Fishing Technology Division, National Research Institute of Fisheries Engineering, Fisheries Research Agency, Kashima, Ibaraki 314-0421, Japan
Smallmouth bass Micropterus dolomieu is an introduced fish native to North America. This fish has been rapidly spreading its habitat in Japan recently due to illegal introductions. It is necessary to capture smallmouth bass efficiently to conserve the aquatic ecosystems. Field experiments were conducted in Lake Aoki to investigate the time zone during which the smallmouth bass were efficiently captured by gillnets, while reducing the bycatch of native fishes. Motion detectors and acceleration sensors were put on gillnets to record the time when fishes were captured. Motion detectors and acceleration sensors record the motion caused by fishes entangled on the gillnet. Fish capture time for each individual was estimated from these time-series data. Eighty-six percent of the smallmouth bass were captured from sunrise to sunset. On the other hand, 91 percent of the crucian carp Carassius sp. and 92 percent of the common carp Cyprinus carpio were captured from sunrise to sunset. It is possible to reduce the bycatch of fish such as crucian carp and common carp by soaking the gillnet in the daytime.