Lemhi River, ID Intensively Monitored Watershed Project - Anadromous Fish Distribution and Productivity Response to Watershed Restoration

The Lemhi River located in East-central Idaho is substantially influenced by agriculture. Irrigation practices severed the surface water connection of 28 of 30 major tributaries to the mainstem Lemhi River. Historical records document the value of many of these tributaries as spawning and rearing habitat for spring/summer Chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. mykiss). Railroad construction transformed the lower mainstem Lemhi River from an mostly unconfined channel to a fast-flowing linear reach. Simultaneously agricultural development resulted in the loss of the majority of the riparian corridor. The 2008 Biological Opinion on the Federal Columbia River Power System identified the need to improve the freshwater productivity of Chinook salmon and Steelhead in the Lemhi River by 4% and 7% respectively via implementation of habitat restoration measures. Restoration measures have included barrier removal, minimum in-stream flow targets, tributary reconnection, targeted in-stream habitat restoration (channel realignment), and reconnection of floodplain habitat. The ISEMP program was implemented in 2009 to assess the effectiveness of these restoration actions. We will present results-to-date on how these actions have altered the distribution of anadromous adults and juveniles and influenced survival. Long-term estimates of freshwater productivity will be presented as well as predictions of adult escapement.