Alien or non-native wildlife introductions began more than 200 years ago, soon after the Russians first visited Alaska, and continued until just after World War II.
•Rats invaded several islands as recently as World War II.
•Foxes were stocked on islands with bird colonies as late as 1945 for fur ranching.
•Caribou were released on Adak Island in the late 1950s.
Release of non-native animals on islands within any national wildlife refuge is now against state and federal regulations.The havoc created by these island invaders is significant, especially predators such as foxes and rats. Entire seabird colonies were wiped out by just a few hungry animals. For example, foxes arrived at Walrus Island in the Pribilofs across the pack ice sometime during the early 1970s. A large murre colony there was wiped out. In another example, when foxes remain on barrier islands in the Arctic during some summers, nesting eiders vanish.
Upsetting the Balance: Foxes
As early as 1750, Russian merchants intentionally released arctic and red foxes onto many large Aleutian Islands that had seabird colonies. After the Aleutian Islands became a wildlife refuge in 1913, refuge management initially encouraged fox ranching. Between 1900 and 1929, lease-holders and trappers released foxes on islands. By the end of the fox-ranching era, nearly every island with beach access south of the Alaska Peninsula and in the Aleutian Islands was stocked, and ground nesting birds were extirpated or reduced to low population levels over broad ranges.
Farming for Furs
Typically, ranchers released only a few fox pairs on an island. Foxes increased quickly while seabirds were abundant. Trappers then returned to islands a few years later to harvest pelts from the established fox population. Islands varied in the quality of fox habitat that existed after seabird colonies were decimated. Foxes naturally died out or were easily over-trapped on many islands prior to the war. Foxes were the most widespread invasive mammal on the Alaska Maritime refuge and they were the first non-native predator targeted for eradication.
To Save Native Birds
After WWII, the first resident manager in the Aleutians began a program to eradicate foxes from Amchitka Island in the western Aleutians to try to save Aleutian Canada geese and other native species. He cleared the island of introduced foxes by 1960.
Goose No Longer Endangered
The restoration program continued at a slow pace until about the mid-1970s, but since that time foxes have been removed from one or two islands annually. As a result, the population of Aleutian Canada geese grew from 300 to 30,000. The goose was removed from the endangered species list in 2001 largely because of fox eradication and subsequent reintroduction of the birds to these fox-free, former nesting islands.
Bird Numbers Grow on Fox-free Islands
Foxes extirpated several bird species from long-time fox ranching islands, but sometimes remnant populations persisted on nearby offshore islets. Seabirds quickly re-colonized the larger islands after fox eradication. Additionally, waterfowl, shorebirds, ptarmigan, and possibly passerines increase following fox eradication.
Oil Spill Mitigation Monies
Some island restoration has been funded from oil spill monies as a good way to mitigate for oil spills. The Exxon Valdez Oil Spill Trustee Council recognized that the removal of alien foxes could increase populations of black oystercatchers and pigeon guillemots which were harmed by the 1989 spill.
Norway rats are established on at least 13 major refuge islands and numerous smaller islets. Rats extirpate most species of burrow–nesting seabirds and they probably reduce populations of shorebirds and other ground-nesting species. Some refuge islands (near the Alaska Peninsula, and the Pribilof Islands) have endemic small mammals that may be vulnerable to predation and competition by Norway rats.
Rat Prevention Program
A rodent invasion prevention program began in1993. This effort included a shipwreck response plan and actions to increase harbor defenses against invading rats on islands with refuge lands. Visit www.stoprats.com for more information.
Deer mice, arctic ground squirrels, voles and shrews were also introduced to some islands. Although most rat and mice introductions were accidental, other rodents were intentionally stocked by fox ranchers as alternate prey for their furbearers. Arctic ground squirrels were farmed on some islands for the same reasons foxes were raised – as a source of marketable furs. Grounds squirrels prey on eggs and chicks of waterfowl and eggs and chicks of seabirds. Storm petrels and other burrow nesters are absent on islands with ground squirrels. Nearby islands without ground squirrels have these species. It is not always apparent whether ground squirrels occur naturally or were stocked. The U.S. Fish and Wildlife Service is funding a genetics project to help sort out which islands have remnant populations of ground squirrels, and which islands were stocked during the last 100 years. For example, the project compares genetic relatedness of ground squirrels from the Inner Shumagin Islands, where Stellar noted them in 1741, with ground squirrels that appear different and are probably introduced in the Outer Shumagins.
During the last century, cattle, reindeer and caribou were stocked on islands that are now within the Alaska Maritime Refuge, Reindeer, native to Siberia, were stocked in Alaska primarily between 1892 and 1902. Reindeer or caribou have been stocked on seven islands that are partly refuge-owned and partly private land.
Alien to Island Ecosystems
Oceanic island systems did not evolve with large herbivores, and domestic grazers can change the vegetation structure and composition and cause significant erosion. Sometimes abandoned herds on islands die out without further human intervention. As an island reaches carrying capacity for an invasive grazer, annual herd size typically fluctuates with a declining trend because of increasing damage to vegetation and soils. Eventually the population crashes after a severe. In the case of St. Matthew Island, the crash ended with extinction of that herd. In areas further south, such as Atka, die-offs have not resulted in extirpation. The only introduction of caribou on the Refuge was on Adak Island during the late 1950s. Caribou are native to mainland Alaska and occasionally swim to nearby large islands. Like reindeer, caribou tend to overgraze favored areas on islands before moving. On Adak, overgrazing apparently has occurred on the southern, refuge, part of the island. Much of the northern portion has been transferred to the Aleut Corporation.
Cattle persisted from abandoned ranches on about five Refuge islands. Cattle overgrazing can also result in long-term plant community changes and interfere with nesting of native birds, especially shorebirds and waterfowl. Feral island cattle trample nests, compact the soil, and cause down-cutting of streams, lowering of the water table and soil erosion. Burrow-nesting seabirds are directly affected, especially when introduced foxes are established on the same island as cattle. Large populations of ancient murrelets and Cassin’s auklets disappeared from Sanak Island after foxes and cattle were introduced, for example.
And There’s Still More
Other invasive animals on the Refuge include: house mice, deer mice, shrews, marmots, rabbits, and voles. The total acreage where these exotics occur is slight compared with foxes, rats and ungulates. Nevertheless, the Refuge will study where these introduced mammals live to determine their effect on the islands’ natural biodiversity. Another inventory recently underway examines invasive marine invertebrates and plants.
Judging from the response in areas we have monitored, the project to remove alien foxes has likely increased populations of 15 to 20 bird species by more than 200,000. That number should continue to rise for several decades. One endangered species has been restored and several endemic forms saved that formerly had been candidates for the Endangered Species List (Evermann’s rock ptarmigan, for example).
The goal of the refuge’s invasive species program is to protect and restore the natural diversity of refuge islands. The results have been dramatic over the last 50 years. Preventing new introductions of exotics and removing existing infestations are the most effective management actions to protect the native wildlife given in trust to Refuge stewards.