SALMONIDS

Climate change and potential effects on salmon farming

By Asbjørn Bergheim*

Increasing sea temperatures could affect performance under farming conditions: if the water is warmer than 16°C, salmon get stressed, eat less and their growth can be reduced. Atlantic salmon living at 19°C reduce their feed intake by 50% compared to salmon living at 14°C with the growth occurring at the same rate as observed for 3°C conditions. Salmon may die at temperatures above 23°C. When the temperature rises, dissolved oxygen con

The ideal water temperature for salmon appetite and growth is in the range of 8 - 14°C.

tent generally drops while the oxygen consumption of the fish increases. Additionally, algal blooms and salmon gill disease are considered more prevalent in warmer water.

Since the 1980s, the open sea temperature off the Norwegian coast has increased by 1 ˚C. The temperature will continue to rise due to humancaused climate changes. This is bad news for farmed Atlantic salmon, which will be vulnerable to these temperature changes. Nevertheless, Atlantic salmon have higher tolerance to warm water than Pacific salmon and some other species in the genus Salar such as Arctic charr and brown trout. Among other things, warm water can reduce fecundity and growth, and increase susceptibility to disease. “Salmon farming as an industry with high technological integration could react to mid- and long-term changes but may not be prepared to face sudden or temporary changes in parameters such as surface tempera-

When the temperature rises, dissolved oxygen content generally drops while the oxygen consumption of the fish increases. Additionally, algal blooms and salmon gill disease are considered more prevalent in warmer water.

ture, salinity or near-surface stratification. The latter, for example, may trigger harmful algal blooms or enhance hypoxia events that cause direct mortality or produce conditions that deteriorate performance and health in farmed fish” (Reviews in Aquaculture, 2019).

Stress-inducing and growth-depressing conditions can occur in late summer and autumn with high temperatures, low early morning oxygen levels and peak biomass in the salmon cages. Such conditions affecting salmon cages were observed during the warm summer/autumn of 2002 along the Norwegian coast, where many farms suffered high mortality and low growth. A similar situation occurred during the same period in Maine and along the coast of British Columbia.

Mowi Scotland recently reported increased mortality in 2019. Last

year’s sea temperatures were the second highest of the last decade and provided ideal conditions for harmful algal blooms in the third quarter of 2019 (Figure 1). The high mortality losses at several farm operations

Dr. Asbjørn Bergheim is a consultant at Oxyvision Ltd. in Stavanger. His fields of interest within aquaculture are primarily water quality vs. technology and management in tanks, cages and ponds, among others. asbjorn@oxyvision.com coincided with an algal bloom and increased sea lice levels. Significantly increased temperatures also represent a health and welfare challenge to the cleaner fish stocked with salmon, especially to the commonly-employed cold water lumpfish species.

As part of an EU-funded project (ClimeFish) performed by researchers at Nofima and the University of Stirling, the effects of climate model scenarios on salmon farming along the Norwegian coast over the next 50 years have been assessed. Climate adaption measures will in many cases be farm-specific, e.g. use of deeper nets or changes in stocking strategy. More advanced solutions will be required in other locations, such as transfer to semi-closed containment systems (S-CCS) supplied with deep water or the introduction of selective breeding programs to produce temperature tolerant strains.

The climate conditions along the Norwegian coast vary greatly across 13 degrees of latitude, from 58˚ to 71˚ north. At the southernmost farm locations, measurements of surface water show a large number of days with temperatures above 16 ˚C during summer – early autumn, and several days reaching above 20 ˚C. In the next decade, the projected surface water peaks in one location (according to ClimeFish) will occasionally approach 28 ˚C! Increasing temperatures in Mid-Norway are likely to affect production, however, the nearfuture extremes are not projected to be as high as at the southwestern coast site.

Increased temperatures at northern sites will reduce the number of days with readings below 4 ˚C, especially in the 2030s and onwards. This may lead to improved growth in this region but it may also increase the prevalence of diseases and parasites (e.g. sea lice) more common at higher temperatures. The study report indicates the importance of considering the direct and indirect impacts of temperature change throughout the year. In a recent assessment of climate change vulnerability for the salmon farming sector in southern Chile, reduced precipitation, a change in salinity and increases of air and surface sea temperatures are the most foreseen climate change drivers, especially in Regions X and XI (Figure 2). The vulnerability matrix indicated that communities with higher salmon production concentrations were more exposed (INCAR, Chile). The models employed also allowed the researchers to explore the reduced vulnerability associated with a southward movement of the salmon production towards the Magallanes region. Significantly increased temperatures also represent a health and welfare challenge to the cleaner fish stocked with salmon, especially to the commonly-employed cold water lumpfish species.