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The ivory of a narwhal tells a disturbing story



The ivory of a narwhal tells a disturbing story

Science and Society Image Library | Getty Images

Researchers have long been debating what the 10-foot-long teeth erupting from the head of a narwhal are. in order to. Perhaps this is related to gender selection, and men with long horns will attract more women. Or maybe things will feel salinity. Maybe the narwhal will use its ivory to wash away the prey on the bottom of the sea.

Whatever the purpose, scientists will know this: the Arctic region, which narwhals call home, is heating up twice as fast as the rest of the earth, and by analyzing these tusks, researchers can surprisingly collect Detailed insights on how animals are handled.It̵

7;s not pretty

In March, scientists published an article in the journal Current Biology, describing what they found in 10 teeth collected from animals in northwest Greenland. Because ivory has been growing for decades in the life of narwhals, researchers can read teeth as large as tree rings. They found that between 1962 and 2000, mercury in teeth increased by an average of 0.3% per year, but between 2000 and 2010, it increased by 1.9% per year. This is related to the increase in mercury found in the bodies of other top predators in other regions of the Arctic, which may be due to air pollution blowing from the south.

Scientists have also found evidence on ivory that the narwhal’s diet is changing, from eating species related to sea ice to eating more open marine species. Since 1990, this has corresponded to a sharp decrease in Arctic sea ice.

Jean-Pierre Desforges, a wildlife toxicologist at McGill University, said: “You don’t have to spend 40 years of work to get 40 years of data, but you can get narwhal ivory in a year of work, and it can be traced back to 50 years. Years later.” Paper. “So that’s really an amazing thing.”

A cross section of the narwhal ivory showing the layers of material.
enlarge / Cross section of narwhal ivory showing material layers.

Jean Pierre Des Voges

Mercury is a potent neurotoxin that bioaccumulates in species when ingested during its lifetime. When organisms at the bottom of the food chain consume mercury, it accumulates in their tissues.Then something bigger ate that animal with Its mercury, etc. are in the food chain.

Some top predators, such as polar bears, accumulate large amounts of mercury, but also expel it-bears absorb it in thick fur. The smooth narwhal has no such luck. Desforges said: “For long-lived animals (these whales can survive more than 50 years), they accumulate mercury every year.” “That’s why they reach really high levels, and of course this is why we are concerned. If these levels are sufficient High, may have a negative impact on the species.” Since mercury is a neurotoxin, it may include reproductive or cognitive effects.

Another disturbing signal the researchers found in ivory hints at the changing food sources of whales. They look for stable isotopes of carbon and nitrogen, which are the food residues of narwhals remaining in their teeth. Carbon reveals information about the habitat of the prey, for example, whether it lives in the open ocean or is closer to land. Nitrogen tells you its nutritional level or position in the food chain. Desforges said: “Together, they provide you with the concept of the overall foraging ecology of this species.”

Like mercury, Desforges can map how this diet changes over time. Prior to 1990, whales had been preying on “symbolic” prey associated with icy habitats-Arctic cod and halibut. Then their diet began to shift to more “pelagic” or open ocean prey, such as Capellin, a member of the capelin family. Desforges said: “We are not looking at the actual stomach contents of prey or anything.” “But we are essentially arguing that this time pattern is very consistent with our understanding of the extent of the Arctic sea ice, which was after 1990. The range began to drop sharply.”

As the sea ice decreased, the narwhal changed its diet. At the same time, the mercury content is also rising.  ”Src =“ https://cdn.arstechnica.net/wp-content/uploads/2021/04/tracers-640x465.jpg” width = “640“ height =” 465 “srcset =” https://cdn.arstechnica .net/wp-content/uploads/2021/04/tracers-1280x930.jpg 2x
enlarge / As the sea ice decreased, the narwhal changed its diet. At the same time, the mercury content (Hg) has been rising.

Jean Pierre Desvoges

Several things may have happened. As the Arctic sea ice recedes, the ecosystem below it may be reorganizing, resulting in a decline in the population of Arctic cod and halibut. In this case, narwhals will have to resort to open marine species to make up for their dietary deficiencies. On the other hand, the number of cod and halibut is not necessarily decreasing, but only moving northward. Or, it may be due to the warming of Arctic waters, there are more capelin around, and the narwhal will not waste a lot of food.

But if a fish is a fish, then as long as they get enough food, why would narwhals eat? It turns out that not all fish are created equal. Desforges said: “Arctic species are more nutritionally valuable.” In order to survive in the cold, fish need to supplement fat, which means that like narwhals, predators who feed on them also need more calories. Desforges added: “If they move their prey to fewer Arctic species, it may affect their energy intake.” “Whether this holds true remains to be seen, but this is undoubtedly a big question we are starting to ask ourselves.”

This change in diet (which may or may not be a problem for narwhals) may conflict with rising mercury levels, leading to higher mercury levels. Yes It is a problem for any animal. The combination of these two threats may be more difficult than the separate problems. Desforges said: “This is the tricky part.” “We basically have data that shows that things are changing, but we really don’t know how this will affect the whales here.”

The powerful function of this ivory analysis technique is that, in theory, it can enable scientists to go back to the 1960s. Taking a tissue sample from a living narwhal will only provide you with data on how the individual behaved at the time. However, natural history museums around the world have narwhal ivory in their collections dating back 100 years.

Moe Flannery, senior collection manager for birds and mammals at the California Academy of Sciences, said: “The museum collection provides a great opportunity to study these changes in depth,” and he was not involved in the work. “Museum specimens hold this kind of hidden information that is not easy to obtain, but Yes Researchers who study changes over time can visit. “

Watching forward However, over time, it is difficult to say what a rapidly changing North Pole will bring to the narwhal, and the signs of climate change that we may find in its ivory in the future.

This story originally appeared on wired.com.


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