Population suppression of the invasive channel catfish Ictalurus punctatus in the Seta River, outflowing from Lake Biwa, Japan

Abstract

　The channel catfish Ictalurus punctatus has become established below the Setagawa weir, built to prevent the Lake Biwa water system flooding into the Seta River, the only river outflowing from Lake Biwa. The channel catfish is believed to naturally migrate upstream toward Lake Biwa, leading to targeted removal through eradications and surveys (using longlines) conducted above the weir since 2019. To evaluate the effectiveness of such a control practice, changes in capture efficiency, individual fish body length, and annual numbers of newly produced juvenile were analyzed. The results indicated that continued longline fishing suppressed the population, as evidenced by declining capture efficiency, increasing periods of zero captures of juveniles or adults, yearly decreases in the number of newly produced juveniles, and lower capture rates of individuals thought to have resulted from the latter. The findings confirmed the effectiveness of longline fishing in controlling channel catfish, and the necessity of continuing such capture and removal practices to prevent further invasions of the species into Lake Biwa.