– We studied diel microhabitat use at the focal point of age‐0 bull trout, Salvelinus confluentus, in Indian Creek, Washington during mid‐summer and fall of 1997. Microhabitat variables included water depth and velocity, distance from the stream bottom, habitat and refuge use, substrate type, and substrate embeddedness. Age‐0 fish were located over fines and gravel substrates in shallow, low‐velocity water near stream margins, but were located in shallower water at night. Bull trout were highly associated with loose substrate, and used the substrate interstices for refuge cover. Diurnal bull trout counts decreased and no age‐0 fish were observed after 15 September at water temperatures below 6.1 °C. Nocturnal counts remained relatively constant throughout the study. Our results suggest that age‐0 bull trout surveys be conducted at night when summer water temperatures begin to decline.
. 2018. Trophic compression of lake food webs under hydrologic disturbance. Ecosphere 9(6):e02304. 10. 1002/ecs2.2304 Abstract. The need to protect biostructure is increasingly recognized, yet empirical studies of how human exploits affect ecological networks are rare. Studying the effects of variation in human disturbance intensity from decades past can help us understand and anticipate ecosystem change under alleviated or amplified disturbance over decades to come. Here, we use stable isotopes and an innovative analytical approach to compare the food webs of two akin lake ecosystems subject to disparate water use regimes, a pervasive, yet unappreciated stressor. We show that intensive water use (persistent, early season, rapid lake-level drawdown) can compress trophic diversity by 46%, necessitating reorganization of biostructural elements configuring lake food webs. Compression occurred over the d 13 C axis indicating erosion of basal trophic diversity, but food chain length remained intact over the period and intensity of disturbance examined. This study demonstrates the potential for water use, like other disturbances (warming, eutrophication, and invasive species), to mute opportunity for benthic-pelagic coupling and benefits to lake food webs and the inherent capacity of lake ecosystems to adapt to stress. Trophically compressed lakes may be less able to adapt to intensified water use.
The Washington Department of Fish and Wildlife implemented the Banks Lake Fishery Evaluation Project (BLFEP) in September 2001 with funds from the Bonneville Power Administration. Fiscal Year (FY) 2001 of the BLFEP was used to gather historic information, establish methods and protocols, collect limnology data, and conduct the first seasonal fish surveys. FY 2002 was used to continue seasonal fish and lakewide creel surveys and adjust methods and protocols as needed. Water quality parameters were collected monthly from February to May and bi-monthly from June to August. Banks Lake water temperatures began to increase in April and stratification was apparent by June at all 3 limnology collection sites. By late August, the thermocline had dropped to nearly 20 meters deep, with 16-17 °C temperatures throughout the epilimnion. Dissolved oxygen levels were generally above 10 mg/L until August when dissolved oxygen dropped near or below 5 mg/L below 20-meters deep. Secchi depths ranged from 2.5-8 meters and varied by location and date. Nearshore and offshore fish surveys were conducted in October 2002 and May and July 2003 using boat electrofishing, fyke net, gill net, and hydroacoustic surveys. Yellow Perch Perca flavescens (32 %) and cottid spp. (22 %) dominated the nearshore species composition in October; however, by May yellow perch (12 %) were the third most common species followed by smallmouth bass Micropterous dolomieui (34 %) and lake whitefish Coregonus clupeaformis (14 %). Lake whitefish dominated the offshore catch during October (78 %) and May (81 %). Fish diet analysis indicated that juvenile fishes consumed primarily insects and zooplankton, while adult piscivores consumed cottids spp. and yellow perch most frequently. For FY 2002, the following creel statistics are comprehensive through August 31, 2003. The highest angling pressure occurred in June 2003, when anglers were primarily targeting walleye and smallmouth bass. Boat anglers utilized Steamboat State Park more frequently than any other boat ramp on Banks Lake. Shore anglers used the rock jetty at Coulee City Park 76 % of the time, with highest use occurring from November through April. An estimated total of 11,915 (±140 SD) smallmouth bass, 6,412 (±59 SD) walleye, 5,470 (±260 SD) rainbow trout, and 1,949 (±118 SD) yellow perch were harvested from Banks Lake in FY 2002. Only 3 kokanee were reported in the catch during the FY 2002 creel survey. In the future, data from the seasonal surveys and creel will be used to identify potential factors that may limit the production and harvest of kokanee, rainbow trout, and various spiny-rayed fishes in Banks Lake. The limiting factors that will be examined consist of: abiotic factors including water temperature, dissolved oxygen levels, habitat, exploitation and entrainment; and biotic factors including food limitation and predation. The BLFEP will also evaluate the success of several rearing and stocking strategies for hatchery kokanee in Banks Lake.i AcknowledgementsWe thank the Bonneville Power ...
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