Two of the smartest fish bio guys I know collaborated to create the article below. Dave Thomas and Arlen Thomasen ( author of the best bug book out there “Bugwater“) also were participants/leaders in the McKenzie River Trout study referenced within the article.
What Happens To Native Trout Fisheries When We Remove Competing Hatchery Stock – The McKenzie River Example
By David Thomas and Arlen Thomason
The native “Redside” rainbow trout of the McKenzie River was an established destination fishery well before World War II. Post-war, ODFW began a program of outplanting out-of-basin hatchery origin fish in the river. In 1963, following their construction of several flood control dams on the river, the Army Corps of Engineers (Corps) built a new trout hatchery adjacent to Leaburg Dam (38.8 river miles above the confluence of the McKenzie River with the Willamette River). The rationale for the hatchery was to mitigate for the losses to the Willamette Basin fisheries caused by the dams. Over the years various stocks of rainbow trout were utilized in the hatchery’s outplanting program. Production was largely managed to meet demands from local anglers rather than any established limits regarding the impact of the hatchery stock on the native Redside population.
Though there had been no systematic population count, local anglers reported that they were encountering increasingly diminished numbers of Redsides, possibly due to interbreeding with or competition from hatchery trout. To partially assuage these concerns, the hatchery stock was converted to a mostly sterile (trisomy) strain. This likely answered any concern regarding gene-flow from hatchery rainbows reducing fitness of the wild spawning fish, but did not speak to possible competition between the native and hatchery stocks for resources (food and habitat). As in any situation where data are scarce, there was considerable disagreement among the fishing communities regarding what, if anything, should be done regarding the status of the Leaburg Hatchery trout program.
In 2009, ODFW announced that it would cease outplanting hatchery fish in a 5.1 mile section of the Lower McKenzie River. Seeing an opportunity to finally estimate the impact of hatchery stock, a group of conservation minded anglers, with cooperation from the local ODFW staff, designed a program to measure the effects of the hatchery stock removal on resident fish populations. Financing for study costs came from donations from local clubs and conservation organizations. From 2010 through 2013, 108 trained volunteer anglers floated and fished the study section using a “mark and recapture” model to estimate the numbers and physical distribution of species. The study involved 277 angling trips for 2,558.5 hours on the river.
After two years from the cessation of hatchery fish planting, the density of native Redside trout in the study section had more than doubled; at the end of the fourth year the increase was more than 300%. In parallel, the number of native spawning cutthroat trout also increased, but to a lesser degree. Interestingly, a parallel study by ODFW using electrofishing methodology came to the same result regarding the proportional changes in the fishery.
As a consequence of this study result, ODFW has continued to refrain from planting hatchery trout in this 5.1 mile section of the river, and the native Redside fishery there has recovered. However, the study results have not resulted in removal of all hatchery trout outplants from the rest of the river, although the study results suggest that it would be possible to quickly reestablish a flourishing native fishery throughout the McKenzie absent the hatchery program The points of resistance for such a wholesale change in managing the fishery are multiple. For instance, some members of the local fishing guides organization feel that the loss of catch and kill hatchery fish would lead to fewer fishing customers, and a resulting reduction of their income. Also, ODFW relies on fishing license sales for a good portion of its fishery management operating budget, and the loss of the abundantly available hatchery stock might conceivably result in a reduction of fishing license purchases. Moreover, the hatchery programs are largely paid for by the Corps as part of its Upper Willamette Basin fishery mitigation obligation. Put another way, these hatchery fish are “free fish” to Oregon, so ODFW works very hard to assure that the programs continued. Finally, ODFW’s Fish Division budget and operations are heavily weighted towards the management and production of hatchery fish. For these reasons, questions regarding the advisability of curtailing hatchery programs are often met with considerable pushback.
Study Website: http://www.mckenzietroutstudy.org/
Final Report: http://www.mckenzietroutstudy.org/reports/
For a history and consequences of Hatchery trout see: Anders Halverson’s An Entirely Synthetic Fish. Published by Yale University Press, 2010.