by: Jim Reist
In late summer of 2019 a Salmon Shark (Family Lamnidae, Lamna ditropis) was captured in the marine waters of the central Canadian Arctic (a few kilometers north of Kugluktuk). The Salmon Shark is normally a species found in temperate and sub-arctic Pacific Ocean waters, so finding one in Arctic waters is quite unusual. Right now this is being characterized as an extreme extra-limital occurrence. However, this isn't the only example of recent changes occurring in the Canadian Arctic marine ecosystem.
Above: Salmon Shark (a species newly recorded from the Arctic) by Kugluktuk resident, John Kapakatoak
Sharks are fusiform-bodied fishes with cartilaginous rather than bony skeletons. Five species of shark are documented as normally occurring in Canadian Arctic or sub-arctic marine waters - the Greenland Shark, Portuguese Shark, Black Dogfish and Deepsea Cat Shark. These are found in Davis Strait/Baffin Bay in the eastern Arctic. Only the Pacific Sleeper Shark is known to occur in the Canadian Beaufort Sea in the western Arctic.
These shark species are typically found in deep-water habitats during the open-water season, but in winter may venture near coasts on shallow shelves seeking food. This is especially true for the Greenland Shark, which can be quite large (up to 6 m in length). Previous distributional records exist for Greenland Shark in some locations in eastern Hudson Bay, however, one individual was captured at Coral Harbour in 2018 in northwestern Hudson Bay and is the closest record to Manitoba waters for any shark species.
A number of unusual events occurred in the Arctic in both 2018 and 2019.
This year, an unprecedented number of Pacific salmon of various species were captured by Indigenous fishers in many locations of the western Arctic and as far east as Kugluktuk. So far around 3000 samples have been turned in to the Arctic Salmon project, which has been monitoring the increasing occurrences of salmon since 2000. Of the five species of Pacific salmons that typically occur in temperate and sub-arctic waters of the west coast of Canada and Alaska, only one is known to have small reproducing populations in the Mackenzie River basin of the western Arctic. Until recently, the remaining four species were documented only as occasional vagrants (i.e., unusual distributional occurrence) to Canadian Arctic waters.
Increased numbers of all species have been generally occurring, with high variations in numbers from year-to-year. 2019 was exceptional. Pacific salmons have also shown progressively increasing distributions of occurrences in more easterly waters of the Arctic Archipelago but, as yet, no new colonizing populations have been observed.
So, what is happening? Like elsewhere in the country, Canada’s Arctic marine ecosystems appear to be undergoing substantive and relatively rapid changes. These changes likely include altered marine conditions such as warming ocean waters, unusual shifts in movements of marine water masses, and associated changes in the ecosystem structure (such as altered distributions and occurrences of species not previously known from the area). These changes appear to be affecting the western Arctic more substantively and sooner than waters in the east.
The Canadian Beaufort Sea is normally made up of layers of water. Each layer originates from a different location and has different levels of salinity and different temperatures. In summer the top 50 meters is relatively freshened sea-ice meltwater and river runoff. Below this (between 50 and about 250 meter depths) the water layer originates from the North Pacific Ocean (Bering Sea), and is relatively warm, nutrient-rich and lower in salinity. Additional water layers exist at deeper depths.
The two combined surface layers generally move eastwards across shallow sills into and through the passages of the Canadian Archipelago, ultimately exiting into Baffin Bay and Davis Strait. These surface water currents connect areas of the North Pacific to those of the Archipelago, and ultimately the Northwest Atlantic. In theory they provide a marine ‘highway’ for fishes and other biota.
Different water layers are preferred habitats for distinctly different groups of fish species. Pacific salmon and the Sleeper Shark prefer the upper surface layers because of warmer temperatures and better feeding. Whereas adults of most Arctic species tend to prefer bottom areas in deeper waters. In recent years greater amounts of Pacific-origin water are entering the western Canadian Arctic, moving eastwards, and likely carrying plankton prey preferred by salmon. In turn, the salmon are following their prey and similarly the Salmon Shark is following its prey. Parallel shifts in the Arctic generally towards less sea ice overall, warmer marine waters in summer, and greater pelagic (water column) productivity also appear to aid these outcomes, further enhancing the suitability of Arctic waters for at least some sub-Arctic fishes. This is thought to explain occurrences of increasing numbers of Pacific salmon over wide areas of the western and central Arctic, and in 2019 the Salmon Shark occurrence.
Climate variability and change is substantively altering the Canadian Arctic marine ecosystems, and is ultimately the driving force behind these unusual occurrences. Previously, 221 species of fishes including the salmons were known to occur in Canadian Arctic marine waters and the Salmon Shark increases this to 222. This number is expected to increase as additional ecosystem shifts associated with climate change take hold and additional sub-arctic fishes colonize the area.
Continued monitoring through Arctic Salmon and other programs will provide more examples of these unusual events and lead to better understanding of the changes occurring in Canada’s Arctic marine system.
Resource sources for additional information:
Arctic Salmon – https://www.facebook.com/arcticsalmon/
Marine Fishes of the Canadian Arctic. 2018. B.W. Coad and J.D. Reist (eds.). University of Toronto Press.
About the author: Jim Reist is a researcher on ecology, diversity, adaptation, and stressor responses (including responses to climate variability and change) of northern and Arctic fishes in Canada. He is interested in biodiversty, particularly that associated with the most speciose groups of invertebrates – the insects, and vertebrates – fishes. Nearing formal retirement, he is resurrecting early interests in Lepidoptera (butterflies, skippers and moths), Odonata (damselflies, dragonflies) and Coleoptera (beetles) as a focus of activity.