Science Friday: Revisiting the Carmel River Steelhead Mitigation Program
Written by Natalie Stauffer-Olsen, PhD, TU Staff Scientist
Every now and then we publish something that prompts a reaction from the authors of a report we analyze or others in the science world. This happened with our recent post on the Carmel River that focused on some biological and ecological aspects explored in the paper “Size-conditional smolting and the response of Carmel River steelhead to two decades of conservation efforts” by J. Arriaza, D. Boughton, K. Urquhart, and M. Mangel.
In this case, it sounds like we missed some of the nuance in the paper’s interpretation of the data. More specifically, we want to be clear that the paper modeled projected growth and projected adult returns of wild reared vs wild rescued-&-captively reared steelhead.
The work from this paper was based on accepted bioenergetic principles and annual sizes and estimated numbers of wild reared juveniles, as well as the sizes and known numbers of wild rescued-&-reared juveniles released from the rearing facility. Results of the paper suggested that the larger size of the rescued-&-reared fish that were released and their potential proportion of the estimated annual juvenile population — and at some sites the declining sizes and numbers of wild fish —may have led to the rescued-&-reared fish becoming an increasing and sometimes dominant proportion of the annual run.
However, the authors point out there was insufficient data to do more than hypothesize on the potential negative impacts of relocating rescued fish, and no definitive results on this question were obtained in the study.
Models such as that used in Arriaz et al. (2017) are useful to explore likely possibilities of ecological and biological interactions; however, in order to confirm or deny model findings, field data is necessary and currently substantial effort is being made in the Carmel River watershed to further elucidate findings from the Arriaz research. Additionally, many efforts are being made in the watershed to better monitor and make adaptive management changes to how fish are reared, relocated, and monitored to minimize any potential negative consequences to wild-reared fish and to better inform the operation of the rescue and rearing efforts.
More importantly, significant efforts are being made in the watershed to improve habitat and conditions for wild fish. We commend these efforts because, as we discussed in the post, habitat restoration is a crucial component to the recovery of wild O. mykiss populations in the Carmel River and in many other systems. And as regular readers of our Science posts know, Wild Steelheaders United — through Trout Unlimited programs such as the North Coast Coho Project and Western Water and Habitat Program — is doing extensive habitat restoration, dry season streamflow enhancement, and mitigation of fish passage barriers across the native range of Pacific Northwest steelhead.