No abstract

Longitudinal gradients of fish assemblage and habitat structure were investigated in the Kootenai River of northern Idaho. A total of 43 500‐m river reaches was sampled repeatedly with several techniques (boat‐mounted electrofishing, hoop nets and benthic trawls) in the summers of 2012 and 2013. Differences in habitat and fish assemblage structure were apparent along the longitudinal gradient of the Kootenai River. Habitat characteristics (e.g. depth, substrate composition and water velocity) were related to fish assemblage structure in three different geomorphic river sections. Upper river sections were characterized by native salmonids (e.g. mountain whitefish Prosopium williamsoni), whereas native cyprinids (peamouth Mylocheilus caurinus, northern pikeminnow Ptychocheilus oregonensis) and non‐native fishes (pumpkinseed Lepomis gibbosus, yellow perch Perca flavescens) were common in the downstream section. Overall, a general pattern of species addition from upstream to downstream sections was discovered and is likely related to increased habitat complexity and additions of non‐native species in downstream sections. Assemblage structure of the upper sections were similar, but were both dissimilar to the lower section of the Kootenai River. Species‐specific hurdle regressions indicated the relationships among habitat characteristics and the predicted probability of occurrence and relative abundance varied by species. Understanding fish assemblage structure in relation to habitat could improve conservation efforts of rare fishes and improve management of coldwater river systems. Copyright © 2015 John Wiley & Sons, Ltd.

River regulation alters the thermal regime of many freshwater ecosystems, and impoundments are known to negatively impact the recruitment of fluvial Burbot Lota lota populations. Some conservation programs in North America and Eurasia have begun to incorporate stocking of hatchery Burbot to mitigate extirpation risks. Anthropogenic modification of river temperatures and population structure has unknown implications for Burbot reproduction. This study evaluated the effects of elevated water temperatures and different maternal ages on spawning and embryo development of hatchery Burbot. Juveniles stocked downstream of a hydroelectric dam were found to naturally mature in a warmer postdam regime. The river‐adapted hatchery adults volitionally spawned in a broodstock facility at 2, 4, and 6°C. The spawning period spanned 18 d at 2°C but was shortened to 6−7 d at 4°C and 6°C. Survival of embryos to the eyed stage was 86.7, 47.9, and 0.1% at incubation temperatures of 2, 4, and 6°C, respectively. Embryo deformity increased dramatically between 4°C and 6°C. Young (age‐3) and old (age‐7 and older) females spawned 4−12 d later than 5‐ and 6‐year‐old females. Age‐3 females spawned smaller eggs, but no relationship was found between maternal age and embryo vital rates. It was concluded that juvenile stocking supplemented the abundance of reproductive adults in the highly altered ecosystem of the lower Kootenai River. Spawning temperatures above 4°C potentially underlie Burbot recruitment bottlenecks in systems affected by impoundments, climate warming, or other barriers to coldwater spawning habitat. Contraction of the spawning period by warmer temperatures, a truncated population age structure, or both could synchronize spawning to coincide with suboptimal conditions for normal embryo development.

In Idaho, Burbot Lota lota are endemic only to the Kootenai River, where they once provided an important winter fishery to the indigenous people and European settlers. This fishery and that of Kootenay Lake in British Columbia may have been the most robust Burbot fisheries in North America. However, the fishery in Idaho rapidly declined after the construction of Libby Dam by the U.S. Army Corps of Engineers in 1972, and it closed in 1992. Concomitant to the collapse in Idaho was the collapse of the Burbot fishery in Kootenay Lake and the Kootenay River. The operation of Libby Dam for hydroelectric power generation and flood control created major changes in the river's nutrient concentration, temperature, and seasonal discharge, particularly during the winter when Burbot spawn. Libby Dam operations were implicated as the major limiting factor to Burbot recruitment, giving rise to higher winter temperatures and widely fluctuating flows. Because the Burbot in the Kootenai River are at risk of demographic extinction, a conservation strategy was prepared to outline the measures necessary to rehabilitate the Burbot population to a self-sustaining level. The strategy indicated that operational discharge changes at Libby Dam are required during winter to provide suitable temperature and discharge conditions for Burbot migration and spawning. Studies recommend that the discharge at Bonners Ferry average 176 m 3 /s for a minimum of 90 d (midNovember through mid-February). Furthermore, preferred Burbot water temperatures of about 6 • C are necessary for migration and cooler temperatures of 1-4 • C for spawning. With each passing year, Burbot stock limitations increasingly constrain rehabilitation. Thus, coordination of intensive culture, extensive rearing, and pen rearing among the Kootenai Tribe of Idaho, the British Columbia Ministry of Environment, the University of Idaho's Aquatic Research Institute, and the Idaho Department of Fish and Game is important for restoration.

Burbot Lota lota movement and river discharge were studied in the Kootenai River, Idaho, U.S.A. and British Columbia, Canada, downstream of Libby Dam, Montana, U.S.A. A total of 24 adult burbot with transmitters were tracked from 1994 to 2000, for analysis of a travel distance of !5 km in 10 days termed 'stepwise movement'. Of 44 'stepwise movements', significantly greater movements during pre-spawning and spawning were observed when average daily discharges from Libby Dam were <300 m 3 s À1 , with a mean of 176 m 3 s À1 , similar to pre-dam conditions. Burbot travelled at a greater rate during all seasons (3Á36 km day À1 ) at discharges >300 m 3 s À1 (mean ¼ 1Á84 km day À1 ) than at discharges >300 m 3 s À1 but no difference was found for the pre-spawning and spawning period. Burbot that started 'stepwise movements' in low discharge conditions frequently stopped during low discharges. # 2005 The Fisheries Society of the British Isles