A project involving bear hunters, antibiotics and barbed wire has provided revealing insights into one of the world's densest populations of black bears, on Kuiu Island in Southeast Alaska.
Bear researcher Lily Peacock found that Kuiu Island, about 40 miles west of Petersburg, has three to five bears per square mile. Peacock also found that surprisingly high numbers of bears coexist seasonally on salmon streams on the island. She counted 115 different bears using a one-mile stretch of stream during a two-month period.
"Using modeling techniques that look at patterns of capture and recapture, we estimated about 175 bears used that segment of that stream over two months," Peacock said. "That surprised me. It was corroborated with other work that I did, observing bears from tree stands."
Peacock said it's difficult for an observer to keep track of that many different bears. A casual observer might see 20 bears, she said, but you don't know if that's seeing five bears four times or 20 different bears. To identify individual animals, she used the same genetics techniques forensics experts use on crime scenes, extracting DNA from hair follicles. Peacock collected 1,554 hair samples from trails along seven streams in 2000 and 2002.
"I put hair snares on salmon streams," she said. "They're not fancy, just a single strand of barbed wire I strung between trees. The bears walk under them and left hair, and I was able to extract DNA from the hair and get a genetic fingerprint. So I was able to say, 'Bear A, bear B, bear C and bear D, all came under this fence this week.' Then I would come back the next week and I could say, 'There's bear A again, and bear F and bear Z.'"
The Alaska Department of Fish and Game and the U.S. Forest Service's Petersburg Ranger District worked with Peacock on the four-year project, which was part of her Ph.D. dissertation at the University of Nevada, Reno. Wildlife biologist Kim Titus, now Deputy Director for the Division of Wildlife Conservation, served as Peacock's Alaska adviser.
Titus said Fish and Game provided the primary funding for the research, and initiated the project because of concerns about the high hunter harvest of Kuiu Island black bears.
The island is renowned among bear hunters, Titus said, and the big game guiding industry shared wildlife managers concerns about the island's bears. The cooperation of guides and hunters was instrumental in the success of the project.
"We had tremendous support and interest from Petersburg Ranger District - Tongass National Forest staff," Titus said.
"The project really paid off," he said. Fish and Game uses the information to set harvest levels and the Forest Service issues permits to guides."
Peacock and Titus said there is not much research on black bears in Southeast Alaska, or on how black bears use salmon streams.
"We all know black bears use salmon on Anan Creek," she said, "but other than these prize fishing spots, we wanted to know how black bears use the run-of-the-mill salmon streams, of which there are thousands up and down Southeast Alaska, the streams that are the backbone of the forest. And one thing this project did was to demonstrate how many black bears use these streams."
Peacock was surprised by some of the differences in behavior between black and brown bears. Bears deal with the safety of their cubs in different ways, she said. Brown bear mothers keep their cubs close at hand, while black bears often leave their cubs while they fish, usually sending them up a tree.
Despite the high numbers of bears on the streams, Peacock rarely saw bears fight. She said the bears practice sexual segregation, with males and females fishing at different times, and the average stay on a stream for a bear was two weeks. She said that although bears are solitary animals for the most part, they are forced to be together on the salmon streams, and they've developed mechanisms to work together in these seasonal high densities.
"They keep their distance from each other," she said. "With this huge density you'd expect more conflict, but there wasn't. They avoid each other. Brown bears up north can be pretty scarred up from fights. But not these bears. They look beautiful."
Titus said the super abundance of food helps relieve a lot of the potential stress in the population.
Peacock worked with hunters to estimate the total number of black bears on Kuiu Island. She used a standard technique called mark-recapture.
Tetracycline, a commonly administered antibiotic, was used to mark the bears. When tetracycline is ingested by a bear or a human, it leaves a mark on bones and teeth. The mark is visible when a cross section of bone is seen under a microscope with ultraviolet light.
"Our bones and teeth are constantly growing and remodeling. New material is being absorbed and created every day," Peacock said. "If a bear eats tetracycline, a tiny layer appears. Capturing bears is expensive, so we let the bears mark themselves."
Peacock designed bait stations that minimized chances of animals other than bears taking tetracycline-laced bait. In June of 2000, about 200 stations were set up along roads and beaches in the area that connects northern and southern Kuiu Island, and about 130 bears were marked. In 2002, 263 bait stations were established, one on every square mile of the island, and about 195 bears were marked. The number of bears marked was based on the number of baits consumed by bears.
Bear hunters were asked to submit toe bones from bears they killed, and that provided the "recapture" data. Titus said cooperation from hunters was almost 100 percent.
Of 166 bears harvested on Kuiu during the 2000-2001 hunting season, 11 (6.6 percent) were found to be tetracycline-marked. Overall, Peacock found 32 marks in 503 samples taken from Kuiu and nearby Kupreanof Island. Peacock estimated the population of black bears on Northern Kuiu Island to be 1,019, and the overall density to be about four bears per square mile. The results were consistent for both rounds of the study.
"It's a snapshot in time," she said. "You need several estimates to determine trends, whether the population is stable, increasing or decreasing."
Titus said Fish and Game will continue to refine the population estimate with additional samples from bear hunters. The tetracycline mark will stay in the bones of marked bears for four years. Hunters have harvested black bears on Kupreanof Island that were marked on Kuiu, so fish and game is requesting toe bones from all black bears taken on both Kupreanof and Kuiu islands. This will allow wildlife managers to evaluate the extent to which bears are moving back and forth between the two islands.
"By combining new and innovative DNA methods in wildlife and conservation genetics to solve some old-fashioned wildlife management problems of estimating bear numbers, we are collectively able better manage black bears for long-term sustainability," Titus said.