With their shimmering silver bellies and iridescent blue backs, mackerel are striking fish. Sushi aficionados savour their clean, salty taste while superfood advocates prize their healthy omega-3 oils. For the tiny North Atlantic nation of Iceland, however, mackerel are a harbinger of ocean warming. Until about 2000, mackerel were a rare sight in Iceland, an island whose people have survived for centuries by fishing. But today they are one of the country's most commercially important fish, both in terms of value and volume. In 2016, mackerel was the third largest catch for Iceland and its third-most-valuable fish, bringing in $103 million or 8 percent of the nation's total catch value.
"This mackerel story is maybe one of the most marked ones... demonstrating the changes taking place in the fish stock in the North Atlantic in recent years," said Olafur S. Astborsson, a scientist at Reykjavik's Marine and Freshwater Research Institute (MFRI), which advises the Icelandic government on catch levels. Rising ocean temperatures have altered fish stocks around Iceland, with southern species migrating northwards and northern species shifting even further north, he told the Thomson Reuters Foundation. Iceland has also seen 31 new species of fish in its waters since 1996, including blue sharks, flounder, megrims and black devil anglerfish, Astborsson said. Their numbers are not large, but "they are signs of changing times", he added.
As climate change brings warmer temperatures in many parts of the world, a growing number of fish species are swimming into new waters, seeking out the temperatures they prefer and shifting fisheries along with them. Some of the biggest changes have come in Arctic marine ecosystems, which scientists say are warming twice as fast as the global average and creating dramatic changes in fish stocks. Countries in the far north, such as Iceland, are expected to reap the benefits of climate change, as valuable fish species turn up waters that were previously too cold. But some experts warn that the picture isn't clear cut. Warming waters could also bring new predators and diseases - and potentially new geopolitical tensions, they say.
The waters around Iceland have warmed between 1 to 2 degrees Celsius in the last 20 years, said Hreidar bor Valtysson, a professor at the Faculty of Natural Resource Sciences at the University of Akureyri. Valtysson's children can now catch mackerel - a fish usually associated with warmer climes - at the harbour in Akureyri, a town in northern Iceland just 60 km (37 miles) south of the Arctic Circle. Studies suggest climate change could aid shipping and tourism in northern economies, as well as fishing, but Valtysson remains unsure. Cold water species such as northern shrimp and capelin, which are important for Icelandic fisheries, are declining, he said. Climate change is also increasing the acidity of the world's oceans as the water absorbs some of the carbon dioxide building up in the atmosphere. That could have serious effects on sea life, including making it harder for shellfish to build strong shells, he said.
New diseases are also appearing and although it is still unclear how much of a factor rising temperatures played, Iceland's scallop stock has collapsed and there have been mass deaths of herring, Valtysson said.
"The gains and losses seem to be balanced for now. But in the longer-term, I think it will be slightly positive," he predicted. Fishing was once the largest industry in Iceland, but its share of GDP has been declining as the country's tourism and energy businesses boom. In 2007, Iceland was ranked 15th among world's largest fishing nations. By 2014, the country had dropped to 19th. Still, fisheries remain integral, said Ragnar Arnason, an economics professor at the University of Iceland. Nearly a tenth of Iceland's economy is directly related to fishing, and the figure rises to nearly 20 percent if associated industries are taken into account, Arnason said.
That means any change to the country's fishing industry could substantially affect its $16.7 billion economy, which has now recovered from the painful collapse of its financial industry in 2008.