Abstract
Background: Climate change is leading to increased water temperatures and reduced oxygen levels at sea-cage sites, and this is a challenge that the Atlantic salmon aquaculture industry must adapt to it if it needs to grow sustainably. However, to do this, the industry must better understand how sea-cage conditions influence the physiology and behavior of the fish.Method: We fitted ~2.5 kg Atlantic salmon on the south coast of Newfoundland with Star-Oddi milli-HRT ACT and Milli-TD data loggers (data storage tags, DSTs) in the summer of 2019 that allowed us to simultaneously record the fish's 3D acceleration (i.e., activity/behavior), electrocardiograms (and thus, heart rate and heart rate variability), depth, and temperature from early July to mid-October.Results: Over the course of the summer/fall, surface water temperatures went from ~10–12 to 18–19.5°C, and then fell to 8°C. The data provide valuable information on how cage-site conditions affected the salmon and their determining factors. For example, although the fish typically selected a temperature of 14–18°C when available (i.e., this is their preferred temperature in culture), and thus were found deeper in the cage as surface water temperatures peaked, they continued to use the full range of depths available during the warmest part of the summer. The depth occupied by the fish and heart rate were greater during the day, but the latter effect was not temperature-related. Finally, while the fish generally swam at 0.4–1.0 body lengths per second (25–60 cm s−1), their activity and the proportion of time spent using non-steady swimming (i.e., burst-and-coast swimming) increased when feeding was stopped at high temperatures.Conclusion: Data storage tags that record multiple parameters are an effective tool to understand how cage-site conditions and management influence salmon (fish) behavior, physiology, and welfare in culture, and can even be used to provide fine-scale mapping of environmental conditions. The data collected here, and that in recent publications, strongly suggest that pathogen (biotic) challenges in combination with high temperatures, not high temperatures + moderate hypoxia (~70% air saturation) by themselves, are the biggest climate-related challenge facing the salmon aquaculture industry outside of Tasmania.
Highlights
The marine environment is becoming warmer, and experiencing more frequent and severe heat waves and hypoxic episodes as a result of climate change (Breitburg et al, 2018; Frölicher et al, 2018; Oliver et al, 2018; Holbrook et al, 2019; IPCC, 2019; Sampaio et al, 2021)
This study clearly shows the usefulness of data storage tags (DSTs) that provide information on several parameters simultaneously for studying aspects of salmon biology and welfare in culture
Star-Oddi: has recently increased the maximum recording length for ECGs to 18 s; is producing tags with the capability to record acceleration at 10 vs. 1 Hz [which will allow for the monitoring of a wider array of fish behaviors (Brown et al, 2013)]; and has developed a method to correct for changes in acceleration values if the tag shifts/rotates during long-term studies
Summary
The marine environment is becoming warmer, and experiencing more frequent and severe heat waves and hypoxic episodes as a result of climate change (Breitburg et al, 2018; Frölicher et al, 2018; Oliver et al, 2018; Holbrook et al, 2019; IPCC, 2019; Sampaio et al, 2021). To date, no studies have combined these technologies to examine how summer cage-site conditions affect the depth distribution, behavior/activity, and heart rate of Atlantic salmon; the predominant finfish species reared in North America, Europe, Chile, and Tasmania, and whose annual global production was ∼2.6 million tons in 2019 (worth ∼ US $12.5 billion) (Food Agriculture Association of the United Nations, 2020). To do this, the industry must better understand how sea-cage conditions influence the physiology and behavior of the fish
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