The following thread focuses on the brown bears (Ursus arctos or the geographical taxon Ursus arctos sitkensis) of Admiralty, Baranof, & Chichagof (ABC) Islands.
The Alexander Archipelago is a 300 miles (500 km) long archipelago, or group of islands, of North America off the southeastern coast of Alaska. It contains about 1,100 islands, which are the tops of the submerged coastal mountains that rise steeply from the Pacific Ocean. Deep channels and fjords separate the islands and cut them off from the mainland. The northern part of the Inside Passage is sheltered by the islands as it winds its way among them.
The islands have irregular, steep coasts and dense evergreen and temperate rain forests.
The largest islands are Chichagof Island, Admiralty Island, Baranof Island, Wrangell Island, Revillagigedo Island, Kupreanof Island, Dall Island and Prince of Wales Island. All the islands are rugged, densely forested, and have an abundance of wildlife.
The Tlingit and Kaigani Haida people are native to the area. The Tsimshian people found on Annette Island are not originally from the area, having immigrated to the region from British Columbia in the late 19th century.
Ketchikan on Revillagigedo Island and Sitka on Baranof Island are the largest towns on the islands. The most populous neighborhoods of the largest town in the region, Juneau, are on the mainland, though portions of the city also lie on Douglas Island, which is a part of the archipelago.
Tourism, fishing, and logging are the main industries of the islands.
Brown bears (Ursus arctos) inhabit the mainland of southeast Alaska and the islands north of Frederick Sound. Greatest numbers occur in Alaska Game Management Unit 4, the ABC (Admiralty, Baranof, and Chichagof) islands, where about 70 percent of the southeastern harvest is taken. Average sport harvests increased from 51 bears per year (1949-56) to 60 per year (1962-72) to 141 in 1975. Other pertinent harvest statistics have remained fairly consistent since 1949; average skin size (length plus width), 4.1 m; average skull size (length plus width), 54.6 cm. Based on dental annuli, ages of males have averaged 8.1 years since 1968. The highest mean annual age was 9.4 years in 1976. The goal of management is to maintain a high-quality hunting experience, which an annual harvest rate of 60-80 animals per year will do much to provide. Harvest statistics gathered over the past 30 years will provide guidelines to insure that management plans are biologically sound. Current regulations that should limit the harvest to desired levels are a $25 tag fee for resident hunters and a limit on the number of guides who can operate in Unit 4. If these fail, time-space zoning, further restrictions on guides, or ultimately permit-only hunting will be necessary. Transfer of nearly 151,760 ha to private land through the Alaska Native Claims Settlement Act and continuing large-scale clearcut logging further cloud the management issue, but with prudent management policies, high-quality and reasonably high-quantity brown bear sport hunting should be possible for many years to come.
Johnson, Loyal. 1980. Brown bear management in southeastern Alaska. International Conf. Bear Res. and Manage. 4:263-270.
From fall 1981 through fall 1985, 58 radio-collared brown bears (Ursus arctos) were followed to winter dens on Admiralty and Chichagof islands in southeast Alaska. One hundred twenty-one dens were located and their site characteristics described. Mean dates of den entry and emergence, 30 October and 2 May, varied between sexes and among years. Mean elevation and slope of 121 dens were 640 m and 35°, respectively. Dens were at higher elevations and on steeper slopes on Admiralty Island than on Chichagof Island. Females denned on higher and steeper slopes than males. Admiralty Island bears preferred subalpine and alpine/rock habitats and Chichagof Island bears preferred old-growth forest for denning. On Admiralty, rock caves were the most frequent den type; on Chichagof, bears excavated dens most frequently under large-diameter Sitka spruce (Picea sitchensis) or in the bases of large snags. Mine development on Admiralty Island may have caused bears to avoid certain denning areas. Industrial scale logging may reduce brown bear denning habitat in this region. Management recommendations for reducing the impact of human activity and resource development on denning brown bears are provided.
Schoen, John W., Beier, Lavern R., Lentfer, Jack W., and Johnson, Loyal J. Denning ecology of brown bears on Admiralty and Chichagof Islands. 1987. International Conf. Bear Res. and Manage. 7:293-304.
There's something different about the brown bears of Southeast Alaska's ABC islands.
They look like your average Alaska grizzly: milk-chocolate colored fur, a humped back, and a size and reputation that gives humans something to fear when walking the wilds of Alaska.
The difference in the brown bears of the ABC (Admiralty, Baranof and Chichagof) islands isn't visible. It's in their DNA. Researchers found the bears are more closely related to polar bears than they are to other brown bears.
The bears' baffling background was discovered when Gerald Shields and Sandra Talbot of the University of Alaska Fairbanks Institute of Arctic Biology began analyzing the DNA of brown bears from around the world. Talbot, a graduate student, extracted DNA (deoxyribonucleic acid, the genetic information warehouse in the chromosomes of every living cell) from hundreds of Alaska brown bears. Starting with slivers of kidney or muscle tissue attained from hunting guides, Talbot used a process called polymerase chain reaction to copy tiny fragments of DNA millions of times.
When the DNA was in a readable form, Shields, a molecular evolutionary biologist, saw the DNA from brown bears on the ABC islands brown bears was unique when compared to brown bears anywhere else on the planet. Their closest relative is an unlikely one--the polar bear.
A polar bear's white coat, meat-only diet, and preference to live near and on sea ice make it hard to mistake for a brown bear. But Alaska's two largest bear species are closely related--so closely that brown and polar bears have mated in zoos and the union has resulted in fertile offspring. According to the Alaska Department of Fish and Game's "Wildlife Notebook Series," both types of bear had a common ancestor that was neither brown nor polar bear. As each adapted to different environments, the bears developed enough unique characteristics that they looked and acted like separate species.
