出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/07/01 02:30:46」(JST)
| Kodiak bear | |
|---|---|
| A Kodiak Bear at Kodiak National Wildlife Refuge, Alaska, United States | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Family: | Ursidae |
| Genus: | Ursus |
| Species: | U. arctos |
| Subspecies: | U. a. middendorffi |
| Trinomial name | |
| Ursus arctos middendorffi Merriam, 1896 |
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| Kodiak bear range | |
The Kodiak bear (Ursus arctos middendorffi), also known as the Kodiak brown bear or the Alaskan grizzly bear,[1] inhabits the islands of the Kodiak Archipelago in the South West of Alaska. Its Alutiiq name is Taquka-aq.[2] It is by far the largest subspecies of brown bear and one of the two largest bears, the other being the polar bear.[3]
Taxonomist C.H. Merriam was first to recognize Kodiak bears as unique and he named the species "Ursus middendorffi" in honor of the celebrated Baltic naturalist Dr. A. Th. von Middendorff.[4] Subsequent taxonomic revisions merged most North American brown bears into a single subspecies (Ursus arctos horribilis), but Kodiak bears are still considered to be a unique subspecies (Ursus arctos middendorffi). Recent investigations of genetic samples from bears on Kodiak have shown that they are closely related to brown bears on the Alaska Peninsula and Kamchatka, Russia. It appears that Kodiak bears have been genetically isolated since at least the last ice age (10,000 to 12,000 years ago) and there is very little genetic diversity within the population.[5] Although the current population is healthy and productive, and has shown no overt adverse signs of inbreeding, it may be more susceptible to new diseases or parasites than other, more diverse brown bear populations.
Hair colors range from blonde to orange (typically females or bears from southern parts of the archipelago) to dark brown. Cubs often retain a white “natal ring” around their neck for the first couple years of life. The Kodiak's color is similar to that of their very close relative, the Grizzly bear.
Few Kodiak bears have been weighed in the wild, so some of the weights are estimates. Size range for females is from 225 kg (500 lbs) to 315 kg (700 lbs) and for males 360 kg (800 lbs) to 635 kg (1400 lbs).[2] Mature males average 480–533 kg (1,058–1,175 lb) over the course of the year,[6] and can weigh up to 680 kg (1500 lbs) at peak times.[2] Females are typically about 20% smaller and 30% lighter than males[2] and adult sizes are attained when bears are 6 years old. Bears weigh the least when they emerge from their dens in the spring, and can increase their weight by 20–30%[7] during late summer and fall. Bears in captivity can sometimes attain weights considerably greater than those of wild bears.
An average adult male measures 244 cm (8 ft 0 in) in length and stands 133 cm (4 ft 4 in) tall at the shoulder.[6] A wild male weighing 750 kg (1,650 lb) had a hindfoot measurement of 46 cm (18 in).[6] A large male Kodiak bear stands up to 1.5 m (5 ft) tall at the shoulder when it is standing on all four legs. When standing fully upright on its hind legs, a large male could reach a height of 3 m (10 ft).[2] The largest verified size for a captive Kodiak bear was for a specimen that lived at the Dakota Zoo in Bismarck, North Dakota. Nicknamed "Clyde", he weighed 966.9 kg (2,132 lb) when he died in June 1987 at the age of 22. According to zoo director Terry Lincoln, Clyde probably weighed close to 1,090 kg (2,400 lb) a year earlier. He still had a fat layer of 9 inches when he died.[8] A mass of 1,500 kg (3,300 lb) was published for this subspecies, but further details were not specified.[9]
They are the largest brown bear subspecies, and are comparable in size to polar bears. That makes Kodiak bears and polar bears both the two largest members of the bear family and the two largest extant terrestrial carnivores.[3]
The standard method of evaluating the size of bears is by measuring their skulls. Most North American hunting organizations and management agencies use calipers to measure the length of the skull (back of sagittal crest on the back of the skull to the front tooth) and the width (maximum width between the zygomatic arches — “cheek bones”). The total skull size is the sum of these two measurements. The largest bear ever killed in North America was from Kodiak Island with a total skull size of 78.1 cm (30.75 in), and 8 of the top 10 brown bears listed in the Boone and Crockett record book are from Kodiak.[10] The average skull size of Kodiak bears that were killed by hunters in the first five years of the 21st century was 63.8 cm (25.1 in) for boars and 55.4 cm (21.8 in) for sows.[11]
