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<br />001558 <br /> <br />Journal ofFish Biology (2004) 65, 1643-1652 <br />doi: 1 0.1111jj.1 095-8649 .2004.0057 5.x, available online athttp://www.blackwell-synergy.com <br /> <br />Comparison of electrofishing and trammel netting <br />variability for sampling native fishes <br /> <br />C. P. PAUKERT <br /> <br />U.S. Geological Survey, Grand Canyon Monitoring and Research Center, Southwest <br />Biological Science Center, 2255 North Gemini Drive, Flagstaff, AZ 86001, U.S.A. <br /> <br />(Received 7 May 2003, Accepted 14 September 2004) <br /> <br />The variability in size structure and relative abundance (CPUE; number of fish ;:::200 mm total <br />length, Lr, collected per hour of electrofishing or trammel netting) of three native Colorado <br />River fishes, the endangered humpback chub Gila cypha, flannelmouth sucker Catostomus <br />latipinnus and bluehead sucker Catostomus discobolus, collected from electrofishing and tram- <br />mel nets was assessed to determine which gear was most appropriate to detect trends in relative <br />abundance of adult fishes. Coefficient of variation (CV) of CPUE ranged from 210 to 566 for <br />electrofishing and 128 to 575 for trammel netting, depending on season, diel period and species. <br />Mean CV was lowest for trammel nets for humpback chub (P=0'004) and tended to be lower <br />for flannelmouth sucker (P= 0,12), regardless of season or diel period. Only one bluehead <br />sucker >200mm was collected with electrofishing. Electrofishing and trammel netting CPUE <br />were not related for humpback chub (r= -0'32, P= 0,43) or flannelmouth sucker (r= -0'27, <br />P = 0.46) in samples from the same date, location and hour set. Electrofishing collected a higher <br />proportion of smaller (<200mm Lr) humpback chub (P < 0'001), flannelmouth suckers <br />(P < 0'001) and bluehead suckers (P < 0,001) than trammel netting, suggesting that conclusions <br />derived from one gear may not be the same as from the other gear. This is probably because these <br />gears fished different habitats, which are occupied by different fish life stages. To detect a 25% <br />change in CPUE at a power of 0.9, at least 473 trammel net sets or 1918 electrofishing samples <br />would be needed in this 8 km reach. This unattainable amount of samples for both trammel <br />netting and electrofishing indicates that detecting annual changes in CPUE may not be practical <br />and analysis oflong-term data or stock assessment models using mark-recapture methods may be <br />needed to assess trends in abundance of Colorado River native fishes, and probably other rare <br />fishes as well. <l:l 2004 The Fisheries Society of the British Isles (No claim to original US government works) <br /> <br />Key words: bluehead sucker; Colorado River; flannelmouth sucker; humpback chub; sampling. <br /> <br />INTRODUCTION <br /> <br />Fisheries researchers need precise estimates of fish population statistics (e.g. <br />abundance and size structure) to adequately assess the status of fish popula- <br />tions. Previous research has suggested that gear bias is evident for many fish <br />species and habitats (Hubert, 1996; Reynolds, 1996). Relative abundance and <br />size structure indices are often different between gear types (Guy et al., 1996; <br /> <br />Present address: U.S. Geological Survey, Biological Resources Division, Kansas Cooperative Fish and <br />Wildlife Research Unit, 205 Leasure Hall, Division of Biology, Kansas State University, Manhattan, KS <br />66506, U.S.A. TeL: +I 7855326522; fax: +I 7855327159; email: cpaukert@ksu.edu <br /> <br />1643 <br /><l:l 2004 The Fisheries Society of the British Isles (No claim to original US government works) <br />