As a result of climate change the Atlantic cod has moved so far north that its juveniles now even can be found in large numbers in the fjords of Spitsbergen. In summer 2013 biologists of the Alfred Wegener Institute therefore ventured to this specific region of the Arctic Ocean, which used to be dominated by the Polar cod. Here the scientists wanted to investigate whether the two cod species compete with each other and which species can adapt more easily to the altered habitats in the Arctic. An expedition report.
Early morning on the 16th of August 2013 the German research vessel Heincke leaves the port of Bremerhaven. On board are a handful of fish nets, two dozens empty aquariums and seven scientists on a mission: to fill the vacant fish tanks with hundreds of juvenile Atlantic and Polar cod. For this purpose they head north, pass by the port of Tromsø in Norway, and continue further to their destination: Spitsbergen.
Here they want to investigate the distribution of the two fish species. And they already have a suspicion: Due to warming water temperatures the Atlantic cod ventures farther and farther north and is now settling in the Arctic waters of the archipelago – where it encounters the region’s key species, the Polar cod. In case it comes to a rivalry between the species, the scientists assume that the highly adaptable Atlantic cod might hold the ground.
The scientists are, however, venturing to Svalbard for a further reason: They want to bring back Atlantic cod and Polar cod alive to Bremerhaven in order to investigate how these fish react to ocean acidification. Because human induced emissions do not only heat up the atmosphere. Carbon dioxide also diffuses into the oceans and slowly makes them more acidic. And the Arctic presents the perfect research conditions. As cold waters absorb more carbon dioxide, the high latitudes will be the first ones affected by the so-called ocean acidification.
Due to this research quest six scientists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research and a PhD student from the Heinrich Heine University of Düsseldorf now find themselves at a latitude of 80,5 °N 21°E. At this northern most point of their expedition a mere thousand kilometres divide them from the North Pole. From here they enter the cliffy fjord system of Spitsbergen and prepare themselves for their first haul. The crew attaches the net and fills buckets with water. The scientists gear up in their working clothes, bright and orange. Meanwhile expedition leader Dr Felix Mark watches the echo sounder: the pattern on the screen indicates they passed a shoal of juvenile fish in surface waters. Four degrees Celsius, too warm for Polar cod, he suspects.
The crew casts the fish lift, a device developed by Norwegian colleagues to carefully bring fish to the surface without harming them. The excitement on deck grows. They haul for twenty minutes, before the net is retrieved. Crewmembers and scientists grab the metal container of the fish lift and empty it into a basin on deck. The container is teeming with small Atlantic cods, haddocks, herrings, halibut larvae and dealfish. And polar cod? A total of two. The scientists transfer over 250 Atlantic cods and the two Polar cods into the aquariums.
The Heincke expedition to the Arctic in August and September 2013 was part of a national research project on Ocean Acidification, BIOACID. The programme includes scientists from 14 German research institutes, who investigate how declining pH levels affect marine ecosystems. Dr Felix Mark leads the so-called fish consortium within this programme.
A similar sight awaits the team the following day, as the RV Heincke sails into the Hinlopenstretet: plenty of Atlantic cod, yet no sight of its Arctic conspecific. They move on, heading southeast, where the cold waters of the Barents Sea push into the strait. Here the water temperature drops to 1,1 degree Celsius. However, the echo sounding does not detect any activities in the surrounding water.
Defeat is not tolerated and so they steam off to other fishing grounds. They advance towards the ice edge within the range of vision, no further, as the ship does not have any ice class. Here the echo sounding finally sends a signal. At a level below 140 metres they can identify fish swarms. And yet, as they haul the fish lift on deck, it barely holds any fish, let alone Polar cod.
Dismal prospects for the Polar cod, that once dominated the waters of Svalbard. While the scientists put more and more Atlantic cod into the aquariums, the two Polar cods from the first haul still are waiting for company. Not till the final days of the expedition, as they reach the Hornsund at the western side of Spitsbergen’s southernmost tip, they finally succeed. Jackpot! The buckets on deck are filled with juvenile Polar cod in all sizes and the scientists begin to select the biggest ones. The smaller fish they put pack into the sea, once they have recovered from the haul.
Felix Mark is satisfied: RV Heincke returns with fish tanks filled with Atlantic and Polar cod. A crucial success, because once back at the Alfred Wegener Institute in Bremerhaven he and his colleagues will need these fish for their experiments on how the two species react to ocean acidification. Experiments that will span over the following year.
(Kristina Bär)
"We are talking about a deadly trio"
The evil little brother of
global warming
A view inside –
A fish in the NMR
Dr Felix C. Mark
