–  The continuous observation of salmon behaviour in some wild environments can be extremely difficult. We recorded spawning behaviour of female chum salmon (Oncorhynchus keta) in the field simultaneously using visual observation and fish‐borne data loggers with two‐axis accelerometer sensors. Using only acceleration records, behaviours were successfully classified into the eight well‐known components of spawning behaviour: swimming, nosing, exploratory digging, nest digging, probing, oviposition, covering and post‐spawning digging. To understand how the female chum salmon modulates spawning behaviours in relation to changes in environmental conditions, we compared the behaviours of salmon during normal flow of clear water to those of salmon during the heavy flow of turbid water after a storm. Salmon in the normal flow showed all eight behaviours, whereas salmon in the heavy flow showed only three behaviours: swimming, nosing and exploratory digging. The proportion of time spent on swimming was greater in the heavy flow than in the normal flow (mean of 98.47% vs. 92.84%). Moreover, the proportion of tail beating in swimming was greater in the heavy flow (77.86%) than in the normal flow (15.63%). Our results indicate that the behaviour of female chum salmon was strongly affected by the heavy flow of turbid water after a storm. The recording of accelerations is a promising method for clarifying the spawning behaviour of salmonids in the wild where continuous visual observation is too difficult.

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The tail beat and activity behavior of four captive Japanese flounder Paralichthys olivaceus, were monitored with acceleration data‐loggers while the fish swam in an aquarium. Depth, swimming speeds and two‐axis acceleration data were collected continuously for approximately 20 h per fish. Simultaneously, the swimming behaviors of the fish were filmed at different angles. Using the specific characteristic of the acceleration profiles, in tandem with other types of data (e.g. speed and depth), four behavioral patterns could be distinguished: (i) ‘active’ swimming; (ii) burying patterns; (iii) ‘inactive’ gliding; and (iv) lying on the bottom. Tail beat frequency ranged from 1.65 ± 0.47 to 2.04 ± 0.25 Hz (mean ± SD; n = 4). Using the relationship between tail beat frequency and swimming speed, the ‘preferred’ swimming speed of the fish was estimated to be between 0.6 and 1.2 body lengths (BL)/s. Additionally, fish rarely swam faster than 1.2 BL/s. This study shows that the acceleration data‐loggers represent a useful and reliable system for accurately recording the tail beat of free‐ranging fish and estimating flatfish behavior.

A recently developed motion detector (acceleration data‐logger), based on acceleration measurements, was used to monitor the swimming behavior of two free‐swimming captive rainbow trout Oncorhynchus mykiss in an aquaculture net cage. Depth, swimming speeds and two‐direction acceleration data were collected continuously for approximately 20 h per fish. To define relationships between swaying acceleration profiles and tail beat activity of rainbow trout, the tail beat activity of trout was monitored using a video camera in a small tank with the simultaneous use of the acceleration data‐logger. During steady swimming, there were sharp, distinct peaks of swaying acceleration. When compared with the data from the video camera, the frequency of swaying acceleration was synchronized with the sequences of swimming activity. In addition, the tail beat frequency of the fish could be identified within the cycle of swaying acceleration during steady swimming phases. Mean tail beat frequency was 1.27 ± 0.40 and 1.40 ± 0.5 Hz (mean ± SD). Using the relationship between tail beat frequency and swimming speed, the ‘preferred’ swimming speed of trout was estimated to be between 0.48 and 0.58 body length (BL)/s, and trout rarely swam in excess of 2.0 BL/s. The present study shows that acceleration data‐loggers used to record spontaneous measurements of swimming speed and tail beat activity represent a useful and reliable system for accurately estimating both the rate of activities and movements of free‐ranging fish.