San Juan Islands - Ecology

Ecology

The islands were heavily logged in the nineteenth century but now have an extensive second-growth Coast Douglas fir (Pseudotsuga menziesii var. menziesii), Pacific madrone (Arbutus menziesii), Red alder (Alnus rubra) and Bigleaf maple (Acer macrophyllum) forest. There are rare stands of old-growth Douglas fir and Western Redcedar (Thuja plicata). In the highlands one also finds Grand fir (Abies grandis), Western hemlock (Tsuga heterophylla) and other subalpine trees.

The San Juan Islands host the greatest concentration of Bald Eagles (Haliaeetus leucocephalus) in the continental United States. Great Blue Herons (Ardea herodias), Black Oystercatchers (Haematopus bachman), and numerous shorebirds are found along the shore and in winter, the islands are home to Trumpeter swans (Cygnus buccinator), Canada goose (Branta canadensis) and other waterfowl. Peregrine falcons (Falco peregrinus), Northern harriers (Circus cyaneus), Barred owls (Strix varia) and other birds of prey are found. In addition diving birds such as Rhinoceros Auklet (Cerorhinca monocerata), Pigeon Guillemots (Cepphus columba) and endangered Marbled Murrelet (Brachyramphus marmoratus) frequent the surround seas. Western Bluebirds (Sialia mexicana), who went extinct 50 years ago because of competition for nesting sites by non-native European Starlings (Sturnus vulgaris), were recently restored to San Juan Island thanks to the efforts of volunteers and conservation organizations.

The islands are famous for their resident pods of Orcas (Orcinus orca). There are three resident pods that eat salmon but also some transient orcas that come to take Harbor seals (Phoca vitulina). Other marine mammals include the River otter (Lontra canadensis), Steller sea lions (Eumetopias jubatus), Common minke whales (Balaenoptera acutorostrata), Dall's porpoise (Phocoenoides dalli) and other cetaceans.

Columbia Black-Tailed Deer (Odocoileus hemionus columbianus) are the largest mammals on the San Juan Islands, which are unusual in their absence of large carnivores historically, except for wolves (Canis lupus) which were extirpated in the 1860s. Dr. Caleb B. R. Kennerly, surgeon and naturalist, collected a wolf specimen on Lopez Island which is in the National Museum of Natural History, probably collected during the Northwest Boundary Survey from 1857-1861. Also there is a specimen of Elk in the Slater Museum of Natural History at the University of Puget Sound that was collected historically on Orcas Island, and old timers report finding elk antlers on both Lopez and Orcas Islands.

Before 1850, most of the freshwater on the islands was held in beaver (Castor canadensis) ponds, although the aquatic mammal was extirpated by Hudson's Bay Company fur stations at Fort Langley and San Juan Island. Remnants of beaver dams number in the hundreds across the archipelago. Gnawed stumps and beaver sign are now seen on Orcas and other islands, and recolonization by this keystone species is likely to lead to increased abundance and diversity of birds, amphibians, reptiles and plants. In spring, 2011 a pair of beaver appeared at Killebrew Lake on Orcas Island, but were killed to avoid flooding a phone company switch box buried under Dolphin Bay Road. These beaver likely swam from the mainland and could have recolonized the islands.

Northern Sea Otter (Enhydra lutis kenyoni) remains are documented on Sucia Island in the San Juan Islands archipelago. In 1790, Spanish explorer Manuel Quimper traded copper sheets for sea otter pelts at Discovery Bay, for live sea otters captured north of the bay in the “interior” of the Strait of Juan de Fuca. Although historical records of sea otter in the San Juan Islands are sparse, there is a sea otter specimen collected in 1897 in the "Strait of Fuca" in the National Museum of Natural History. When the sea otter finally received federal protection in 1911, Washington's sea otter had been hunted to extinction, and although a small remnant population still existed in British Columbia, it soon died out. Fifty-nine sea otters were re-introduced to the Washington coast from Amchitka Island, Alaska in the summers of 1969 and 1970 and these have expanded by 8% per year mainly along the outer west and northwest coast of the Olympic Peninsula. Professional marine mammal biologists verified a single sea otter observed near Cattle Point, San Juan Island in October 1996. Although the historical numbers of sea otter in the San Juan Islands is not known, the habitat for them may have once been ideal.

In the 1890s non-native European rabbits, an exotic invasive species, began to infest the islands as the result of the release of domestic rabbits on Smith Island. Rabbits from the San Juan Islands were used later for several introductions of European rabbits into other, usually Midwestern, states. The rabbits are pursued by Eurasian Red Fox (Vulpes vulpes), another non-native species introduced intermittently through the twentieth century.