A disturbing story told by Narwhal Tusks
Researchers found another worrying sign in their teeth that whales warned about changing food sources. They looked for stable isotopes of carbon and nitrogen, the remnants of the narwhal diet that remain in their teeth. Carbon shows information about prey habitat, for example, if it lives in the open ocean or closer to the earth. Nitrogen tells you where its trophic level or food chain was. “Together, they give you an idea of the overall nutritional ecology of the species,” says Desforges.
As with mercury, Desforges could map out how this diet changed over time. Prior to 1990, whales fed on “sympathetic” prey associated with frozen habitat — artichoke cod and halibut. Then their diet began to shift to “pelagic” or “wider oceans” of prey like capelena, a member of the family scent. “We don’t look at the stomach prey or anything,” Desforges says. “But we’re basically arguing that this time pattern fits very well with what we know about the extent of Arctic sea ice, which has been falling quite significantly since the 1990s.”
A couple of things could happen. As the Arctic sea ice recedes, the underlying ecosystems may continue to rebuild, and the population between Arctic cod and halibut will decrease. In that case, narwhals would have to go hunting for species in the open ocean to make up for the diet deficit. On the other hand, these cod and halibut populations will not necessarily decline, but will move north. Or it could be that when the waters of the Arctic become warm, there will be more capelin and narwhals not going to spend a hearty meal.
But if a fish is a fish, why would it matter what narwhals eat, as long as they get enough food? It turns out that not all fish are created equal. “The Arctic is more nutritious, in terms of energy,” says Desforges. To cope with the cold, fish need to be packed with fat, which means more calories for predators that feed, like narwhals. “If prey is shifting to fewer Arctic species, this could have an impact on their energy intake,” Desforges added. “It remains to be seen whether that is true, but it is certainly a big question we need to start asking ourselves.”
This reshaping of the diet — whether or not it may be a problem for nature — could clash with a rise in mercury levels. are the problem for any animal. These two threats can be more problematic than just one. “That’s the hardest part,” Desforges says. “We basically have data that suggests things are changing, but we really have no idea here how whales can affect us.”