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Tracking a behemoth

Learning more about the Greenland shark helps researchers better understand Arctic ecosystems
April 22, 2009
Fisk maneouvres a boat off the shores of
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Fisk maneouvres a boat off the shores of Cumberland Sound, Nunavut, where he examines the effects of climate change on food webs.
Rob Currie

(With permission from the University of Windsor)

Changing ice conditions caused by climate change in the area of Baffin Island is increasing the competition between Inuit hunters and polar bears for ringed seals, a traditional source of food for both.

An animal that is not being considered in this struggle for survival and that may be playing a significant role in Arctic ecosystems is the enigmatic Greenland shark, says a University of Windsor researcher.

“Polar bears and the Inuit people both need ice to capture ringed seals, but the Greenland shark isn’t restricted by these limitations,” says Aaron Fisk, an associate professor at the university’s Great Lakes Institute for Environmental Research (GLIER). “Reduced ice levels may be working to the shark’s advantage.”

Fisk travels more than 3,000 kilometres several times a year to a remote corner of the island near Cumberland Sound. He uses techniques such as global positioning and tissue sample analysis to study the shark’s feeding habits during times of ice cover and open water conditions.

A captured Greenland shark hangs from a fishing
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A captured Greenland shark hangs from a fishing vessel off the coast Svalbard, Norway.
Christian Lydersen

Little is known about the Greenland shark, which can grow up to seven metres long and may live to be 200-years-old, though Fisk’s research, which is partially funded by International Polar Year, is examining how it fits into the polar ecosystem.

Fisk and his team examine tissue samples taken from sharks caught in fishing lines for chemical tracers — stable isotopes of carbon, nitrogen, omega-3 fatty acids and contaminants such as mercury — to obtain molecular evidence of the animals’ diets. Though researchers prefer a less invasive approach, they occasionally must sacrifice a shark to examine the contents of its stomach.

In addition to collecting tissue samples, Fisk tags sharks with global positioning devices to collect data on migratory patterns and depth travel. After several months, the tags detach from the shark and float to the ocean’s surface, where data is transferred to a satellite and back to the research lab for analysis.

Fisk’s work caught the attention of Discovery Channel’s Dirty Jobs producers, who sent host Mike Rowe and his crew on location to the extreme conditions of Fisk’s northern outdoor laboratory last spring to film. The episode, which aired in July during the network’s annual Shark Week, showed one of Fisk’s graduate students explaining why sharks must sometimes be sacrificed for research.

“If you’re trying to manage a species, you need to know what they’re eating,” says Fisk, who is also a Canada Research Chair in Trophic Ecology. “Understanding the impact of Greenland sharks on these marine mammals is needed for future management of these populations and marine ecosystems in general. If ringed seals are to continue to be a central component of the Inuit culture and diet in a changing Arctic, we need to be able to manage the ecosystem. In order to manage it, you need to understand it as best you can.”