By Leya Musa
Polar bears are well-known to store many deadly pollutants in their fat. They store chemicals such as PCB’s from the food that they eat. Being at the top of the food chain leads them to have high concentrations of toxins. New research indicates that polar bears are no longer some of the most polluted species in the Arctic. The Greenland shark is even more contaminated.
While PCB contamination of the ecosystem in the Arctic is beginning to ease following the banning of the chemical 30 years ago new pollutants – especially those used in fire-retardants – are becoming more widespread in the region. The new pollutants are also accumulated throughout the food chain and can be particularly damaging to wildlife as they can interfere with hormone production. Some polar bears in the Arctic are already recorded to be hermaphrodites – with both male and female sex organs – because of the action of the chemicals.
A study by a team of marine researchers from Norwegian University of Science and Technology (NTNU), the Norwegian Polar Institute and Windsor University in Canada have shown that the fat in the Greenland shark can contain more of these toxins that the fat of polar bears.
The researchers wanted to study behaviour, distribution, population size, concentrations of pollutants and the effect of pollutants on the species. Forty-three individuals were marked with a tracking device and a depth gauge. The researchers also took liver samples.
This species has not been extensively studied before, and for a long time researchers thought that the Greenland shark was a carrion feeder. But the shark catches a lot of live prey, both fish and seals. The liver samples showed accumulation of alarmingly high concentrations of PCB, brominated flame retardants and other pollutants.
“We think this is due to their diet, because Greenland sharks around Svalbard eat a lot of seals, which are high on the food chain, which leads to an accumulation of pollutants,” explained Professor Bjørn Munro Jenssen, an NTNU biologist who specialized in pollutants and arctic biology.
The researchers were surprised to find such high levels of contaminants in the sharks. Previous studies of Greenland sharks around Iceland, Greenland and in the waters off Canada have shown much lower contaminant levels. This is due to differences in diet, the researchers say.
“The reason we found lower concentrations (in these areas) is because the sharks eat less seal. Around Svalbard, 43 per cent of the individuals we studies had seal remains in their stomachs. In Canada, around Iceland and off Greenland, we found seal in only 14 per cent of sharks. There the sharks prey lower down in the food chain, mostly on fish, which again results in less accumulation of pollutants,” Jenssen said.
Because the Greenland shark can live up to 100 years in the wild and are very poor at excreting toxins it means that concentrations of pollutants in the body can build up over time to very high levels.
“We can conclude that the contaminants lead to reduced levels of vitamin A and increased levels of vitamin E in the sharks around Svalbard, but we don’t know if this affects their health or reproduction. We would have to study the species for many years,” says Jenssen.
“It seems that animals mobilize vitamin E stored in the liver and send it into the blood stream. Greenland sharks seem to be able to do this when needed. Lower levels of vitamin A in the body lead to a reduced immune defence and may affect reproduction negatively,” he added.
Because the contamination of sharks – and polar bears – is related to the food that they eat the researchers warn that there may be even more contaminated sharks than the ones found at Svalbard.
“If we had polar bears along the Norwegian coast or measured pollutants in Greenland sharks along the shores or in the fjords you would make surprising finds,” Jenssen says. “You could expect far higher concentrations. Seals living along the coast in Trøndelag in mid-Norway have pollutant levels five times higher than those in seals around Svalbard. In the Oslo fjord the levels are ten times higher.”