Comparison of electrofishing and trammel netting variability for sampling native fishes

Abstract

The variability in size structure and relative abundance (CPUE; number of fish !200 mm total length, L T , collected per hour of electrofishing or trammel netting) of three native Colorado River fishes, the endangered humpback chub Gila cypha, flannelmouth sucker Catostomus latipinnus and bluehead sucker Catostomus discobolus, collected from electrofishing and trammel nets was assessed to determine which gear was most appropriate to detect trends in relative abundance of adult fishes. Coefficient of variation (CV) of CPUE ranged from 210 to 566 for electrofishing and 128 to 575 for trammel netting, depending on season, diel period and species. Mean CV was lowest for trammel nets for humpback chub (P ¼ 0Á004) and tended to be lower for flannelmouth sucker (P ¼ 0Á12), regardless of season or diel period. Only one bluehead sucker >200 mm was collected with electrofishing. Electrofishing and trammel netting CPUE were not related for humpback chub (r ¼ À0Á32, P ¼ 0Á43) or flannelmouth sucker (r ¼ À0Á27, P ¼ 0Á46) in samples from the same date, location and hour set. Electrofishing collected a higher proportion of smaller (<200 mm L T ) humpback chub (P < 0Á001), flannelmouth suckers (P < 0Á001) and bluehead suckers (P < 0Á001) than trammel netting, suggesting that conclusions derived from one gear may not be the same as from the other gear. This is probably because these gears fished different habitats, which are occupied by different fish life stages. To detect a 25% change in CPUE at a power of 0Á9, at least 473 trammel net sets or 1918 electrofishing samples would be needed in this 8 km reach. This unattainable amount of samples for both trammel netting and electrofishing indicates that detecting annual changes in CPUE may not be practical and analysis of long-term data or stock assessment models using mark-recapture methods may be needed to assess trends in abundance of Colorado River native fishes, and probably other rare fishes as well.

Sampling techniques for burbot in a western non‐wadeable river

“…A gear-specific effect on detection probabilities was apparent for juvenile and adult burbot for both seasons. The effect of gear on detection probabilities was not surprising given the long-established biases associated with different fish sampling techniques (Paukert 2004;Hetrick & Bromaghin 2010). For instance, Schloesser et al (2012) reported that detection probabilities for a number of Missouri River fishes were most influenced by sampling technique (i.e.…”

A Comparison of Modified Fyke Nets for Evaluating Fish Assemblages and Population Structure

“…For example, relative abundance (e.g., catch-per-unit-effort; CPUE) and size structure (e.g., proportional size distribution; PSD) estimates often vary seasonally Willis 1991, Pope and due to factors such as behavior (e.g., spawning) and growth of individuals throughout the year. Additionally, different sampling gears often capture individuals of different numbers and sizes of the same species (Guy et al 1996, Tate et al 2003, Paukert 2004. Similarly, differences in gear specifications (e.g., dimensions and mesh size) and materials (e.g., filament type, color) used to construct sampling gear can bias estimates, such as relative abundance, size structure, and species composition (Willis et al 1984, Henderson and Nepszy 1992, Gray et al 2005, Wanner et al 2010.…”

An initial assessment of sampling procedures for juvenile pallid sturgeon in the Missouri River downstream of Fort Randall Dam, South Dakota and Nebraska

“…Fisheries managers and researchers require unbiased estimates of fish population characteristics. Sampling techniques should provide a measure of relative abundance, and the fish captured should accurately reflect the size structure of the fish population (Guy et al., 1996; Colvin, 2002; Paukert, 2004). Sampling must also be standardized to obtain precise, unbiased estimates of fish population size and age structure and relative abundance (Allen et al., 1999).…”