Sea water temperatures are on the rise, particularly affecting the North Atlantic, which underwent several "extreme" and "beyond extreme" marine heatwaves this year, as defined by the US National Oceanic and Atmospheric Agency (NOAA).
The waters around Norway are no exception, with some parts of the country experiencing summer sea temperatures well above normal.
It has already been established that extended periods of elevated water temperatures are bad news for fish, provoking disease, toxic algal blooms and even mass die-offs. But what are the specific risks to Norwegian aquaculture in the years to come?
Nofima Senior Scientist Dr Elisabeth Ytteborg is studying just that, connecting longer-term climate projections with consequences for fish health, in the hopes that her research can provide practical knowledge to aid Norwegian fish farmers.
“We look at the climate crisis under a microscope, because the details are important when implementing fish farming measures while temperatures are rising,” says Ytteborg, in a press statement on the research project.
Ytteborg's research scales down UN climate projections to the level of individual farming sites in Norway. Currently, she is focusing on farmed cod, and has found that the seawater temperatures expected in some Norwegian farming sites by 2030 are well above cod's normal temperature range - and what's more, can significantly damage fish skin.
In the research, Ytteborg and her team chose a cod farming facility located at Dønna, Nordland county in the north of Norway, that also has good data on cod farming and the environment.
The scientists wanted to study the impact of temperature on fish health, and compare this to the effects of cod when infected with the Fransicella bacterium.
Cod prefer temperatures between 8 and 13 degrees celsius. However, by 2030, the facility at Dønna may experience days above 17°C. The research team therefore studied the effect temperature had on cod skin between 12 and 17°C.
"The results showed that temperature has much more of an effect on barrier tissue functionality compared to infection with Fransicella bacteria," Nofima said in a press statement.
"At high temperatures, cod suffered damage between cells that bind the skin together. These skin bonds seem to affect the fish’s ability to heal wounds, and damage to them can make the fish more susceptible to other stresses."
"In other words, the cod’s barrier system is weaker if it faces a challenge in addition to increased temperature."
Ytteborg says there are currently several cod farms further south in Norway which can expect higher sea temperatures - which makes it essential to take climate change into account when planning future fish farming development in the country.
“The impact of high temperatures and how to deal with them will play a more important role in the future in line with climate change. How much the fish can tolerate will be important in finding good measures to safeguard fish health if the water becomes too hot,” says Ytteborg.
“We are releasing a publication on diversification where we look at 36 different species and their temperature tolerance in relation to climate change. If Norway is going to have a longer-term diversification plan, one should definitely focus on temperature," she adds.
The research is financed by Troms and Finnmark county authorities in Norway.