Although the term “Kodiak bear” is widely used to include all coastal Alaska brown bears, the subspecies only occurs on the islands of the Kodiak Archipelago (Kodiak, Afognak, Shuyak, Raspberry, Uganik, Sitkalidak, and adjacent islands). The Kodiak bear population was estimated to include 3,526 bears in 2005, yielding an estimated archipelago-wide population density of 0.7 bears/square mile (271.2 bears/1000 km²). During the past decade the population has been slowly increasing.[12]
Kodiak bears reach sexual maturity at age five, but most sows are over nine years old when they successfully wean their first litter. The average time between litters is four years. Sows continue to produce cubs throughout their lives but their productivity diminishes after they are 20 years old.[13] Mating season for Kodiak bears is during May and June. They are serially monogamous (having one partner at a time), staying together from two days to two weeks. As soon as the egg is fertilized and divides a few times, it enters a state of suspended animation until autumn when it finally implants on the uterine wall and begins to grow again. Cubs are born in the den during January or February.[2] Weighing less than a pound (<450 g) at birth with little hair and closed eyes, they suckle for several months, emerging from the den in May or June, weighing 15–20 pounds (7–9 kg).[2] Typical litter sizes on Kodiak are 2–3 cubs,[2] with a long-term average of 2.4 cubs per litter.[13] However, Kodiak bears have six functional nipples and litters of up to six cubs have been reported.[14] Sows are sometimes seen with five or six cubs in tow, probably due to adopting cubs from other litters.[2] Most cubs stay with their mothers for three years. Almost half of the cubs die before they leave,[13] with cannibalism by adult males being one of the major causes of death.
Kodiak bears that have recently left their mothers, at ages 3–5 years, have high mortality rates[2] with only 56 percent of males and 89 percent of females surviving.[12] Most young female bears stay within or near their mother’s home range, while most males move farther away. Most adult sows die of natural causes (56 percent), while most adult male bears are killed by hunters (91 percent).[12] The oldest known boar in the wild was 27 years old, and the oldest sow was 35 .[15]
Kodiak bears begin entering their dens in late October. Pregnant sows are usually the first to go to dens, males are the last. Males begin emerging from their dens in early April, while sows with new cubs may stay in dens until late June. Bears living on the north end of Kodiak Island tend to have longer denning periods than bears in the southern areas. Most Kodiak bears dig their dens in hill or mountain sides and they use a wide variety of denning habitats depending on which part of the archipelago they live on. Almost a quarter of the adult bears forgo denning, staying somewhat active throughout the winter.[2][12]
Bears on Kodiak are naturally diurnal (active during the day), but when faced with competition for food or space, they adopt a more nocturnal (active at night) lifestyle. This behavior is especially evident in the bears that live near and within Kodiak City. Kodiak bears do not defend territories, but they do have traditional areas that they use each year (home ranges). Because of the rich variety of foods available on Kodiak, the bears on the archipelago have some of the smallest home ranges of any brown bear populations in North America[16] and there is a great deal of overlap among the ranges of individual bears. Home ranges of adult sows on Kodiak Island average 50 sq mi (130 km2), while boar home ranges average 97 sq mi (250 km2).[12]
The islands of the Kodiak Archipelago have a subpolar oceanic climate with cool temperatures, overcast skies, fog, windy conditions and moderate to heavy precipitation throughout most of the year. Although the archipelago only covers about 5,000 sq mi (13,000 km2) there is a rich variety of topography and vegetation that ranges from dense forests of Sitka spruce on the northern islands, to steep glaciated mountains rising to Koniag Peak's 4,470 ft (1,360 m) along the central spine of Kodiak Island, to rolling hills and flat tundra on the south end of the archipelago. About 14,000 people live on the archipelago, primarily in and around Kodiak city and six outlying villages. Roads and other human alterations are generally limited to Afognak Island and the northeastern part of Kodiak Island. About half of the archipelago is included in the Kodiak National Wildlife Refuge.[12]
Bears live throughout the archipelago, adapting to local resources and retaining relatively small home ranges and comparable densities in most habitats. Emerging vegetation and animals that died during the winter are the first foods bears eat in the spring. As summer progresses, a wide variety of vegetation supplies nutritional needs until salmon return. Salmon runs extend from May through September on most of the archipelago and bears consume the five species of Pacific salmon that spawn in local streams and lakes. In the late summer and early fall, bears consume several types of berries. Bears also feed on wind-rowed seaweed and invertebrates on some beaches throughout the year. Although deer are abundant on the archipelago and mountain goats are abundant on Kodiak Island, few Kodiak bears actively prey on them. Another food source available year round is the abundant garbage supplied by the human population of Kodiak Island. [12]
