Behavior Biology Climate Change

Orca vs Narwhal

Paper: Breed, G., Matthews C., Marcoux, M., Higdon, J., LeBlanc, B., Petersen, S., Orr, J., Reinhart, N., Ferguson, S., (2017).  Sustained disruption of narwhal habitat use and behavior in the presence of Arctic killer whales.  Proceedings of the National Academy of Sciences.  114(10): 2628-2633. doi: 10.1073/pnas.1611707114


Orca image credit: Nicolás Ruiz de la Corte via Wikipedia commons, CC BY-SA. Narwhal image credit: Piotr Siedlecki via, CC0.


Why are you in a certain place at any given time throughout the day?  Many factors probably affect where you are, when and what you’re doing.  For example, one might find you in a kitchen or restaurant sitting down eating when you’re hungry, out on the town or swiping on your phone if you’re trying to find that special someone, and laying low to avoid your arch nemesis at all costs.  The same goes for narwhals (Monodon monoceros), better known as unicorns of the sea (their tusk is actually their left erupted, spiraled tooth that can reach 8 feet long!), a new study finds.  


Still from this excellent Marine Arctic Ecosystems Video:

Narwhals are part of the Arctic ecosystem.  Along with bearded seals, harbor seals and belugas, they are medium high in the food web, eating smaller animals such as squid, fish and shrimp, but also getting preyed on by larger animals such as orcas (Orcinus orcas) and being hunted by some Arctic indigenous peoples for subsistence.  In the past, thick summer sea ice acted as a gatekeeper, blocking off open water species such as orcas from going into certain areas such as Hudson Bay.  However, warming ocean waters due to a buildup of heat trapping gasses in our atmosphere from burning fossil fuels, is causing sea ice to decline.  This means, areas that were previously off limits are now opening.  And areas that orcas have accessed in the past will now be open earlier and longer, allowing more of them to move in.  


Greg Breed, a scientist at the University of Alaska, along with his team representing Fisheries and Oceans Canada, Assiniboine Park Zoo and University of Manitoba wanted to study if narwhals would change what space they occupied and/or their behaviour in response to more predator exposure.  So, they tagged and tracked a orca and seven narwhals off the northern most tip of Baffin Island in the Eastern Canadian Arctic in 2009 (see Figure 1).  In the summer, this area known as Admiralty Inlet supports around 35,000 narwhals or around ⅕ of the world’s population.  Behaviour data such as swim speed, swim direction, depth and distance from shore were then analyzed for the orca (which represented around 12-20 orcas that traveled together in a narwhal death posse) and for the seven narwhals until the orcas left the area–a span of 10 days.  

Figure 1: Coastal landscape of Baffin Island (Credit: tpsdave via pixabay, CC0) with map of Canada with Baffin Island indicated in red in left corner (Credit: Connormah via Wikipedia Commons, CC BY-SA)


After analyzing the data, it was clear that narwhals had two different types of movement:  transit (sharper turns and longer time spent traveling in one direction) and resident (see Figure 2).  In fact, the narwhals were so stressed, they pretty much stayed in a small area close to the shore and in shallower waters.  When the orcas left, the narwhals moved offshore and dove deeper.  

These results show that narwhals are stressed for the duration of the time orcas are in the vicinity.  Studies of habitat use by any given animal is usually limited to characteristics of the environment such as temperature and salinity as well as where their food is and where their mates are.  However, this clearly shows that predator presence is a strong deciding factor of where any animal goes, and this should be included in future studies.  


Figure 2: Horizontal strike through lines show narwhal behaviour during exposure to orcas (white background) and after exposure (grey background). Blue represents transit behaviour and red represents resident behaviour. Note the behaviour switch from transit and resident during orcas present contrasted with purely resident behaviour after orcas have left. For more information about the other coloured lines, please see Breed et al., 2017 paper linked above.


And in the end, how will increased exposure to orcas affect narwhals?  Well, narwhal health could become significantly affected which may impact their conservation status (they are currently categorized as Near Threatened under the IUCN).  For example, in the presence of predators, narwhals would spend less time foraging for food, socializing with other narwhals, and reproducing.  This will not be the only impact for a changing Arctic ecosystem that is warming faster than the rest of the world.  Less summer sea ice also will also impact species that depend on ice including some species of algae that make up the base of the Arctic food web, as well as species such as ringed seals, bearded seals and polar bears that need ice to forage and mate.  These changes affect people too!  Although the Arctic seems far away, there are many Arctic communities whose culture and survival rely on the functioning of the Arctic ecosystem–including a healthy population of narwhals–they are part of.  In addition, the fisheries of many Arctic nations such as the USA (Alaska), Canada, Denmark, Finland, Iceland, Norway, Sweden and Russia are getting harder to predict and manage as fishes, crabs and shrimp distribution shifts.  

There is a lot of uncertainty surrounding how our world will change in response to a changing climate.  However, science is helping untangle and predict the impacts of climate change such as sea level rise and extreme weather so we can prepare and plan smarter.  New technologies are also helping to tackle the root cause of climate change–fossil fuel emissions.  And while there is a global movement in support of fossil fuel reduction, we need more hands on deck and voices heard to navigate ourselves towards a thriving and healthy future we can all be proud of.  In the end, we are all connected and change is coming.  The question remains: what are we doing about it?

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