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Abstract
The health and welfare of farmed fish are highly dependent on environmental conditions. Under suboptimal conditions, the negative impact on welfare can cause changes in fish behaviour. Acoustic tags can provide high resolution and high frequency data to monitor fish positioning within the cage, which can be used to infer swimming behaviour. In this study, implanted acoustic tags were used to monitor the three-dimensional positioning of Atlantic salmon (Salmo salar) at a commercial farm in Nova Scotia, Canada. The one-month study period allowed the characterisation of background behaviour and changes in behaviour in relation to different environmental conditions, namely, water characteristics in terms of dissolved oxygen and temperature caused by the fall overturn, storm conditions, and feeding activity. The three-dimensional position of 15 fish was recorded using high temporal resolution (3 s). Fish movement was characterised by calculating four fish variables: distance from the centre of the cage [m], depth [m], velocity [ms−1], and turning angle [°]. The population swam in a counterclockwise swimming direction around 4 ± 2 m depth at an average speed of 0.61 ± 0.38 ms−1. After the fall overturn, the population moved significantly towards cage centre while decreasing velocity, and non-significant differences in depth and turning angle were observed. During feeding periods, a significant increase in depth and velocity, as well as a reduction in turning angle were observed. The storm event did not cause any significant change in the four fish variables. While some of the behavioural changes were difficult to assess with respect to causation, the high resolution, high frequency data provide unique detailed positioning information to further our understanding of the swimming behaviour of farmed fish.
Highlights
Farmed Atlantic salmon are subject to a variety of environmental stressors, including diseases, marine heatwaves, harmful algal blooms, and anoxic events
There are a variety of external variables available to evaluate as determinants of behaviour including oxygen, temperature, and wind
Some of the changes in defined behaviours were subtle and difficult to assess with respect to causality
Summary
Farmed Atlantic salmon are subject to a variety of environmental stressors, including diseases, marine heatwaves, harmful algal blooms, and anoxic events. Since fish are highly mobile, their ability to change positioning within the net pen can be critical in Environmental Events on Salmon Behaviour stress avoidance. Four variables were examined in individual fish including (a) distance from centre of the net pen [m], (b) swimming depth [m], (c) swimming velocity [ms−1], and (d) turning angle [◦] (Equations 1–4; Figure 2). Heatmaps of horizontal fish position based on % of observations in a given location (Figure 3) show examples of the two emphasised individuals. In both cases, the maximum density of observations is
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