With DNA evidence, Shields and his colleagues have launched a new hypothesis--brown bears may have appeared first; polar bears may have arisen from brown bears that wandered north and, over thousands of years, began to sprout white fur and teeth that were better for ripping apart seals than munching berries.
Shields and students Jackie Weicker and Scott Williamson are now working on a test that should tell them whether the polar bear sprung from brown bear lineage. When Shields and Talbot performed the initial study, they used bear DNA from cell mitochondria (energy-producing globules within a cell). In bears, however, as in people, mitochondrial DNA is passed from mother to baby, not father to baby.
Using mitochondrial DNA left the researchers with two possibilities--polar bears could have indeed evolved from brown bears, or a female brown bear may have at one time mated with a male polar bear. The result of that hybridization could have given the brown bears on the ABC islands their polar bear genes.
In the new study, the researchers will study cell nuclei DNA, which young animals inherit from both parents. If the nuclear DNA gives the same results as the mitochondrial DNA, it proves that the polar bear is indeed the ancient offspring of the brown bear. If not, the two species mingled at least once in their distant past, which would also explain the ABC islands bears' unique genetic fingerprint.
How can brown bears living 900 miles south of the nearest polar bear provide so much information about the origin of both species? In a paper written by Talbot, Shields and Timothy Heaton of the University of South Dakota, the authors claim polar bears could have evolved from a coastal form of brown bear in northeastern Siberia. These ancient brown bears may have migrated to Alaska about 40,000 years ago.
As time passed, the brown bear that spawned the polar bear died everywhere in Alaska but the ABC islands, which served as a refuge during the last glacial period. When the last ice age ended about 10,000 years ago, brown bears from farther south in North America slowly expanded their range to Alaska, but they neglected to swim the waters of the Inside Passage and mix with brown bears of the ABC islands. Good thing. Now we have a chance to find out whether polar bears owe their existence to brown bears.
Phylogeography of Brown Bears (Ursus arctos) of Alaska and Paraphyly within the Ursidae
Complete nucleotide sequences of the mitochondrial cytochrome b, tRNAproline, and tRNAthreoninegenes were described for 166 brown bears (Ursus arctos) from 10 geographic regions of Alaska to describe natural genetic variation, construct a molecular phylogeny, and evaluate classical taxonomies. DNA sequences of brown bears were compared to homologous sequences of the polar bear (maritimus) and of the sun bear (Helarctos malayanus), which was used as an outgroup. Parsimony and neighbor-joining methods each produced essentially identical phylogenetic trees that suggest two distinct clades of mtDNA for brown bears in Alaska: one composed only of bears that now reside on some of the islands of southeastern Alaska and the other which includes bears from all other regions of Alaska. The very close relationship of the polar bear to brown bears of the islands of southeastern Alaska as previously reported by us and the paraphyletic association of polar bears to brown bears reported by others have been reaffirmed with this much larger data set. A weak correlation is suggested between types of mtDNA and habitat preference by brown bears in Alaska. Our mtDNA data support some, but not all, of the currently designated subspecies of brown bears whose descriptions have been based essentially on morphology.
Gene flow between insular, coastal and interior populations of brown bears in Alaska
The brown bears of coastal Alaska have been recently regarded as comprising from one to three distinct genetic groups. We sampled brown bears from each of the regions for which hypotheses of genetic uniqueness have been made, including the bears of the Kodiak Archipelago and the bears of Admiralty, Baranof and Chichagof (ABC) Islands in southeast Alaska. These samples were analysed with a suite of nuclear microsatellite markers. The ‘big brown bears’ of coastal Alaska were found to be part of the continuous continental distribution of brown bears, and not genetically isolated from the physically smaller ‘grizzly bears’ of the interior. By contrast, Kodiak brown bears appear to have experienced little or no genetic exchange with continental populations in recent generations. The bears of the ABC Islands, which have previously been shown to undergo little or no female-mediated gene flow with mainland populations, were found not to be genetically isolated from mainland bears. The data from the four insular populations indicate that female and male dispersal can be reduced or eliminated by water barriers of 2–4 km and 7km in width, respectively.
Movement within Hood Bay was fairly limited, and for 19 established movements within the bay, the average was 3.1 miles. The longest movements were 7 miles by an adult boar and an adult sow.
Sex and Age Composition
The sex ratio of 44 bears captured was 48 males:100 females. The sex ratio of 18 bears under 3.5 years of age was 125 males:100 females while the ratio of tagged bears older than 3.5 years was 18 males:100 females. The sample size is small and the above figures are presented with the assumption that trapped bears were representative of the population. The ages used are from processed teeth but teeth from Southeastern bears are difficult to read and cannot be accurately read to the year. It is believed, however, that in most cases an age can be assigned which will be within one year of the true age.
Prior to September 1973 weights of captured bears were estimated while most of those caught in 1973 and 1974 were weighed using a 500-pound capacity Hanson Viking scale. The largest bear weighed was a 500 lb. 12.8-year-old sow. This bear was recaptured the following year, while accompanied by two 0.8-year-old cubs, and weighed 315 lbs. No adult boars were captured during the period when bears were weighed. Six sows between 9.8 and 15.8 years of age, all accompanied by cubs, averaged 319 lbs. The range was 250 to 390 lbs. Four cubs--of-the-year were weighed, one was a single female and weighed 95 lbs. while the other three were two males and one female from different sets of twins and weighed between 56 and. 70 lbs.