Climate change will affect the future of cod in Norwegian waters, including a reduction in the importance of the traditional spawning grounds off the Lofoten and Vesterålen areas.
A study by the Norwegian Institute of Marine Research suggests that cod spawning grounds could shift from Lofoten to the far northern coasts of Norway and Russia, and spawning grounds to the south off the Møre coast are already less productive than in the past.
‘The main explanation is warmer seas,’ said researcher and the Climate change and new potential spawning sites for Northeast Arctic cod report’s lead author Anne Britt Sandø.
‘It is known that cod change spawning grounds – not from year to year, but over a longer period. Periods with warmer seas mean a more northerly spawning, and when it gets colder, the cod spawn further south again.’
Scientists have yet to figure out exactly why this is, but cod have a list of requirement for the perfect spawning area, including the right temperature, depth and bottom conditions. Salinity can also play a role, but this is probably not as important as the other physical factors. In addition, there will be a number of biological conditions that influence cod’s choice of spawning area.
Anne Britt Sandø and colleagues from the Institute of Marine Research have looked at how physical factors influence spawning patterns. They have used a model to calculate the location of suitable spawning areas both back in time, which they can be verified against historical data, and into the future with expected climate changes.
Looking back, the researchers started from hot and cold periods. During the cold period (1965-1970), the Møre coast had large quantities of the ‘perfect’ water masses that the spawning cod prefer. The model’s figures accurately matched actual conditions. During thase years, a significant part of the spawning took place off Møre.
‘Then we did the same exercise for the future – to find out where the most suitable bodies of water would be up to 2070,’ Anne Britt Sandø explained, commenting that it was a surprise when the model showed the spawning areas off Møre and Lofoten disappeared completely. The ‘new’ spawning areas were off Finnmark and Murmansk.
Re-running the model without emphasis on salt content, spawning grounds in Lofoten appeared to be more promising, but all the same, the researchers recorded significant changes in the spawning areas.
‘We feel pretty confident that in 50 years, it will be a very realistic scenario that there will be more cod off Murmansk,’ Anne Britt Sandø said.
‘We cannot say for sure what is happening. Spawning is one thing, but the spawn must also have enough and the right food at the right time. In addition, it also has to hit the right ocean currents so that they move on to the growing areas in the Barents Sea. All this may not be the case with a new spawning area.’
The study also indicates that there may be other reasons why cod spawning habits change as temperatures vary. The spawning migration is probably also affected by the location of the ice edge is. The cod graze throughout the ice-free part of the Barents Sea. When the ice edge moves north during warmer periods, the distance to the southernmost spawning areas tends to increase. A large part of the cod simply does not extend as far south during the spawning migration.
‘Predicting spawning grounds using models is a simplification of reality. It is limited how much a physical model can tell us about upcoming spawning, but this is also the method we now have to shed light on future developments,’ Anne Britt Sandø said.
