1The Miyagi Prefectural Izunuma-Uchinuma Environmental Foundation, Kurihara, Miyagi 989-5504, 2Society for Shinaimotsugo Conservation, Osaki, Miyagi 989-4102, 3Department of Aquatic Bioscience, Tokyo University of Agriculture, Faculty of Bioindustry, Abashiri, Hokkaido 099-2493, 4School of Marine Biosciences, Kitasato University, Ofunato, Iwate 022-0101, Japan
The attractiveness of conspecific individuals as decoys was investigated in Lakes Izunuma and Kejonuma in northern Japan to develop a new effective method for extermining the bluegill Lepomis macrochirus on the basis of their aggregation behavior. Two types of trap—empty traps (control) and traps with bluegill individuals as decoys (treatment)—were set up in these lakes, and the catch-per-unit efforts (CPUEs) of the treatment and control traps were compared. The CPUEs of the treatment traps were higher than those of the control traps in Lake Izunuma where bluegill density is low; this finding suggests that the decoys attracted the conspecific fish. In Lake Izunuma, the treatment traps were introduced to eradicate the alien fish and were used for 2 months, resulting in a 1.86 times increase in the total catch of bluegill compared with conventional methods. These results showed the attractive effects of the conspecific bluegill as decoys, which can thus be used for effectively controlling the bluegill population. On the other hand, the decoys did not attract the fish in Lake Kejyonuma where bluegill density is high. Thus, the attractiveness of the decoy is affected by the density of the bluegill.