There have been no scientific studies evaluating the senses or intelligence of Kodiak bears. Subjective observations and comparisons to other bears suggest that Kodiak bears have eyesight that is comparable to humans (they are not “near sighted”), have hearing that is comparable to an average dog, and have a sense of smell that is up to four times more acute than the average dog. Their level of intelligence seems to be somewhere between that of an average canine and a primate. Due to their level of intelligence, individual bears have personalities and unique ways of dealing with situations.[17]
Kodiak bears are generally solitary in nature; however, when food is concentrated in small areas, such as along salmon spawning streams, grass/sedge flats, berry patches, a dead whale, or even an open garbage dump they often occur in large groups. Along a few drainages on Kodiak, up to 60 bears can be seen simultaneously in a square mile area (2.6 km2). To maximize food intake at these important areas, bears have learned to minimize fighting and fatal interactions by developing a complex communication (both verbal and body posturing) and social structure.[17]
In most circumstances, Kodiak bears keep away and attempt to avoid encounters with people. The most notable exceptions to this behavior pattern occur when bears are surprised, threatened, or attracted by human food, garbage, or hunter-killed game. Bear safety precautions center around avoiding such situations, understanding bear needs and behavior, and learning how to recognize the warning signs bears give when stressed.[18][19]
The most recent occurrence of a fatal bear attack on a person on the Kodiak archipelago was in 1999.[20] The National Geographic Society filmed a television program about two brown bear attacks. A fatal attack occurred on Uganik Island (November 3rd, 1999), part of the Kodiak archipelago; the other attack occurred on Raspberry Island, home to two full-service wilderness lodges. Both hunters were returning to game they had killed previously and left alone to go kill another. One of the hunters was killed by the bear and the other, after being attacked, stabbed the bear with a knife, then recovered his rifle and killed the attacking bear. Prior to that, the last fatality was in 1921.[21] Both incidents involved hunters that were hunting by themselves. About once every other year a bear injures a person on Kodiak.[22]
Early human occupants of the archipelago looked to the sea for their sustenance. At that time, Kodiak Natives (Alutiiqs) occasionally hunted bears, using their meat for food, hides for clothing and bedding, and teeth for adornment. Traditional stories often revolved around the similarity between bears and humans, and around the mystical nature of bears because of their proximity to the spirit world.[23]
Russian entrepreneurs came to the area in the late 18th century to capitalize on the abundant fur resources. Bear hides were considered a “minor fur” and sold for about the same price as river otter pelts. The number of bears harvested increased substantially when sea otter populations declined and after the United States acquired Alaska in 1867, bear harvests on Kodiak increased, peaking at as many as 250 bears per year. Commercial fishing activities increased in the late 1880s and canneries proliferated throughout the archipelago. Bears were viewed as competitors for the salmon resource and were routinely shot when seen on streams or coasts. At the same time, sportsmen and scientists had recognized the Kodiak bear as the largest in the world, and they voiced concerns about overharvesting the population.[21]
Professional interest in guided Kodiak bear hunts and a concern for unregulated resource use in frontier lands such as Alaska prompted the territorial government’s newly established Alaska Game Commission to abolish commercial bear hunting (selling the hides) on the archipelago in 1925. The impacts of the new regulations seemed to restore bear populations on the Kodiak islands. By the 1930s, ranchers on northeast Kodiak reported an increase in bear problems and demanded action. Bears were also seen as a threat to the expanding commercial salmon fishing industry. To address the dilemma of conserving bears while protecting cattle, salmon and people, President Franklin D. Roosevelt created the Kodiak National Wildlife Refuge by Executive Order in 1941.[23] The 1,900,000-acre (7,700 km2) refuge roughly encompasses the southwestern two-thirds of Kodiak Island, Uganik Island, the Red Peaks area on northwestern Afognak Island, and all of Ban Island.
