The Pen Islands lie off the Hudson Bay coast at the extreme northwestern corner of Ontario, about 100 km northwest of Fort Severn. The site includes the Pen Islands and the adjacent coastline from Black Duck River to the mouth of the Minitiagan River in the east. East Pen Island is within 5 km of the Manitoba border, while West Pen Island is located about 20 km east of the border. West Pen Island is a low marshy area separated from the mainland only by a narrow waterway at high tide. East Pen Island is separated from the mainland by about 4 km of shallow water at high tide. At low tide, it is practically joined to the mainland. Almost continuous intertidal marshes extend 3 km between East Pen and the mainland, forming the widest expanse of intertidal and supertidal marshes in Ontario. The adjacent coastline contains extensive supertidal marshes, ponds and small lakes for 10 or more km inland.
Upland heath lichen tundra can be found on an area of raised sand ridges that extend along the coast. These beach ridges provide an important calving area for Woodland Caribou, a nationally vulnerable species. This region is also an important summering area for Polar Bears, holding 30 to 40% of Ontarios summering population (about 180 to 218 bears).
One of the largest concentrations of Hudsonian Godwits ever recorded in Canada has occurred at this site. In 1992, a one-day count of 8,800 was recorded. This may have represented as much as 17.6% of the worlds estimated population. Few surveys have been completed at this site to fully evaluate its significance. Red Knots have also been recorded in large numbers, with one-day counts in excess of 2,000 birds (about 2% of the North American [ssp. rufa] population).
In addition to shorebirds, large numbers of waterfowl also utilize this site as a staging, breeding and moulting area. In the summer of 1994, a total of 6,160 moulting Black Scoters was recorded at this site. If these birds were from the eastern population, they would represent as much as 4.4% of the estimated population. It is also a high density nesting area for Snow Geese with the number of nesting geese totaling around 8,000 pairs (1995-97). They use the entire site as a brood rearing area. It has also been noted that significant numbers of Common Eiders (ssp. sedentaria) nest on East Pen Island. Recent surveys, however, have not been completed. A major decline in the Hudson Bay Common Eider population has recently been recorded (possibly as a result of winter kill when the leads and polynyas froze over in 1992). If Common Eiders are still nesting on this island, their numbers will likely be significant.
Conservation responses/actions for key biodiversity
As with all areas inhabited by large numbers of geese in the arctic, there is concern about excessive grazing at this site and its impacts on the wetland vegetation. This site, however, is relatively well protected by ice cover during the early spring when impacts can be most severe. The Pen Islands have been recommended as a Western Hemisphere Shorebird Reserve Network (WHSRN) site of international significance. This recommendation was largely based on the concentrations of Hudsonian Godwits and Red Knots that have been recorded at this site.