Sea Warming
A long term threat to salmon farming?
Two key reports are pointing to sea warming as a potential long term threat to Atlantic salmon farming. They come from slightly differ ent sources, but the message on rising temperatures seems to be the same. The first report is from the Norwegian University of Life Sciences (NMBU), while the other was published earlier this year by EU MOFA, the European Market Observatory for Fisheries and Aquaculture.
First, the NMBU analysis which says that while the seas off the Norwegian coast are currently ideal for salmon, but they are starting to warm up and it is sending out signals that problems lie ahead.
Øystein Evensen, professor of aquaculture at the NMBU Veterinary College, said temperatures should range from eight to fourteen degrees Centigrade, with the ideal level being 13 degrees Celsius.
But if the waters warm (as a significant group of marine biologists says is now happening) then the salmon become stressed, they eat less and grow more slowly.
He said Atlantic salmon were, by nature, car nivores, with a great need for oxygen to grow and thrive. In warmer seas the supply of oxygen decreases and with sustained temperatures of 20 degrees Celsi us, normal body functions break down and the fish suffocate. And very low sea temperatures have the same effect.
The report also says research from the University of Tasma nia in Australia clearly showed stress related damage to the liver when salmon were exposed to high
temperatures over time (21 Degrees Celsius for example
Farmed salmon do not have the opportunity to escape or swim away when the water temperature rises. Salmon’s solution is to swim down the cage. The deeper, the colder the water gets, and the more oxygen it contains. The fish will naturally swim downwards and it gets crowded, says Professor Evensen.
And, as a fish farm is usually no more than 40 metres deep, the temperature rises on or near the surface and the fish will swim down into tighter spaces which can lead to stress and eventually death.
This happened at a farm owned by Northern Harvest Sea Farms off the coast of Canada last autumn when 2.6 million fish died over a 13 day period.
Recent research by Nofima and the EU funded project Climefish says that climate change will see sea temperatures continuing to rise with all that means for the salmon.
The worry is that changes may take much faster than biology can adapt. In southern Norway where temperatures could be high for most of the year there may be problems with fish in cages.
Rising temperatures also lead to increased instances of salmon lice, one of the main challenges facing aquaculture companies.
While this is all bad news for the industry there are various methods that can help salmon withstand warmer waters, says Øystein Evensen.
He suggests targeted breeding as one longterm way of improving animal welfare for the fish and limiting losses for the industry.
Another solution could be to add oxygen to the cage using the latest technology. For example, an air blower could provide higher oxygen levels particularly in the upper water layers.
‘It is very important for the animal welfare of the salmon, and Norway’s salmon farming, that we take climate change seriously,’ Evensen stresses.
The EUMOFA report also touches on how Climefish has been tackling the issue to help aquaculture operators and fish producers predict, prepare and adapt to climate change. It says:
‘Partially supported by ClimeFish, a team of researchers found that since the 1980s, ocean temperatures off the Norwegian coast have risen by 1 °C on average.
‘The researchers predict further increases over future decades as likely to create problems for salmon farming’.
The team has examined the impact of different temperature scenarios on salmon farming, covering all 13 production regions in Norway for each decade between 2010 and 2069. Quoted in the same news item, Nofima scientist Dr. Elisabeth Ytteborg says:
‘Even under the mildest scenario we see that rising ocean temperatures may pose a challenge for salmon’.
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If the waters warm the salmon become stressed, eat less and grow slowly” more
Dr. Ytteborg also believes new technologies, along with breeding for improved temperature tolerance and alternative farming locations are some of the solutions that could help maintain healthy fish:
‘When it comes to determining which measures we should implement, we still don’t know enough about how the farmed salmon will react to higher temperatures and increased ocean acidification.’
People may continue to debate the causes of climate change, but the two reports make it clear there is no doubt it is happening – and with consequences for the future of fish farming.