Comparison of Electrofishing and Gill Netting for Sampling Gizzard Shad

Gill netting (mesh sizes from 13 to 64 mm) and electrofishing were conducted in April and October 1987-1989, to compare their utility for providing precise estimates of relative abundance and size structure of gizzard shad (Dorosoma cepedianum) populations in 2 Ozark impoundments. Catches of gizzard shad <120 mm were extremely variable for electrofishing and very low for gill netting and were excluded from further analysis. Electrofishing captured more gizzard shad ≥120 mm with less effort (68-339 fish/hour) than gill netting (2-48 fish/net day). However, neither method provided precise estimates of catch per unit effort (CPUE) for gizzard shad >120 mm; coefficients of variation ranged from 44% to 144% for electrofishing and 39% to 131% for gill netting. Sample sizes required for a CV8 (SE/mean) of 20% ranged from 5 to 52 for electrofishing runs and 5 to 43 sets for gill netting. There was no significant difference in CPUE between April and October for either gear. Neither mean CPUE nor mean length of gizzard shad ≥ 120 mm were correlated between the 2 gears (P > 0.64), indicating that the gears did not reveal similar trends in mean CPUE or length. Electrofishing captured a wider length range of gizzard shad; gill netting rarely caught gizzard shad < 180 mm.

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