Oceans and seas

Hudson Bay

May 14, 2013, 2:11 pm
Content Cover Image

Frozen fringe of Hudson Bay near Churchill. @ C.Michael Hogan

Hudson Bay is a large saline water body connected to the Atlantic Ocean via the Hudson Strait.

The surface area extent, lying entirely within the nation of Canada, covers approximately 1,230,000 square kilometres.

This bay has a low salinity level compared to most of the world's oceans, since there is a large volume of freshwater input from the extensive drainage basin.

caption Hudson Bay. Source: Tim Vasquez

Pack ice forms over much of Hudson Bay each winter, altering the environment for its marine mammals and micro-biota. Polar bears require the pack ice to pursue their winter predation at sea, while some of the pinnipeds and cetaceans are severely restricted from occupartion of heavy ice pack areas. A surprising assortment of wildlife have adapted to the severe icy conditions of Hudson Bay and the adjoining Hudson Plains ecoregion. The Southern Hudson Bay taiga ecoregion extends along the lowlands adjacent to Hudson Bay from Manitoba, though Ontario and into a small part of western Quebec next to James Bay. The Eastern Canadian Shield taiga stretches from Hudson and James Bay to southern Ungava Bay to the north, and the Atlantic Ocean to the east.

Geography and Hydrology

Canadian provinces rimming Hudson Bay are Nunavut, Manitoba, Ontario and Quebec; moreover, parts of Alberta and Saskatchewan also drain to this mammoth bay. The customary definition of the northern limit of Hudson Bay is: A straignt line extending from the Nuvuk Islands 62 degrees 21 minutes North; 78 degrees six minutes West to Leyson Point, which the southeastern extremity of Southampton Island; thence a new line continues along the southern and western shores of Southampton Island to its northern point; finally a third line to Beach Point on the Canadian mainland. caption Hidson Bay surface currents. Source: Philippe Rekacewicz & Emmanuelle Bournay, GRID-Arendal

The average depth of Hudson Bay is only about 125 metres, and the bottom topography is relatively gentle, except for rugged elements along parts of the eastern fringe. The shallowness of sill and channel depths with the Atlantic Ocean limit the exchange of waters between Hudson Bay and the Atlantic. Summer and autumnal circulation within Hudson Bay is cyclonic with an anti-clockwise gyre; autumn cyclonic current velocity has been measured at roughly five centimetres per second. Winter circulation is less well known, partially because of the pervasive pack ice. Waters entering Hudson Bay from the Atlantic are denser than those of Hudson Bay; therefore, such denser waters sink to the bottom of Hudson Bay and do not participate in surface flow in a substantive way. A number of freshwater rivers also discharge to Hudson Bay, such as the Churchill River.

Marine Ecosystem

See also Arctic marine environments and Climate change and terrestrial wildlife management in the Canadian North

Invertebrates and Flora

Surprisingly there is a diverse ecosystem beneath the ice surface consisting of an assemblage of microflora appended to the lower ice surface, when it is present in a given season and reach of the bay.These micro-algae assemblages grow patchily in response to variations in salinity, temperature and sunlight penetration of the pack ice. In turn a diverse group of micro herbivores is found at the ice bottom; furthermore, in the lower three centimetres of surface ice there is a range of rotifers, nematodes, ciliates and copepods; these faunal ice dwellers are less diverse than the micro-algae community, but denser in biomass.

There is a pronounced seasonal sub-ice algae bloom, followed by a burst of productivity of the micro-herbivores and other fauna. The climax of biological activity produces a rain of dead cells and even living organisms, some of which reach the benthos, but most of which circulate in the pelagic water column, forming a food supply for pelagic organisms. Calanus glacialis and Pseudocalanus minutus are two of the marine planktonic copepods that feed upon the ice algal blooms.

caption Frozen pond near Churchill, part of the extensive wetlands of western Hudson Bay
@ C.Michael Hogan

The intertidal and near shore areas of Hudson Bay are generally depauperate in invertebrates due to the freezing winter temperatures as well as the scouring and crushing of the pack ice.


caption Polar bear beginning his winter migration onto the Hudson Bay ice
@ C.Michael Hogan
Many of the mammals of Hudson Bay are migratory and seasonal visitors. The Harp seal (Pagophilus groenlanicus) and Hooded seal (Cystophora cristata) are pinnipeds that are restricted from the parts of Hudson Bay in winter when pack ice restricts access to air. However, the Atlantic walrus (Odobenus rosmarus ssp rosmarus), Bearded seal (Erignathus barbatus), Ringed seal (Pusa hispida) and Harbour seal (Phoca vitulina) are year round residents to at least portions of Hudson Bay.

