実験河川におけるエレクトリックショッカーによる6魚種の捕獲効率

We examined electrofishing catchability of six most abundant fish species in experimental stream A in the Aqua Restoration Research Center in Gifu, Japan. The electrofishing catchability can be defined as the total catch obtained by electrofishing divided by the sum of catches obtained by electrofishing and by chasing into D-shaped nets. The six species were classified into high catchability species (more than 80% of the catch) (Plecoglossus altivelis altivelis, Misgurnus anguillicaudatus, and Cobitis sp.) and low catchability species (less than 80% of the catch) (Zacco platypus, Gnathopogon elongatus elongatus, and Rhinogobius sp.). Two age groups were confirmed in each of the low catchability species by estimation of the fish size (total length mm). Each peak of the first and the second age groups were positioned less and more than 40 mm, respectively. The catchability of the first age group of Z. platypus as a swimming fish was significantly lower than the second age group of the species. The catchability range of Rhinogobius sp., a benthic fish, was lower (24%-67%) than that of Z. platypus and G. elongatus elongatus values. Furthermore, the catchability of the second age group of Rhinogobius sp. was lower than that of Z. platypus. These results suggest that electrofishing alone is not a suitable capture method because its capture rates for small swimming fish < 40 mm and for all sizes of benthic fishes are low. Therefore, electrofishing should be used along with the D-shape nets and the small swimming fishes and benthic fishes should be chased into the nets. Additionally, we recommend that further studies are required to determine not only the catchability for each of these species but also to study damages by electrofishing to fish under various voltage, pulse, and environmental conditions.