Acoustic zone monitoring to quantify fine-scale movements of aquatic animals in a narrow water body

Fine-scale spatial acoustic telemetry, including hyperbolic and centre-of-activity localisation, is widely used to provide insight into the ecology of aquatic animals. However, these positional telemetry systems require numerous receivers, even for limited study areas such as narrow rivers, creeks, and canals, where tagged animals are typically monitored by receivers deployed at locations of particular interest or across a water body (acoustic gate). This paper proposes an acoustic zone monitoring method, which only uses a few acoustic receivers to estimate a zone used by a tagged fish in narrow water bodies. The effectiveness of the proposed method was verified by performing stationary and moving tests and by monitoring the movements of an invasive species in Japan, the channel catfish Ictalurus punctatus . Eight acoustic receivers were deployed 100–270 m apart along the river, with each zone having a length of 100–190 m. The proposed method provided accurate estimates in the inner and outermost zones of the eight stationary transmitters (100%, number of estimates: 1118 ± 419) and of a single transmitter towed by a boat (99.1%, number of estimates: 111/112). By contrast, centre-of-activity localisation estimated positions around the centre of the receiver array, and hyperbolic localisation was unable to provide positions because of an almost-straight-line array of receivers. The proposed zone monitoring method provided more accurate movement estimates of the tagged catfish. The method can cover an extended area using a limited number of receivers at a fine scale and be applied to initially identify the predominant habitats and distribution used by target species in the new study sites.