Alaska achieved statehood in 1959 and assumed responsibility for managing the state’s wildlife. The Alaska Board of Game reduced bear-hunting seasons on Afognak and Raspberry islands and on the Kodiak National Wildlife Refuge, but liberalized bear seasons on non-refuge lands on Kodiak. During the 1960s, state biologists worked with ranchers along the Kodiak road system to examine and reduce the predation problem. Biologists reported that cattle and bears were not compatible on the same ranges and potential solutions included poisons, fences to isolate cattle ranges, and aerial shooting of bears. Again, sport hunters voiced their support for Kodiak bears. In spite of public pressure, the state continued actively pursuing and dispatching problem bears until 1970.[24]
In 1971, the Alaska Native Claims Settlement Act (ANCSA) resolved many long-standing land issues with aboriginal Alaskans statewide. The impacts were felt strongly on the archipelago as large areas were conveyed to the Native corporations. Federal management of the National Forest lands on Afognak was transferred to Native Corporation ownership with passage of the Alaska National Interest Lands Conservation Act (ANILCA) in 1980, and the Kodiak National Wildlife Refuge lost control of 310,000 acres (1,300 km2) of prime bear habitat (more than 17 percent of refuge lands).[23]
In 1975, construction of a logging road began on Afognak Island, and timber harvesting began in 1977. In 1979, work began on an environmental impact statement for the Terror Lake hydroelectric project on Kodiak Island. That project included an earthen dam on Terror Lake with Kodiak National Wildlife Refuge and a 6-mile (9.7 km)–long tunnel through a mountain ridge to a penstock and powerhouse in the Kizhuyak River drainage. The hydro project was the first significant invasion of inland bear habitat on Kodiak Island. To address the opposition encountered from the public and agencies, a mitigation settlement was negotiated in 1981 which included brown bear research and establishment of the Kodiak Brown Bear Trust.[25] The hydroelectric project was completed in 1985. Human alteration of bear habitat on Kodiak and Afognak islands spurred renewed interest and funding for bear research on the archipelago, resulting in a surge of baseline and applied bear research on Kodiak through the 1980s and 1990s.
Bears were not directly harmed by the Exxon Valdez oil spill in 1989, although some were displaced from traditional feeding and traveling areas by cleanup crews. No one was injured by a bear, and no Kodiak bears were killed. To mitigate the adverse impacts of the spill, Exxon reached a settlement with the state and federal governments. Paradoxically, the impacts of the oil spill and the subsequent cleanup and settlement proved to be beneficial to bears on Kodiak. Bear-safety training exposed thousands of workers to factual information about bears, and money from the settlement fund was used for funding land acquisitions. By the close of the 20th century, over 80 percent of the refuge lands that had been lost as a result of ANCSA and ANILCA were reinstated into the refuge, either through direct purchase or by means of conservation easements. Lands were also purchased in America, Westtown, and Shuyak islands and transferred into state ownership. The Kodiak Brown Bear Trust coordinated a coalition of sportsmen and other wildlife conservation groups from around the nation to lobby for use of settlement funds to acquire Kodiak lands. The groups also directly contributed funding to protect small parcels of important bear habitat around the islands.[23]
In 2001, a Citizens Advisory Committee was established to work closely with the Alaska Department of Fish and Game, with the cooperation of Kodiak NWR, to develop a management plan addressing several problems that affect bears, including hunting, habitat, and viewing. The resulting Kodiak Archipelago Bear Conservation and Management Plan[26] was crafted over several months by representatives from 12 diverse user groups, which, after hearing from a variety of experts from agencies and receiving extensive public input, developed more than 270 recommendations for managing and conserving Kodiak bears. Despite the diversity of viewpoints expressed by members of the group, all of the recommendations were by consensus .
