Modified Sampling Design for Age-0 Fish Electrofishing at Beach Habitats

Abstract

Fright bias can cause misleading results when sampling age-0 fish in beach habitats. In this study, different sampling methods were tested to reduce fright bias. Experiments using video recordings demonstrated that efficiency was 13% for extension pole electrofishing (EPE), 47% for thrown anode electrofishing (TAE), and 100% for pre-positioned anode electrofishing (PAnE). We propose a modified PAnE design for sampling age-0 fish that would not be excessively time consuming. The modified PAnE sampling design was then tested against EPE, TAE, and fine-mesh seine netting (SN). We found that PAnE sampled significantly more species and individuals than EPE and TAE. Assemblage structure sampled by PAnE differed significantly from that sampled by EPE, TAE, and SN; the difference was more substantial relative to SN than to EPE or TAE. Assemblages sampled by EPE and TAE had a lower representation of common bleak Alburnus alburnus, white-fin gudgeons Gobio albipinnatus, common dace [also known as Eurasion dace] Leuciscus leuciscus, and roach Rutilus rutilus compared with PAnE. Assemblages sampled by SN had a lower representation of white-fin gudgeons, chub [also known as European chub] L. cephalus, common barbels Barbus barbus, and common nase Chondrostoma nasus compared with PAnE. No difference was found in length distributions of fish captured by PAnE and the other methods. Although the modified PAnE design demonstrated significantly reduced time consumption, it was still more time consuming than the other sampling methods. The apparent advantages of PAnE were its high relative efficiency (higher number of fish/min of sampling relative to the other methods) and its minimization of the bias and selectivity caused by the investigator's presence or action.