Determining the Effects of Environmental Events on Cultured Atlantic Salmon Behaviour Using 3-Dimensional Acoustic Telemetry

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.

Food anticipatory behaviour on European seabass in sea cages: activity-, positioning-, and density-based approaches

“…The electronic transmitters can be equipped with several sensors to yield a variety of information, including the depth, temperature, acceleration, and position of the individual fish. These data sources can be used in conjunction to draw conclusions about different behavioural or physiological states of the fish, as is the case with Atlantic salmon, which dominates as captive fish species where acoustic telemetry is used (Føre et al, 2011;Kolarevic et al, 2016;Føre et al, 2018b;Stockwell et al, 2021).…”

Recent advances in acoustic technology for aquaculture: A review

“…Furthermore, quantifying swimming activity can predict that the water quality environment may have changed. For example, both hypoxic and hyperoxic conditions result in a significant reduction in total activity in Atlantic salmon 32 ; swimming activity during crowding and delousing events are significantly higher than that recorded on the day before and after delousing activity 163 ; and temperature, pH and feed and light are also sensitive indicators of abnormal activity in aquatic organisms 164,165 . In addition to depth sensors and acceleration sensors as acoustic tags, the use of acoustic transmitters (such as electromyograms and heart rate) that can reflect the energy consumption of aquatic organisms will help to better understand the metabolic costs of different activities 166,167 .…”

“…For example, both hypoxic and hyperoxic conditions result in a significant reduction in total activity in Atlantic salmon 32 ; swimming activity during crowding and delousing events are significantly higher than that recorded on the day before and after delousing activity 163 ; and temperature, pH and feed and light are also sensitive indicators of abnormal activity in aquatic organisms. 164,165 In addition to depth sensors and acceleration sensors as acoustic tags, the use of acoustic transmitters (such as electromyograms and heart rate) that can reflect the energy consumption of aquatic organisms will help to better understand the metabolic costs of different activities. 166,167 Moreover, acoustic transmitters allow real-time wireless transmission of data to users through hydrophone receivers and realtime monitoring using wired receivers, 17,168 enabling fish farmers to monitor changes in group behaviour and respond immediately.…”

Offshore aquaculture of finfish: Big expectations at sea

“…However, provided that they have sufficient depth range in a cage, Atlantic salmon can move to deeper waters during a storm, as the power of waves decreases in the water column. Contrary to this, an acoustic telemetry study on fish movement inside an Atlantic salmon sea cage detected no changes in behaviour (distance from the centre of the cage [m], depth [m], velocity [m/s], and turning angle [°]) during a storm event 96 . Fish behaviour during a storm is complex and depends on the power and frequency of the waves, as well as the current speed and time of day.…”

“…Contrary to this, an acoustic telemetry study on fish movement inside an Atlantic salmon sea cage detected no changes in behaviour (distance from the centre of the cage [m], depth [m], velocity [m/s], and turning angle [°]) during a storm event. 96 Fish behaviour during a storm is complex and depends on the power and frequency of the waves, as well as the current speed and time of day. The objective of this behaviour is to minimise collision risk.…”