In 1576, Queen Elizabeth I paid the equivalent of half a million dollars for a unicorn horn, which she believed could neutralize poison. Of course, it wasn’t a unicorn horn at all, but a narwhal tusk, remarkable in its own right.
Today, over 440 years later, narwhals continue to surprise and attract attention. A recent paper in Biology Letters by Kristin Laidre et al. examined narwhal visits to glacial fronts in West Greenland.
“We don’t fully understand the relation between narwhals and glaciers,” professor Mads Heide-Jørgensen of the Greenland Institute of Natural Resources told GlacierHub. Laidre added, “Narwhals in places like the Canadian Arctic, for example, have limited access to glacial habitat. However, in Greenland, most narwhals are close to glaciers in summer because Greenland is so glaciated, and there are glaciers along the entire coastline.”
It has long been observed that narwhals visit glacial fronts in the summer and autumn, but it is unknown why they seek out this habitat. “Glaciers are productive regions,” commented Laidre. “They attract prey, there’s upwelling and nutrient cycling, and sometimes even osmotic shock to small invertebrates which attracts fish… We hope future studies will help us understand this, but we don’t know exactly why they go there.” Belugas, the “sister species” to the narwhal, also favor freshwater habitat in the summer, seeking out shallow water estuaries.
To begin answering this question, Laidre took a novel approach, forming an international, cross-disciplinary team that included scientists from the U.S., Denmark, and the U.K. “The idea was to get biologists and glaciologists to collaborate and share data in an interdisciplinary way,” Laidre said.
The team evaluated which glacial characteristics draw narwhals by collecting data from 15 satellite-tagged whales and following their movements through the fjords of Melville Bay in West Greenland. The narwhals demonstrated three preferences: they spent more time at glaciers that discharge a fresher, rather than siltier melt; they preferred slower-flowing glaciers, which are more stable and calve less; and they favored thicker glacial fronts, perhaps because they maximize access to freshwater.
Sea ice also provides important habitat for narwhals. “All narwhal populations winter, and some even summer, in dense sea ice concentrations,” said Heide-Jørgensen. In summer, narwhals spend time in the high Arctic where ice has receded, and in fall, the ocean freezes solid, pushing the narwhals away from shore, Laidre explained. “They swim away from the forming ice and move offshore, where they overwinter in dense ice cover with cracks so they can breathe. Narwhals are highly associated with sea ice, perhaps the most of all whales,” he said.
Heide-Jørgensen indicated that narwhals will seek out the sea ice when it decreases in coverage rather than wintering in open water. “Reduction of sea ice therefore implies a reduction in habitat, and this will again introduce a reduction in prey base or carrying capacity. In short, less sea ice means less narwhal habitat and eventually less narwhals,” he said.
Laidre agreed that “changes in sea ice and the marine ecosystem will likely be the most important factor” to the future of narwhals as climate changes. Since 1979, sea ice freeze-up has occurred almost a month later in Baffin Bay and Melville Bay, where this study took place, and glaciers, of course, are retreating. But far from being simple victims of global warming, narwhals can aid in the collection of data that can help mitigate climate change.
In 2005 and 2007, Laidre took advantage of narwhals’ capacity for deep dives and tendency to winter in sea ice, outfitting narwhals with temperature and depth sensors. Narwhals regularly dive over 1,700 meters to hunt bottom-dwellers like Greenland halibut, and 90 percent of the recorded dives reached the bottom. This method effectively turned narwhals into self-powered oceanographic instruments and allowed the researchers to collect wintertime data in Baffin Bay, the dearth of which had long been felt in climate records.
Perhaps, most importantly, the study proved that narwhals can constitute an effective ocean observation platform in remote areas where dense ice cover prevents regular instrument deployment. In this way, narwhals are even more magical than the unicorn Queen Elizabeth I imagined.