The underlying themes of the recommendations were continued conservation of the bear population at its current level, increased education programs to teach people how to live with bears on Kodiak, and protection of bear habitat with allowances for continued human use of the Archipelago. Although the group's role is merely advisory, government management agencies expressed a commitment to implement all of the regulations that were feasible and within their legal jurisdictions.
The International Union for Conservation of Nature red list does not list subspecies. The brown bear species, of which the Kodiak subspecies is a member, is listed as LR/lc (Lower Risk Least Concern).[27] The Kodiak is not listed as an endangered species by the endangered species program of the U.S. Fish and Wildlife service.[28]
Kodiak bear research and habitat protection is done cooperatively by the Alaska Department of Fish and Game and Kodiak National Wildlife Refuge. Bear hunting is managed by the Alaska Department of Fish and Game and hunting regulations are established by the Alaska Board of Game. There is currently a finely-tuned management system that distributes hunters in 32 different areas during two seasons (spring: April 1 – May 15, and fall: October 25 – November 30). Each year about 4,500 people apply for the 496 permits offered for Kodiak bear hunts (two-thirds to Alaska residents, one-third to nonresidents). Nonresidents are required to hire a registered guide who is authorized to hunt in a particular area, and this can cost from $10,000–$22,000. All hunters must come into the Alaska Department of Fish and Game (ADF&G) office in Kodiak prior to going into the field for a brief orientation and must check out before they leave the island. Every bear that is legally killed on the Archipelago must be inspected by an Alaska Department of Fish and Game wildlife biologist before it can be taken from the islands.[29] Pelts receive a stamp from an ADF&G officer if the hunter and guide provide proper documentation to prove licensing. Pelts can not be transported or legally preserved or sold without the official stamp. Hunting laws are strictly enforced by both the ADF&G officers who often have the full support of the local community. Illegal hunting and fishing is frowned upon by the community which maintains a healthy respect for the island's environmental laws as well. Stiff penalties accompany illegal hunting and fishing. The island's remote location makes trafficking in illegal pelts difficult for would-be poachers.
Since statehood, the reported number of Kodiak bears killed by hunters has ranged from 77 (1968–69) to 206 (1965–66). From 2000–2006, an average of 173 Kodiak bears were killed by hunters each year (118 during the fall season and 55 in the spring season). Over 75 percent of those were males. An additional nine bears were reported killed annually in defense of life or property during the same time period. There has been an increasing number and percentage of large, trophy-sized bears (total skull size at least 28”) killed by hunters in recent years. In the 1970s, only 2.5 percent of the bears killed on Kodiak were trophy-sized; in the 1990s and 2000s the proportion increased to almost 9 percent.[11]
In the past 20 years, bear viewing has become increasingly popular on Kodiak and other parts of Alaska. The most accessible bear viewing location on Kodiak, Frazer River, had over 1,100 people come in 2007. Visitor numbers have been increasing at about 10 percent annually and there are plans for development of additional bear viewing areas on Kodiak. There are also other bear viewing opportunities through air-taxi, charter boat, remote lodge and trekking operations on the Archipelago.
Although bear viewing is often considered a “non-consumptive” use, it can have serious impacts on bear populations if it is not conducted properly. Most viewing occurs at places where bears congregate because of feeding opportunities that are critical to their survival. If some bears avoid these areas because people are there, those bears may not get the fat and protein they need to make it through the upcoming winter. Consequently un-managed bear viewing could impact several bears, especially productive sows with cubs.
Often bear viewing and bear hunting are considered incompatible. Even if the bear population is healthy and bear hunting is sustainable, ethical questions arise especially if hunting occurs near viewing areas and either during or soon after the viewing season. Many feel that it is not fair to encourage bears to be close to people during the summer only to allow them to be shot in the fall. The Kodiak bear plan recognized bear hunting as a legitimate, traditional, and biologically justifiable activity. It recommended that agencies find ways to make bear hunting and bear viewing compatible on the Archipelago.[26]
Appearance. The polar bear is the largest member of the bear family, with the exception of the Alaska’s Kodiak brown bears, which equal polar bears in size.(Overview page)
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