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Site description (2001 baseline):

Amphitrite Bank and Swiftsure Bank are two small areas of rich productive water off the west coast of Vancouver Island, British Columbia. Amphitrite Bank (approximately 90 km2) is about 6 km southwest of Ucluelet, and Swiftsure Bank (18 km2) is separate and further to the south, being about 15 km southwest of the western end of Nitinat Lake. These two areas of relatively shallow water are roughly defined by the 50 m isobath the shallowest water is generally less than 35 m. The latitude and longitude noted above denote a point in between the two banks, and thus it is not actually in the IBA. The north and south limits of Amphitrite Bank are 48°54N and 48°48N, whereas the centre of Swiftsure Bank is about 48°33N and 125°00W.

Amphitrite Bank and Swiftsure Bank are known for their abundance and diversity of coastal and pelagic seabirds. The majority of species are most abundant from June through September. Four species of marine birds, two tubenose species (Procellariidae) and two gull species are either particularly numerous or are found in significant numbers.

Northern Fulmars are common around factory ships during late summer and early fall. Flocks of between 5,000 and 10,000 birds have been observed over both Amphitrite and Swiftsure banks. These birds are thought to be a mixture of non-breeding adults, failed breeders and immature birds. Shearwaters are also abundant in late spring, early summer, and again from September through mid-October, the non-breeding season for Sooty and Short-tailed shearwaters. On one occasion a flock of approximately 12,000 Sooty Shearwaters was seen over Swiftsure Bank in June.

California Gulls can be seen between May and November, but progressively become more abundant as the summer and fall advance. A single large flock that was estimated to contain 15,000 birds was seen over Swiftsure Bank in August 1989; it is thought that the birds were associated with factory ships. This species is the most abundant species in the fall. The largest flock in this season was recorded in September 1986 when between 10,000 and 12,000 were seen feeding on schools of small fish in Swiftsure Bank. Sabines Gulls may be seen between May and October, but they are most abundant in late August and September. Large flocks of this species were seen at Swiftsure Bank in September 1986 (975) and August 1989 (620). These numbers are almost certainly over 1% of the Canadian Sabines Gull population and may also be over 1% of the unknown North American population.

Other birds recorded here in high numbers include: Cassins Auklets (6,000 at Amphitrite Bank in August 1986), Common Murres, Rhinoceros Auklets, Tufted Puffins, Herring, Thayers and Glaucous-winged gulls Black-legged Kittiwakes, jaegers, phalaropes, and other procellariids.

As with many coastal or oceanic areas, oil spills are a potential hazard to oceanic birds. Large factory boats attract many pelagic birds, because they discharge offal and other unwanted fish parts, and thus are part of the reason that pelagic birds are so abundant in these areas. On the other hand, there are other aspects of the fishing industry that can negatively affect marine birds: birds can drown after becoming entangled in gillnets or longline hooks, and over-fishing could potentially negatively affect pelagic bird populations.

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Recommended citation
BirdLife International (2024) Important Bird Area factsheet: Amphitrite and Swiftsure Banks (Canada). Downloaded from https://datazone.birdlife.org/site/factsheet/amphitrite-and-swiftsure-banks-iba-canada on 23/11/2024.