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Abstract

Bio-logging and bio-telemetry are effective methods for monitoring the activity of aquatic animals. Tagging technology has recently advanced, and it is now possible to use tracking devices on small fish and multiple individuals. For species that live in schools such as small pelagic fish, analyzing the activity of multiple individuals may help to further our understanding of school activity in nature. In this study, we tracked the swimming depth of multiple individuals of schooling Pacific herring and examined whether the school’s characteristics and activity can be estimated from the individuals’ swimming depth in the laboratory and a set net experiment. In the laboratory, herring formed dense schools during the day and scattered at night. The change in swimming depth in four tagged individuals often synchronized. A high frequency of short vertical neighbor distance (VND: 0-0.5 m) for a long duration (> 200 s) was typical in dense schools. In contrast, scattered schools were typically reflected by a wide distribution of VND for a short duration. Therefore, some school characteristics and activity in the laboratory can be estimated by VND and duration. However, in the set net, the diurnal difference was only observed in the VND distribution, and school characteristics could not be estimated clearly. Herring school characteristics and activity are influenced by school density and external stimuli such as light intensity

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