Narwhals (Monodon monoceros) are iconic Arctic marine mammals that show seasonal migrations in response to the presence of ice. They spend their summers in ice-free coastal waters around Arctic Greenland, Canada and Russia, and move to deeper waters that are 95 percent covered in ice for the winter. They need to time their fall migration to coincide with the formation of ice floes so that they do not become stuck in the fast ice. As the climate has changed, ice has formed later each year and melted earlier in the spring, and researchers have wondered what impacts these environmental changes are having on narwhal seasonal movements.
The small whales, also known as ‘unicorns of the sea,’ are creatures of habit, following relatively inflexible migratory paths and patterns each year. And, since they are long-lived – most survive until they are at least 50, and some until they are 100 – it has always been thought that they would be more susceptible to the impacts of climate change. Animal species with long lifespans produce offspring relatively slowly and take longer to manifest genetic change or evolution than animals with shorter lifespans.
In a new study, published in the Proceedings of the National Academy of Sciences, researchers from universities in Canada and Denmark have used satellite telemetry to track the seasonal movements of 40 narwhals between 1997 and 2018. They have focused particularly on the timing of the animals’ movements and compared them with data on local and regional changes in temperature and ice formation.
The results of the long-term study show that, over the 21 years, narwhals have delayed the timing of their fall departure by around 10 days per decade. They leave their summer grounds later and later each year, and also take an average of about four days extra in the earliest phase of their transit. Currently, the pod of narwhals leaves its summer grounds 17 days later than it did in 1997.
“We looked at satellite tracking data spanning 21 years from the Canadian Arctic, and found significant delays in the timing of narwhal autumn migrations, where narwhals were remaining longer in their summer areas at a rate of 10 days per decade,” said Dr. Courtney Shuert, lead author and post-doctoral fellow in the Statistical Ecology Research Group in the University of British Columbia’s Institute for the Oceans and Fisheries (IOF). “There were also sex-specific differences in departures, with the male narwhals starting the migration out of the summering areas, while females, potentially with dependent young, departed later by almost a week.”
Narwhals have a preference for cold water, and their space use is largely tempered by ice cover and the availability of open water regions. As a result, they may be residing in coastal waters within the larger summering areas, until ice formation in the autumn, and an increasing risk of entrapment, forces them to move off to deeper waters in the wintering areas in central Baffin Bay. Other research has shown that ocean freeze-over in this area is shifting to occur, on average, around five days later per decade, thus matching the pattern of narwhal movement changes.
“There’s this general trend [towards delaying migration], but there’s also a lot of inter-annual flexibility, which highlights that they’re having this strategic approach to when they’re leaving and they’re tracking these broad-scale climate trends,” Shuert said.
These findings raise hope that narwhals in particular, and long-lived species in general, may be able to survive global warming despite their slower genetic evolution. Changing behavior patterns may be one of the only adaptive strategies available for species that exhibit high site fidelity and strong ties with migration routes, and that are faced with climate change.
Prior research has shown that many land animals and birds have been able to alter their migration patterns as the planet has grown warmer. But, as the researchers involved in the current study note, little research has been done to find out if marine species are doing the same. “The rate of change that we’re seeing now in the Arctic is a huge concern for a lot of animals because it could exceed how quickly the animals can adapt through evolution,” said Shuert. “But [these findings] really show this idea of behavioral flexibility and how important it can be to bolster these populations against change.”
Does this change in behavior mean that narwhals will be able to adapt to climate change successfully? “Unfortunately, departing later is not necessarily good news for the narwhal,” said Dr. Marie Auger-Méthé, senior author and an associate professor in the IOF. “Because staying in the summering grounds could result in further exposure to shipping traffic associated with the new iron mine, it may not be beneficial to the narwhals in the long term. We know they are sensitive to shipping disturbance, and that their stress levels have been rising over the past 20 years.”
“In addition, staying in their summering grounds longer could increase the chance of narwhals being caught in quickly freezing ice. Such ice entrapments can kill hundreds of narwhals.” The narwhals may also increase their exposure to predators, such as Orcas, by staying back in summering grounds or leaving the wintering grounds too early.
Climate change and loss of sea ice is creating stressors for these animals, and they are adapting to a new life in the Arctic. “Natural resource exploitation, ice breaking, and tourism are also impacting narwhal migratory patterns, “Auger-Méthé said. “Climate change and increased human exposure are creating additional stress for these whales, and with it, comes consequences for human activity as well.”
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