Narwhal teeth tell a disturbing story

Researchers have long debated what the 10-foot-long tooth is that actually erupts from the head of a narwhal for. Maybe it has something to do with sexual selection, and males with longer horns attract more females. Or maybe things feel salty. Or maybe a narwhal uses its fangs to flush out prey on the seabed.

Whatever the purpose, scientists know this for sure: the Arctic region, which the narwhales call, is warming twice as fast as the rest of the planet, and by analyzing these fangs, researchers can gain surprisingly detailed insights into how the animals interact. with catastrophic change. It does not look good.

In March, scientists wrote in the journal Current Biology, describing what they found in ten canines collected from animals in northwestern Greenland. Because a tusk grows continuously during the decades of a narwhal’s life, the researchers were able to read the teeth like the rings of a tree. They found that mercury in canines increased by an average of 0.3 percent per year between 1962 and 2000, but between 2000 and 2010 it increased by 1.9 percent per year. This is in line with increased mercury found in the bodies of other top predators in various regions across the North Pole, possibly due to air pollution blowing in from the south.

The scientists also find evidence in the teeth that the diet of the narwhal changes, from consuming species associated with sea ice to eating more open-ocean species. This is in line with a dramatic decline in Arctic sea ice since 1990.

“Instead of doing 40 years of work to gather 40 years of data, you can get narwhal teeth in one year and go back 50 years in time,” says Jean-Pierre Desforges, one of the paper’s lead authors. “So this is the most remarkable thing.”

Mercury is a powerful neurotoxin that bio-accumulates in species as they ingest it over a lifetime. When an organism consumes mercury at the bottom of the food chain, it accumulates in its tissues. Then eat something bigger that animal and its mercury, and so on in the food chain.

Some predators, such as the polar bear, accumulate a lot of mercury, but can also repel it – the bears bind it in their thick fur. No luck for the smooth skin narwhal. “For an animal that lives long – these whales can live more than 50 years – they accumulate mercury year after year,” says Desforges. ‘That’s why they’re coming to very high levels, and that’s why we’re worried. If these levels become high enough, it can negatively affect the species. This may include reproductive or cognitive effects, as mercury is a neurotoxin.

The other worrying signal that the researchers found in the fangs indicates the whales’ changing food sources. They searched for stable isotopes of carbon and nitrogen, residues of narwhal’s diet that linger in their fangs. Carbon reveals information about the prey’s habitat, for example if it lived in the open ocean or closer to land. Nitrogen tells you the trophic level of it, or where it was in the food chain. “Together, they give you an idea of ​​the overall nutritional ecology of the species,” says Desforges.

As with mercury, Desforges was able to map out how this diet changed over time. Before 1990, the whales fed a ‘sympathetic’ prey associated with icy habitat – North Pole cod and halibut. Then their diet began to shift to more ‘pelagic’, or open ocean, prey such as capelin, a member of the smelting family. “We’re not looking at the actual stomach contents of prey or anything,” Desforges says. “But we are essentially arguing that this temporary pattern agrees very well with what we know about the extent of the ice in the Arctic, which began to decline quite dramatically after 1990.”

A few things may be going on. As sea ice in the North Pole recedes, the ecosystems beneath it can rebound, leading to a decline in cod and halibut populations. In that case, the narwhalms will have to work hard to hunt for open ocean species to make up for their dietary shortages. On the other hand, the cod and halibut populations do not necessarily decrease, but just move north. Or it could be that there are more capelin in the North Pole water, and that the narwhal fish are not about to give up an abundant meal.

But if a fish is a fish, then why should it matter what the narwalms eat, as long as they get enough food? It seems that not all fish are equal. “Arctic species are more nutritious, energetic,” says Desforges. To survive the cold, fish need to pack fat, which means more calories for the predators that feed on it, such as narwhal fish. “If they move prey to less Arctic species, it could affect their energy intake,” adds Desforges. “Whether this is true remains to be seen, but it is certainly the big question we need to ask themselves.”

This dietary fluctuation – which is a problem for the narwhal or not – can clash with the rising mercury levels, which is a problem for any animal. These two threats can appear to be more problematic than alone. “That’s the tricky part,” says Desforges. “We actually have data that suggests things are changing, but we really do not know how it affects the whales here.”

The power of this technique-analysis technique is that it could theoretically allow scientists to look even further back in time than the 1960s. Taking a tissue sample from a living narwhal only gives you information about how the individual is doing at that moment. Natural history museums around the world have narwhal teeth in their collections that existed more than 100 years ago.

“Museum collections offer a wonderful opportunity to look at these changes even further,” says Moe Flannery, senior collection manager for birds and mammals at the California Academy of Sciences, who was not involved in this work. ‘Museum samples contain this hidden information that is not easily accessible, but is is accessible to researchers studying changes over time. ”

Look forward over time, however, it is difficult to say what a rapidly changing Arctic area will provide for the narwhal, and what signals of climate change we may find in the fangs in the future.

This story originally appeared on wired.com.