Hydroacoustic and Gill Net Assessment: Banks Lake, Washington
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Hydroacoustic and Gill Net Assessment Banks Lake, Washington Annual Report 2001 - 2002 February 2007 DOE/BP-00005860-3 This Document should be cited as follows: Baldwin, Casey, Matt Polacek, "Hydroacoustic and Gill Net Assessment; Banks Lake, Washington", 2001-2002 Annual Report, Project No. 200102800, 34 electronic pages, (BPA Report DOE/BP-00005860-3) Bonneville Power Administration P.O. Box 3621 Portland, OR 97208 This report was funded by the Bonneville Power Administration (BPA), U.S. Department of Energy, as part of BPA's program to protect, mitigate, and enhance fish and wildlife affected by the development and operation of hydroelectric facilities on the Columbia River and its tributaries. The views in this report are the author's and do not necessarily represent the views of BPA. Hydroacoustic and Gill Net Assessment of Banks Lake, Washington 2002 By Casey Baldwin and Matt Polacek Washington Department of Fish and Wildlife Science Division Ecological Investigations Unit Banks Lake Fishery Evaluation Project A Supplemental Technical Report to the 2001-2002 Banks Lake Annual Report; (DOE/BP-00005860-1). Project # 2001-02800 Contract # 00005860 July 2004 Abstract The Banks Lake Fishery Evaluation Project (BLFEP) was created in 2001 with funds from the Bonneville Power Administration. The overall objective of the project was to maximize the Banks Lake fishery by determining the factors that limit the recruitment of hatchery-stocked kokanee, rainbow trout, and panfish. A series of objectives were identified to test hypotheses related to the decline of the kokanee and panfish fisheries in Banks Lake. The methodologies selected for monitoring the populations and determining limiting factors included surveys of both the littoral and limnetic zones of the reservoir, where species composition can vary dramatically. Factors for decline being examined include predation, competition, over-harvest, entrainment, productivity, and habitat quality and quantity. The purpose of this survey was to estimate the species composition, distribution, and abundance of the limnetic fish community of Banks Lake using hydroacoustics and gill nets. Surveys were conducted in the spring and summer to test for differences in seasonal distribution and efficacy of the survey gear to establish a time period for conducting annual surveys for trend monitoring. Whitefish dominated the limnetic gill net species composition by weight (95%, both months) and number (83% July and 88% May). In May, relatively few fish were distributed deeper than 8 m in transects 12-18 at the South end of the reservoir and low densities were common for the deepest depth strata (16-24 m). In July, most fish were in the deepest depth strata available, 16-24 m throughout most of the reservoir. However, in transect 7 (Devils Lake Embayment) where deeper depths were available (54 m), many acoustic fish targets were also suspended mid-water in the 24-32 m depth strata. Acoustic target distribution varied by depth and location within and between surveys; however, the reservoir-wide mean fish density was not significantly different in May and July. The abundance estimate for acoustic fish targets between 100-800 mm was 1.3 x106 fish (± 0.45-0.65 x106) during both months. The middle portion of the reservoir (near Steamboat Rock) had the highest density of fishes during both seasons. Additionally, in July, fish were concentrating near the North Dam (transect 1) where cool water was being pumped in from Lake Roosevelt and in Devil’s Lake Embayment (transect 7) where deeper bottom depths offered a larger volume of cool water. These areas represent potential cool water refuge for salmonids. At the North end, near limnology site LIM1 and hydroacoustic transects 1 and 2, there was only one gill net set in July and it caught a rainbow trout near the surface. The rainbow trout net pens are released in this area in May-June each year, so it is possible that high abundance of acoustic targets near the surface were recently released rainbow trout. Unfortunately, the water temperature at LIM1 increased from 16 oC in July, to 19 oC in August, thereby eliminating this area as a potential thermal refuge for kokanee in late-summer. Due to the deeper vertical distribution of fish in July, we recommend that the mid-summer period continue to be used for assessing limnetic fish distribution and abundance. Hydroacoustic and Gill Net Assessment of Banks Lake, Washington 2002 ii Acknowledgements We thank the Bonneville Power Administration for funding the project, and the Northwest Power Planning Council, Columbia Basin Fish and Wildlife Authority, Independent Scientific Review Panel, and R. Morinaka (BPA) for approving and providing input and suggestions during development of the research plan. We thank D. Burgess (WDFW) and the Moses Lake research team for assistance during fish sampling. Dr. R. Black of Eastern Washington University for assistance with the limnology sampling plan and K. Knuttgen for research and summary of historical surveys of Banks Lake. Additional fieldwork or planning assistance was contributed by K. Knuttgen, J. Korth, J. McLellan, A. Smith, J. Kiesel, and H. Woller. Hydroacoustic and Gill Net Assessment of Banks Lake, Washington 2002 iii Table of Contents Abstract............................................................................................................................... ii Acknowledgements............................................................................................................ iii Table of Contents...............................................................................................................iv List of Tables .......................................................................................................................v List of Figures.................................................................................................................... vi Introduction..........................................................................................................................1 Study Area ...........................................................................................................................1 Methods................................................................................................................................2 Hydroacoustic Density and Distribution.........................................................................2 Gill Net Surveys..............................................................................................................5 Limnetic Fish Abundance...............................................................................................5 Abiotic Conditions..........................................................................................................6 Results..................................................................................................................................6 Hydroacoustic Density and Distribution.........................................................................6 Gill Net Surveys............................................................................................................10 Limnetic Fish Abundance.............................................................................................10 Abiotic Conditions........................................................................................................18 Discussion..........................................................................................................................18 References..........................................................................................................................25 Hydroacoustic and Gill Net Assessment of Banks Lake, Washington 2002 iv List of Tables Table 1. Species composition by number, weight and the minimum and maximum lengths of fish captured in offshore gill nets on Banks Lake, WA for May and July 2002 ........................................................11 Table 2. Effort (net nights), catch and catch per unit effort by gear type for fish captured in the main lake basin during May and July and in the Devil’s Lake embayment in July.....................................................12 Table 3. Abundance and Density (fish/ha) of all fish targets and specific size classes of fish targets in Banks Lake Washington, 2002. Length estimates were generated by converting target strength (dB) to total length (mm) using an equation from (Love 1971) ......................16 Table 4. Species-specific abundance estimates of limnetic fishes (~100- 800 mm TL) in Banks Lake, Washington in May and July 2002. Estimates were generated through mobile hydroacoustics and gill net surveys; error bounds were not estimated for percent species composition (% Spp) so the 2 SE only incorporates variance based on the acoustic estimate..............................19 Hydroacoustic and Gill Net Assessment of Banks Lake, Washington 2002 v List of Figures Figure 1. Map of Banks Lake, WA showing locations of hydroacoustic transects and limnology sites where data was collected in July of 2002. The southern most transect was not surveyed due to insufficient nighttime hours ...............................................................................3 Figure 2. Density of target-tracked fish for 16 hydroacoustic transects in May 2002 on Banks Lake, Washington. Transects three and four were not analyzed due to shallow depths for the vertical transducer and excessive noise for the horizontal transducer.