Six cetaceans are found in Hudson Bay, including the Narwhal (Monodon monoceros), Beluga (Delphinapterus leucas), Bowhead (Balaena mysticetus), Killer (Orcina orca), Northern Minke (Balaenoptera acutorostrata) and Humpback whale (Megaptera novaeanglia). The first three whale species can actually overwinter in Hudson Strait or sometimes on polynas (areas of open water surrounded by sea ice) within the bay. There is a pronounced geographic bias on the distribution of some of these cetaceans within Hudson Bay; for example, Belugas are strongly associated with the western part of Hudson Bay, with significant attraction to estuaries such as the Churchhill River.

Perhaps the most iconic mammal frequenting Hudson Bay is the Polar bear (Ursus maritimus), who enters the pack ice in early November after denning season. The Arctic fox (Vulpes lagopus) also is found on coastlines in the summer and even ventures out on th pack ice margin in winter.


caption Pair of Willow ptarmigans on the Hudson Bay fringe. @ C.Michael Hogan

The only bird species present year around in Hudson Bay is the Hudson Bay eider (Somateria mollissima sedentaria), which is adapted to access benthic prey in polynyas, where significant sea currents keep the water suface ice free year around. Certain other birds winter farther south such as the Thick-billed murre (Uria lomvia). Other near shore birds present that are known to be occasionally stalked by the Polar bear are Canada goose (Branta canadensis) and Barnacle goose (Branta leucopsis). The Eskimo Curlew (Numenius borealis) has historically been a Hudson Bay migrant, but this taxon is now potentially extinct due to habitat loss. Other bird taxa seen around the edges of Hudson Bay are Gray Jay (Perisoreus canadensis), Gyrfalcon (Falco rusticolus) and Willow Ptarmigan (Lagopus lagopus), all of whom are adapted to withstand the winter in some of the milder parts of the Hudson Bay perimeter.

Certain bird species have significant sized summer breeding colonies in Hudson Bay; for example, the Lesser snow goose (Chen caerulescens ssp. caerulescens) has a very large breeding colony at Cape Henrietta Maria, a landform jutting into Hudson Bay at the northwestern tip of James Bay.

Terrestrial Ecosystem

caption Black spruce forest edge near World War II radar base. @ C.Michael Hogan

The adjacent terrestrial ecosystems are more significant in this region than certain others, since the line between terrestrial and aquatic species is blurred by the widespread pack ice during winter. The Hudson Plains ecoregion is centered in northern Ontario and extends into northeastern Manitoba and western Quebec. Wetlands cover 90 percent of this ecological region, making it the largest wetland-dominated area of North America. In fact, this region contains the longest stretch of shallow, emergent wetland shoreline on Earth. Furthermore, much of the terrestrial ecosystem is governed by presence of permafrost and tundra.

Much of the drainage basin is dominated by Black spruce (Picea mariana) forest, although in the more northern reaches, the trees are typically stunted and ice pruned, due to the severity of the cold and high winds characteristic of the Hudson Plains. The forest understory is rich in scrub willow and a gamut of lichen and feathermoss species.


The prehistory of the Paleoeskimo people is linked to migration over the Bering icebridge by their Siberian ancestors. These early peoples may not have moved eastward into the Hudson Plain until about 4500 to 2500 years before present; artifacts discovered leads to the assertion that these early peoples subsisted chiefly by hunting; foruthermore, the nature of the implements discovered implies a reliance upon marine hunting including seal and walrus; however, there is also ample trace of bow and arrow hunting for Arctic fox, Polar bear and Muskox.

There is evidence that the long term global warming trend during the Holocene hindered and led to adaptations of hunting styles of the early inhabitants. Terrestrial hunting apparently decreased during the Dorset period beginning about 800 BC. Eventually the Thule people drove out or marginalised the Dorset culture about 1000 AD, well before Europeans arrived in the region.

Hudson Bay was initially explored in detail by the English navigator Henry Hudson, in 1610; the bay evolved into a shipping route of great significance for establishing European colonies and trading with indigenous peoples within Canada.


  • Torsten Bernhardt. Hudson Plains. Canada's Ecozones, Canadian Biodiversity project. McGill University, Redpath Museum
  • Bird Studies Canada. Taiga Shield and Hudson Plains. Canadian Bird Conservation Regions.
  • Environment Canada. The Wetlands. Hudson Plains Ecozone.
  • Steven H.Ferguson, Lisa L.Loseto, Mark L.Mallory. 2010. A Little Less Arctic: Top Predators in the World's Largest Northern Inland Sea, Hudson Bay. Springer. 288 pages
  • Ireneo Peter Martini. 1986. Canadian inland seas, Volume 44. 494 pages
  • C.Michael Hogan. 2008. Polar Bear: Ursus maritimus, Globaltwitcher.com, ed. Nicklas Stromberg
  • Anna Marie Prentiss, Ian Kuijt, James C.Chatters. 2009. Macroevolution in Human Prehistory: Evolutionary Theory and Processual Archaeology. Springer. 324 pages





Hogan, C. (2013). Hudson Bay. Retrieved from http://www.eoearth.org/view/article/153582


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