IBA Mitlenatch Island
Strait of Georgia, British Columbia
Site Summary
BC065 Latitude
49.950° N
125.004° W
0 - 54 m
6.69 km²
deciduous woods (temperate), scrub/shrub, desert/semi-desert, coastal cliffs/rocky shores (marine)
Land Use:
Nature conservation and research, Tourism/recreation
Potential or ongoing Threats:
IBA Criteria: Continentally Significant: Congregatory Species, Nationally Significant: Congregatory Species
Conservation status: Provincial Park (including Marine)
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Site Description
Mitlenatch Island is located in the northern Strait of Georgia, about 4 km south of Cortes 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 White Fawn Lily. In addition to rare plants, about 50 to 100 non-breeding Steller's 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.

Significant Species - 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, Glaucous-winged Gull, and Pigeon Guillemot. In 2015, from June 8-14, nests of Glaucous-winged Gull were counted, with a total of 1438 nests plus an additional estimate of 50, for a total nesting adult bird count of 2,976. When nest with no eggs were excluded, there were 1313 nests with eggs, for a total of 2626 birds. Pelagic Cormorant nests and birds were counted from the water in 2015 on three days from May-July, with a high count of 280 nests and 560 birds recorded. Pigeon Guillemots also nest on the island. Counts of birds have ranged from 130-380 from 2011-2015.

Other Species of Conservation Interest - The IBA supports species determined to be Threatened or Special Concern by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC; wildlife species that have been assessed as at risk by COSEWIC may qualify for legal protection and recovery under Canada's Species at Risk Act). Marbled Murrelet (Threatened, COSEWIC; and Endangered, the International Union for Conservation of Nature, IUCN) occurs regularly in the IBA with counts up to 300 observed foraging around the island during the summer. Peregrine Falcon (Special Concern, COSEWIC) is occasionally seen in the IBA.

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. Double-crested Cormorants are a recent addition to the nesting populations. Since 1993, they have been nesting along cliffs immediately above the Pelagic Cormorants. Their nest counts vary - in 2015, 31 were counted. A pair of Common Ravens has been nesting on Mitlenatch since at least 2005. In 2015, they successfully fledged four chicks. A pair of Virginia Rail have nested on the island since 2008.

IBA Criteria
SpeciesT | A | I Links Date Season Number G C N
Marbled Murrelet 1995 SU 300
Pelagic Cormorant 2013 FA 530
Pelagic Cormorant 2015 - 2019 SP 557 - 838
Pelagic Cormorant 1982 - 2018 SU 560 - 1,200
Note: species shown in bold indicate that the maximum number exceeds at least one of the IBA thresholds (sub-regional, regional or global). The site may still not qualify for that level of IBA if the maximum number reflects an exceptional or historical occurrence.
Conservation Issues
Mitlenatch Island is designated as a Class A Provincial Park by the British Columbia government. The boundaries of the park include not only the island, but also extend 300 m. beyond high tide line into the marine area. Nonetheless, one of the key conservation issues is the disturbance of the nesting seabirds by boaters. However, through the use of both a volunteer warden program and enforcement program, the park appears to be dealing effectively with this problem. Each year, about 2,000-3,000 visitors travel to the island. This rate of visitation has remained constant over the past two decades.

The IBA Program is an international conservation initiative coordinated by BirdLife International. The Canadian co-partners for the IBA Program are Birds Canada and Nature Canada.
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