1. The Calapooia River in western Oregon supports a small winter steelhead trout (Oncorhynchus mykiss) population and historically supported spring Chinook salmon (Oncorhynchus tshawytscha). Early timber harvesting removed the riparian forest, and log transportation practices simplified the channel. Those disturbance legacies continue to affect fish habitat by limiting shade and channel complexity, complicating conservation efforts.2. To evaluate juvenile salmonid rearing potential, macroinvertebrate drift, thermal regime and physical habitat were measured at eight sites in 24 km of the upper river during late summer baseflow.3. Overall physical habitat was simple, with few functioning instream structures or pools. During the 22-day drift study, flows declined and maximum site stream temperatures ranged from 23.1°C at the lower end to 16.4°C 24 km upstream.4. Macroinvertebrate drift concentrations ranged from 0.7-13.7 ind. m −3 with biomasses from 0.02-1.23 mg m −3 . Drift concentration biomass was higher upstream (P = 0.006) than downstream and declined overall (P < 0.001) during the study. Drift biomass was dominated by five taxon groups -Baetis tricaudatus, Calineuria californica, Hesperoperla pacifica, Simulium spp., and Chironomidae, which were 65% of total biomass. During twilight, total biomass and biomass of B. tricaudatus, Simulium spp., and Chironomidae (both larvae and adults) were higher. 5. Total drift declined dramatically over the study period owing to decreases in drift concentration and a 58% decline in discharge, greatly reducing overall drift and available food resources for juvenile-rearing salmonids.6. The upper catchment, both with cooler temperatures and higher food availability, provided the best conditions for juvenile anadromous salmonids to survive late summer conditions. Conservation consequences of climate change-induced alterations in flow and temperature may further affect habitat quality for juvenile salmonids in this catchment in the coming decades.
Off-channel habitats such as backwaters and side channels provide important nursery and feeding habitats for native fishes of the Missouri River, including the endangered pallid sturgeon (Scaphirhynchus albus). We mapped backwaters, side channels, and secondary channels (hereafter referred to as "other channels") on the Missouri River below Fort Peck dam for 1956/57, 1980, 2009, 2011, and 2013. We compared the total number of mapped features and mean length, area, and perimeter of the features between 1956/57 (hereafter referred to as 1956) and 2013 to determine if there are discernable trends in availability of off-channel habitats to native fish. Relative to 1956, 2013 had less total area of off-channel habitat available, as well as a smaller mean area, suggesting a loss of suitable habitat for the pallid sturgeon and other native fishes of the Missouri River below Fort Peck dam. The large flood event in 2011 may have scoured sediments that accumulated during low flow years of the mid-2000s, leading to channel incision and loss of connection between off-channel habitat and the main river channel.
Off-channel habitats such as backwaters and side channels provide important nursery and feeding habitats for native fishes of the Missouri River, including the endangered pallid sturgeon (Scaphirhynchus albus). We mapped backwaters, side channels, and secondary channels (henceforth referred to as "other channels") on the Missouri River between Fort Peck dam and the North Dakota state line for 1956/57, 2009, and 2011, the latter of which was a flood year. We compared the total number of mapped features and mean length, area, and perimeter of the features between 1956/57 and 2009. Each habitat type increased significantly in total number between 1956/57 and 2009. Although we observed an increase in the total number of offchannel habitats between 1956/57 and 2009, the average area of each type of habitat decreased by 50%, which suggests that these areas may be unsuitable for the pallid sturgeon and other native fishes of the Missouri River below Fort Peck dam. A large flood event in 2011 may have been a significant enough event to restore these habitats; examination of post-flood imagery may help answer that question and guide restoration and recovery efforts for the pallid sturgeon. v ACKNOWLEDGMENTSThis project was funded by the Montana Fish, Wildlife, and Parks. We would like to thank Andy Brummond in the FWP Lewistown Area Resource Office for his invaluable support and guidance during this process. Karen Newlon and Linda Vance of MTNHP provided useful comments on an earlier draft of this report. Any errors or omissions in the report are entirely the responsibility of the authors.
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