Mitlenatch Island is located in the northern Georgia Strait, about 4 km south of Cortez Island. At this location, the tides from the north and south ends of Vancouver Island meet, which increases the biological richness of the surrounding waters. The 35.5 ha island is mostly basaltic rock that forms two prominent hills. Between these two hills is a 2.5 ha meadow, and along the northwest and southeast ends of this meadow are gravel beaches. The rest of the island has a varied terrain with exposed rises and knolls.
The island is vegetated with grasses, forbs, shrubs, and wooded areas that can withstand dry conditions. A prolonged summer drought resulting from the rain shadow effect of Vancouver Island allows several rare Gulf Island plants to live on the island such as Prickly Pear Cactus, Blue Camas, Sea Blush, and Easter Lily. In addition to rare plants, about 50 to 100 non-breeding Stellers Sea Lions and about 10 to 20 non-breeding California Sea Lions use the site in both the spring and summer. Wandering Garter Snakes are also common.
Mitlenatch Island supports the second largest seabird colony in the Strait of Georgia. At least three bird species nest in significant numbers on the island: Pelagic Cormorant (about 7.4% of the estimated National population); Glaucous-winged Gull (just over 1% of the estimated North American population, and as much as 8.4% of the estimated national population); and Pigeon Guillemot (just over 1% of the estimated national population). In addition, as many 300 Marbled Murrelets have been observed foraging around the island during the summer. Marbled Murrelets have been identified as nationally threatened.
Mitlenatch Island also supports about 8 pairs of Black Oystercatchers, 50 pairs of Northwestern Crows, and is an important moulting site for post-breeding Harlequin Ducks. It has been a study area for various bird research programs since the 1960s. The IBA should include the surrounding marine area to at least a five km radius, since this area is important for wintering grebes and scoters.
BirdLife International (2020) Important Bird Areas factsheet: Mitlenatch Island. Downloaded from http://www.birdlife.org on 03/12/2020.