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Ecology

Greenland sharks: Caught on tape for conservation

In 2016 researchers discovered that Greenland sharks (Somniosus microcephalus) are the oldest living vertebrates on the planet. What does that mean for the conservation and management of these large, cold-water predators? This week we’ll find out.

Devine, B.M., L.J. Wheeland, and J.A.D. Fisher. 2018. First estimates of Greenland shark (Somniosus microcepahlus) local abundances in Arctic waters. Scientific Reports 8:974. https://doi.org/10.1038/s41598-017-19115-x

What are Greenland Sharks?

Greenland sharks are the largest fish in the Arctic and one of the few known polar shark species. They live throughout the Arctic and North Atlantic Oceans, where they are top predators. Some have even been found with remains of polar bears and reindeer in their stomachs!   To top it all off, most adult Greenland sharks are virtually blind because of a copepod parasite that attaches to their cornea. Much is unknown about Greenland sharks, but recently scientists discovered that they can live for hundreds of years. Using bomb radiocarbon dating scientists determined that these sharks don’t mature until they are over 14 feet long and 134 years old and they can live for more than 270 years! To put it simply, Greenland sharks are an amazingly weird feat of biology!

A Greenland shark swims through cold Arctic waters. Can you see the copepod parasite on its cornea? (Photo credit: Wikimedia Commons)

Because they take so long to mature and live for such a long time, Greenland shark populations are exceptionally vulnerable to things like overfishing and mortality from bycatch, accidental capture in a fishery focused on other species. Greenland sharks are considered data deficient through much of their range, meaning scientists don’t know much about how many sharks there are in that area and what types of habitats are important to them. A lot of what we do know about Greenland shark populations is fishery dependent, coming from bycatch data and past commercial fishing records. Until 1960, Greenland sharks were targeted for their liver oil, in Greenland and Norway, and they are still caught today and used for sled dog meat. Greenland sharks are also commonly caught as bycatch in the Greenland halibut fishery.

There are currently exploratory fisheries for Greenland halibut opening in the Canadian Arctic as well as the establishment of the Lancaster Sound National Marine Conservation Area, a protected area which preserves habitats from oil and gas exploration. Armed with this information, researchers from the Fisheries and Marine Institute of Memorial University of Newfoundland in Canada set out to determine how many Greenland sharks might be living in this area.

What did they do?

To study and count Greenland sharks in their natural habitat, Brynn Devine and her research team used Baited Remote Underwater Video (BRUV). BRUVs are exactly what they sound like, a waterproof camera attached to a long pole and a cage of bait. The camera can record anything that swims by the bait box. They can even be equipped with two lasers spaced a fixed distance apart allowing scientists to estimate the length of the animals they observe. The advent of GoPros and other relatively inexpensive cameras with waterproof housings makes them an affordable tool for research, and best of all they’re non-invasive so they don’t cause any stress to the animal or damage to the habitats where they are deployed. From July – September in 2015 and 2016, 31 BRUV deployments were conducted in the Canadian territory of Nunavut at five study sites: Arctic Bay, Lancaster Sound, Resolute, Jones Sound, and Scott Inlet. These sites all fell within the range of exploratory fisheries for Greenland halibut across a variety of depths and habitats.

Locations of the 31 BRUV deployments in Nunavut, Canada scaled by the number of sharks observed on each deployment (Devine et al. 2018).

After retrieving the cameras, the research team went through the footage, recording the arrival time of each Greenland shark and identifing individuals. Similar to how cetacean researchers can identify humpback whales based on the white and black pattern on the underside of their tails, Greenland sharks have easily distinguishable markings, combinations of scars and coloration patterns. Because of this, they were able to determine if they were seeing the same individual at multiple sites. Researchers also measured each shark and determined its sex based on the presence or absence of claspers, the male external sex organ in sharks. After all of this data was collected, the team used equations to calculate abundance estimates for each region.

What did they find?

Greenland sharks were recorded during 25 of the 31 BRUV deployments and researchers identified 142 individuals. Observation rates were highest in the Arctic Bay region, while Lancaster Sound, Scott Inlet, and Jones Sound were similarly occupied, and Resolute had the fewest sharks. Sharks appeared to prefer water temperatures between 0 and 0.5 oC, that’s 32 to 32.9 oF, and depths between 450 to 800 m, 1,476 to 2,624 feet. Sharks tended to arrive to the BRUV faster in Lancaster Sound and Arctic Bay than in Resolute. Using first arrival time, mean swimming speed of the sharks observed, and mean bottom current speed in the region, scientists estimated that Greenland sharks were most abundant in Arctic Bay and Jones Sound (approximately 5 individuals per square kilometer).   This was much higher than Lancaster Sound and Resolute, which had estimates of only 1.6 and 0.4 individuals per square kilometer respectively. In general, there were not large differences in the size or sex of sharks between sampling regions, but Scott Inlet had a higher proportion of small sharks, less than 5 feet long.

Photos of Greenland sharks swimming by (A, C-E) and interacting with the BRUV (B). You can see the unique coloration and scarring on each (Devine et al. 2018).

Why does it matter?

These are the first abundance estimates made for Greenland sharks in a fishery independent survey (i.e. the data did not rely on a fishery to be collected). There is still much that we don’t know about the abundances of Greenland sharks in the Arctic and North Atlantic, but this research brings scientists one step closer to understanding how many sharks are out there, which is incredibly important given their long lifespan and susceptibility to being caught in other fisheries. Arctic Bay, Jones Sound, and Scott Inlet seem to be particularly important areas for these sharks during the summer and this should be taken into account when developing fisheries in the area. Greenland sharks are highly migratory so there maybe large seasonal changes in the habitats they use. The research team stressed the importance of more camera deployments throughout the year to better understand seasonality and variation between years. Many of these sites fall within the boundaries of the Lancaster Sound National Marine Conservation Area so understanding how Greenland sharks use these regions and non-protected areas is essential for making effective management decisions. Scott Inlet is particularly interesting because of the presence of small sharks and it could be a nursery area for young Greenland sharks during the summer months.

The ability to identify individual Greenland sharks based on their markings means that scientists might be able to track the movements of individual sharks through repeated observations on BRUVs in future studies. This has already been done with white sharks (Carcharodon carcharias) and whale sharks (Rhincodon typus).

Finally, the abundance estimates from Greenland sharks in the Nunavut territory, Canada, a relatively untouched environment, are similar to those made for other shark species in relatively pristine tropical reefs. We know that sharks on reefs play an important role in balancing the coral reef food web, and as the only large fish predator in the Arctic, Greenland sharks are likely just as essential to the ecosystem. This research is an essential step towards conserving these ancient Arctic sharks.

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