Fish welfare in offshore salmon aquaculture

Malthe Hvas,Ole Folkedal,Frode Oppedal

doi:10.1111/raq.12501

Abstract

AbstractTo accommodate further growth in the Atlantic salmon aquaculture industry, new production sites may well be established at more exposed locations along the coast or even offshore. Here, fish will encounter strong currents and powerful waves, which are avoided at traditional sheltered locations. Exposed locations offer several advantages and necessitate new technological advancements. However, the most crucial question is whether Atlantic salmon are able to thrive in these more extreme environments. In this review, we describe how strong water currents affect the physiology, behaviour and ultimately the welfare of the fish. If ambient current speeds exceed swimming capacities, fish become fatigued and get stuck on the cage wall leading to unacceptable welfare. The swimming capacity will depend on both the magnitude and duration of the current speeds encountered. Moreover, several environmental and biological factors modulate swimming capabilities, where temperature, body size and health status are particularly important to consider. A series of empirical studies are subsequently used to formulate welfare guidelines with regard to biological limits in exposed aquaculture. In addition, owing to the growing popularity of cleaner fish in salmon aquaculture, we also evaluate their usefulness at exposed sites. Overall, Atlantic salmon is a powerful sustained swimmer, and based on available site surveys of ocean currents, we conclude that the prospects for responsible farming at exposed sites looks promising. However, cleaner fish species such as lumpfish and ballan wrasse are poor swimmers and are therefore not recommended for deployment at exposed sites.

Highlights

In the latter half of the twentieth century, global aquaculture production increased dramatically from >1 million tonnes in 1950 to 16 million tonnes in 1990 and 80 million tonnes in 2017 (FAO 2011; FAO, 2019a)
Atlantic salmon is an athletic species with high sustained swimming capabilities, and as a eurythermal and euryhaline fish, it displays an impressive flexibility to cope well in different environmental conditions
Based on a series of empirical studies on swimming performance in growing post-smolts in combination with site surveys of ocean currents, we believe that responsible Atlantic salmon farming that ensures acceptable welfare is possible at more exposed locations

Summary

Introduction

In the latter half of the twentieth century, global aquaculture production increased dramatically from >1 million tonnes in 1950 to 16 million tonnes in 1990 and 80 million tonnes in 2017 (FAO 2011; FAO, 2019a). Global fisheries capture stagnated in the late 1980s owing to overexploitation of wild stocks and has stayed at a similar level since. Since commercial fisheries are exploiting wild stocks to and beyond their limit, while the human population is growing more rapidly than ever, aquaculture and the continuous development towards sustainable practices will only become more important in the future. The commercial fishery of this species is almost non-existent owing to historic overfishing and extensive habitat damage (Heen et al 1993; Knapp et al 2007). On-growing Atlantic salmon are farmed in sea cages along the coast in Northern Europe, North America, Chile and Tasmania. Global harvest has steadily increased from 0.2 million tonnes in 1990 and remained above 2 million tonnes since 2012 (FAO, 2019b)

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