In recent years, mackerel have appeared in Greenland waters, and in their wake new and economically important fisheries have emerged. The first mackerel were caught in Greenland in 2011. And already three years later, in 2014, mackerel fishing had grown to make up entire 23 percent of the Greenlandic export earnings which is 78,000 tons of mackerel.
"The mackerel's arrival in Greenland is the most extreme example of how climate change can impact the economy of an entire nation," says Senior Researcher Teunis Jansen, DTU Aqua and the Greenland Institute of Natural Resources. Together with colleagues from DTU Aqua and the Greenland Institute of Natural Resources, Teunis Jansen is behind the first study of the mackerel's arrival and spread in Greenland waters. The results have just been published in the recognized journal Ecological applications. "We have mapped the occurrence of mackerel in Greenland's economic zone on the east coast from the Denmark Strait and to the south to Cape Farewell. And we more or less found mackerel everywhere in mid-summer. We found the largest quantities in warmer waters at a temperature of more than 8.5 degrees Celsius," says Teunis Jansen. And it is precisely the warm surface water which is an important key to understanding the mackerel's distribution in Greenlandic waters, assesses Teunis Jansen, based on the knowledge gathered. For in the same period, record-high temperatures have been measured in the ocean currents from the mackerel's spawning grounds west of the British Isles and toward the north-east of Iceland and Greenland.
When mackerel have spawned in the spring, they normally follow the Norwegian Current toward the north-east where they feed during the summer. But from around 2007, large quantities of mackerel suddenly appeared around Iceland in the Irminger Current -- the north-western branch of the Gulf Stream. Year by year they extended their migrations in this new direction, and in 2011 they were caught in Greenland for the first time. "One explanation for this is that where they used to turn right to follow the Norwegian Current, they have also kept left and followed the Irminger Current to the north-west. In recent years, record-high temperatures have been measured in the Irminger Current, and thus the mackerel have been able to use it as a 'motorway' while the population has grown and food availability has decreased in the east, so it has been attractive for them to find new feeding grounds," explains Teunis Jansen, DTU Aqua. Whether a few mackerel have been in Greenland in periods before 2011 is uncertain because these East Greenland regions are deserted without much summer fishing.
"Our results suggest that the local conditions have been acceptable for short periods of time, but compared to the present situation and the expected future scenarios, it has been insignificant. The areas with temperatures that are suitable for mackerel have doubled in the Greenlandic zone in recent years, and our forecasts indicate that they will expand and stretch for longer periods," assesses Teunis Jansen. However, he stresses that the catches in the fishing industry in 2015 were, in fact, less than in 2014 when the study was carried out. "Perhaps because the spring of 2015 was a little colder and because there were plenty of plankton to eat around Iceland many mackerel did not need to seek further to the east to become full -- so there is some variation from year to year. We are currently studying this variation, and in a few years, we may be able to provide fishermen with mackerel forecast a couple of months in advance."
For the Greenlandic economy, the mackerel have been a welcome visitor at a time when the traditionally important shrimp fishing has been declining due to a diminishing population. Other species have followed in the wake of the mackerel, e.g. the Bluefin Tuna which have been caught as bycatch in the mackerel fishery. The mackerel's arrival could, however, become a problem for some of the current species when the mackerel eat their food, and higher temperatures can make life hard for cold water species. "Climate change is a huge challenge and even if there will be more of these kinds of local positive stories, it is important that we do not use them as an excuse not to implement structural and technological changes. Globally, the disadvantages of climate change are still totally dominant," emphasizes Teunis Jansen, DTU Aqua.
Source: Technical University of Denmark