As part of ongoing efforts to maintain populations of native westslope cutthroat trout, Montana Fish, Wildlife and Parks is proposing to continue removing hybrid and rainbow trout from the Flathead River drainage.
The public has until March 8 to comment on the Flathead River hybrid trout suppression project’s environmental assessment draft, released earlier this month for a 30-day public review. The project could get underway a week later on March 15, according to an anticipated schedule.
In 2001, FWP prepared an environmental assessment for the construction of a fish barrier and manual removal of hybrid trout from Abbot Creek, considered the “primary source of hybridization in the upper Flathead system.” Genetic surveys in 2003 identified four additional tributaries of the main stem and North Fork Flathead River where rainbow trout had hybridized with cutthroats.
An experimental suppression effort was launched in 2005 on the four tributaries: Sekokini, Rabe, Ivy and Third creeks. FWP’s recent proposal is to continue hybrid and rainbow trout removal from the mouths and channels of those four creeks, as well as Abbot.
The environmental assessment draft states that “it is not possible to eliminate hybrid trout from a large, interconnected river drainage such as the Flathead.”
“Nevertheless, results from experimental suppression work suggest that it is possible to reduce the number of rainbow or hybrid trout adults in targeted source populations and help FWP to maintain the current number of identified conservation populations,” the draft states.
A 2007 FWP memorandum of understanding and conservation agreement defined “conservation populations” as trout that contain less than 10 percent hybridization based on genetic data – in other words, at least 90 percent genetically pure westslope cutthroats. Biologists say introduced rainbow trout “readily hybridize” with native westslopes.
The proposal states that trapping and electrofishing would be used to remove hybrid and rainbow trout from the targeted areas during their spring spawning season in April and May. Tributary surveys would then be conducted from July to September. The captured fish would be transported to community fishing ponds.
According to the environmental assessment, FWP is also proposing to remove hybrid and rainbow trout offspring between July and September through electrofishing.
“The goal of the proposed suppression effort is to minimize the loss of westslope cutthroat trout populations considered to be conservation populations, especially the genetically pure portions, in the interconnected Flathead River system,” the draft states.
The suppression efforts, according to the EA, would be repeated annually “until effectiveness can be reassessed,” a period between six and 10 years.
Hybridization’s consequences, biologists say, include the “potential loss of evolved traits in native species that help them thrive in their environment,” “social and economic impacts associated with the decline of unique angling opportunities offered by westslope cutthroat trout” and “the increased potential for listing under the federal Endangered Species Act, affecting management of the species.”
Suppression efforts thus far, according to the EA, have “produced some encouraging initial results,” including a consistent decline in the number of hybrid and rainbow trout captured at target areas and a decrease in the rate “at which hybridization has spread upstream in the drainage.”
“Although genetically pure westslope cutthroat trout will likely continue to be lost due to hybridization with rainbow trout in the interconnected Flathead River system over time,” the environmental assessment concludes, “information from suppression efforts so far indicate that FWP may be effective at reducing the rate and magnitude of that loss.”
The environmental assessment draft can be found at fwp.mt.gov/news/publicNotices/environmentalAssessments/restorationAndRehab/pn_0113.html. For questions or comments, contact FWP fisheries biologist Amber Steed at (406) 751-4541 or by email at [email protected].