-win for all steelhead anglers.

Second, we are not altogether opposed to wild broodstock hatchery programs for steelhead. However, to claim that hatchery fish derived from wild broodstock are "superior" is misleading.

This 2014 paper by Christie et al (Christie et al. 2014 reproductive success of early gen hatchy fish.pdf) on the survival and fitness of broodstock programs indicates that using local wild fish for hatchery broodstock, even for only one - three generations, produces fish that -- on average -- survived at only 50% the rate of wild fish. 

The lower survival rate means that interbreeding between the hatchery broodstock and wild fish is not "moot." Instead, it means that interbreeding with the local broodstock would reduce survival of the hatchery x wild offspring, resulting in a less productive population. The paper reviewed all relevant case studies where wild broodstock fish were used, so it is as comprehensive as we could hope for at this time. 

Third, there is substantial evidence that small resident rainbow trout males breed with larger female steelhead. In fact, my research on the Quillayute River system was the first published paper to document that type of behavior, and in some years -- particularly late in the season after male steelhead are depleted because of their fighting -- those little resident males maybe the only available mate for female steelhead. 

Additionally, we have genetic data by scientists such as Todd Seamons indicating that in some years up to 50% of the steelhead in Snow Creek (WA) had small resident male fathers. There is also published research indicating that female rainbow trout produce steelhead. This is not surprising. For decades scientists have known that small resident males are a key component in the biology of Atlantic salmon.

I not only provide the published research here, but also this video clip that I took in the Quillayute of a small resident male "sneaking" in to mate with a female steelhead. The "sneak" behavior is something that salmonids have evolved to allow small males to avoid aggression from larger males and as we see, behaviorally and genetically, it works! 

The "sneaking" behavior is now broadly accepted in the scientific community, and as found in McMillan et al. 2007 (McMillan et al. 2007 steelhead.pdf), hatcheries tend to produce small precocious males that may also mate with wild female steelhead. This is something that was not well understood, but is becoming an increasing concern to fishery managers.

Fourth, contrary to the gentleman's assertion, we actually have quite a strong understanding of why some fish smolt and become steelhead while others do not smolt and instead remain in freshwater to become resident rainbow trout. Here is a review paper (Kendall and McMillan et al._2015_Review of anadromy residency in mykiss.pdf) that goes into all of the factors that influence anadromy and residency in rainbow trout and steelhead. The major finding is that fish that become steelhead, or smolts, are more likely to have less efficient metabolisms (faster metabolisms) that require ample amounts of food to grow, and the ocean is one of the only places those fish can find that high level of food.

Further, as you will see in the paper, we have identified several regions in the steelhead genome that are related to smoltification, and they are also related to metabolism and the physiological transition that occurs physiologically in order for the fish to survive salt-water. There are numerous other factors too, and the review paper delves into each of those.

I also include another published paper by myself and others (McMillan et al. 2011[1] influences of condition and environment on early male maturity in mykiss.pdf) explaining how water temperature, growth and fat content are key drivers shaping how and why some males mature as residents at very small sizes.

I am -- first and foremost -- a scientist with an extensive record of peer-reviewed publications. I am also an angler, and an avid one. So I want more angling opportunity, and for future generations to have the same opportunities that I have had. Importantly, I am far from the only scientist to publish on these topics. Read through the additional research [below] to see just how much we do know about steelhead. We believe the best science represents the best foundation for generating new ideas about how to sustainably manage steelhead, and an important component of that sustainability is managing for diversity of steelhead and rainbow trout.

Christie et al. 2011 (Multiple sources of gene flow into a wild population)[1].pdf

Garcia-vazquez et al. precocious parr atlantic salmon.pdf

courter et al 2013 resident rainbow produce anadromous offspring cjfas.pdf

Rundio et al. 2012[1] male biased residency.pdf

 

John McMillan has studied steelhead on Washington's Olympic Peninsula for more than twenty years, and is Science Director for TU's Wild Steelhead Initiative.

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