Banks Lake Fish Survey (Grant County) September 2000

Banks Lake (Grant County) was surveyed by the Washington Department of Fish and Wildlife (WDFW) Warmwater Fish Enhancement Program and by the Inland Fish Investigations Unit from September 25-29, 2000. Nearshore and offshore surveys were conducted concurrently and are reported here in sections 1 and 2, respectively. For the littoral zone survey, a total of 140, 400 meter sections (32% of the shoreline) were sampled using boat electrofishing, gill netting, and fyke netting. Seventeen species, plus one additional family (Cottidae), were collected within the littoral zone of the reservoir. Smallmouth bass (Micropterus dolomieu) were the most abundant fish species comprising 40% (numerically) of the sample, followed by lake whitefish (Coregonus clupeaformis) (15%) and sculpin (12%). Lake whitefish had the highest biomass at 35% (by weight), followed by carp (Cyprinus carpio) (31%) and smallmouth bass (17%). Catchper- unit-effort (CPUE) by boat electrofishing was highest for smallmouth bass (71 fish/hour), followed by sculpin (25 fish/hour) and yellow perch (Perca flavescens) (11 fish/hour). CPUE for gill nets was highest for lake whitefish (7 fish/hour), smallmouth bass (2 fish/hour), and carp (1 fish/hour). CPUE by fyke net was highest for yellow perch (0.85 fish/hour), brown bullhead (Ameiurus nebulosus) (0.20 fish/hour), and black crappie (Pomoxis nigromaculatus) (0.15 fish/hour). Smallmouth bass, walleye (Stizostedion vitreum), and yellow perch showed slow growth and had low condition factors, when compared to the national 75th percentile averages. Slow growth and low condition factors of smallmouth bass were most likely due to overcrowding or inter- and intra-specific competition. Growth and condition factors of largemouth bass (Micropterus salmoides), black crappie, and pumpkinseed sunfish (Lepomis gibbosus) were above average when compared to other Washington lakes; however, CPUE for these species was low suggesting limited successful recruitment into the fishery. Small sample sizes collected for these three species made it difficult to know whether there was sampling bias related to gear type, fish distribution, or if limited suitable habitat, competition, and predation kept densities low. Yellow perch and walleye both showed good recruitment of young-of-year fish with 78% and 70% of the catch, respectively; however, low condition factor of yellow perch and walleye may have been due to interspecific competition with smallmouth bass. Limnological data in the southern section showed homogenous vertical profiles for all parameters collected, with a mean temperature of 15.8°C, and dissolved oxygen levels averaging 7.8 mg/l throughout the water column. In the northern section, thermal stratification occurred at 20-25m with epilimnetic conditions consistent with the southern site, but with cold temperatures (4.7°C) and low dissolved oxygen (1.7 mg/l) conditions in the hypolimnion. The offshore survey revealed a high abundance of lake whitefish occupying all depths of the reservoir. Lake whitefish dominated the species composition (79%), followed by walleye (11%). Kokanee salmon and rainbow trout were only a minor (1.9% each) portion of the offshore species composition. To better understand and manage the Banks Lake warmwater fishery, biologists will need to expand the survey to include angler creel interviews, limnological sampling in multiple locations, shoreline habitat analysis, population estimation through mark and recapture studies, as well as an indexing protocol for popular game fish species (i.e., walleye and bass). Currently, the Banks Lake Fishery Evaluation Project (BLFEP; WDFW), funded by Bonneville Power Administration, has begun extensive seasonal surveys of Banks Lake (Lewis et al. 2002; Polacek et al. 2003). Sampling includes a creel survey, water quality, primary and secondary productivity, littoral and limnetic fish surveys, mark and recapture studies, habitat analysis of the shoreline, and entrainment. Additionally, the WDFW Warmwater Program began annual fall walleye index netting (FWIN) in October of 2001. These studies will provide the necessary information to understand the fishery and be able to effectively provide management recommendations for catch rates, bag and slot limits, and stocking strategies to better manage fish populations within Banks Lake. Therefore, this report will not include management recommendations; rather, it will serve as a starting point for the more extensive studies that will follow.