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Human Disturbance
Ecotourism accounts for a large proportion of economic income in many
wilderness areas, including Alaska. Fishing, bear viewing, and hunting draws
millions of people to Alaska each year. Historically, it is believed that brown and
black bears either become habituated to human presence or are displaced by
ecotourism. Despite the effects of human disturbance on wildlife, there has not been
a study regarding the effects on brown and black bears in Alaska. At Glacier Creek, Kenai Peninsula, Alaska, there is an
undisturbed population of brown and black bears. At this site, preliminary results
from a disturbance study showed that brown bears, collared with GPS units to track their
locations, avoid the section of the creek while humans are present and for a few weeks
afterward. With controlled ecotourism, it is unknown what effect human disturbance
will have on behavior, however if bears avoid human presence, they will be detrimentally
affected nutritionally.
Possible detrimental effects of ecotourism on bear nutrition are as
follows: a decrease in the amount of time spent by bears on salmon streams, a decrease in
salmon availability, a possible decrease in overall dietary meat intake and an increase in
time spent foraging for berries. To gain the necessary protein and energy by feeding
only on berries, the time and energy spent foraging would have to increase. Due top
the social hierarchy of bears, if larger brown bears are increasing their time foraging
for berries this could displace black bears and sub adult brown bears from that food
resource. On the other hand, if bears become habituated and lose their fear of
humans, then the chances of bear-human interactions increase. Regardless, people
will need to be taught the proper methods of food storage, especially salmon they catch,
to minimize risk to both humans and bears.
Nutritional Value of Food Resources
Brown and black bears vary their diets seasonally. Upon emergence from
hibernation, bears usually feed upon forbs and any terrestrial meat available. Forbs
are broad-leaved herbs other than grasses and are chosen over grasses because they are a
more digestible protein source. Upon arrival of salmon and production of berries in
the summer and fall months, bears turn to these sources to meet their nutritional needs
and gain body mass.
When salmon and berries are available, salmon is eaten
preferentially by brown bears because salmon contain high amounts of protein.
Berries are utilized more often and earlier in the season by black bears for two
reasons. First, black bears are smaller than brown bears; therefore they are more
able to meet their energetic needs consuming berries. Second, black bears are
excluded at salmon streams by brown bears. Berries contain from 3-7 % protein while
salmon has about 69%, based on dried samples. For spawning sockeye salmon, the
protein, fat, and energy levels are higher in the reproductive organs than in the rest of
the bodily tissue and higher in females than males. This supports the idea that
brown bears preferentially consume females that have not yet spawned for the roe because
of the higher fat, energy, and protein content.
The mixing of diets by brown bears results in different
gains in body composition. Diets containing high-protein contents primarily lead to
a gain in lean body mass, which is important in replacing weight lost during
hibernation. A low-protein, high-energy diet primarily results in fat gain. As
salmon becomes available in the summer months, bears move to this high-protein food
source. Later in the summer, as berries become available, bears incorporate both
food sources into their diet. Diet mixing occurs seasonally in most wild bear
populations. One explanation for this may be that the maintenance energy cost for
brown bears varies with the level of dietary protein, with minimal costs ranging from
20-40% dietary protein.
Learning of Diet Mixing
Social Learning
As has been shown in most mammals, brown and
black bear cubs learn what food sources to use and how to use them primarily from their
mothers and secondarily from peers. For the first two to three years of a bear's
life cubs follow their mother while she forages and fishes for salmon, imitating her and
consuming what she chooses. During these initial years, bears learn to feed on
salmon, terrestrial meat, forbs, and berries.
After the initial years with the sow, subadult
bears, three to five years of age, often travel in small groups. During this period
they have many new experiences, trying to learn where they fit into the social system, and
learn from their peers. Subadults play with each other, learning how to fight, which
is vital for survival. As they age and approach sexual maturity, bears become
solitary with the exception of breeding season.
Individual Learning
After brown and black bears are full-grown they
are primarily solitary, continuing to learn from individual experience. Males wander
until they are large enough to establish their own territory, normally encompassing female
territories, in order to breed. During this time, male brown bears learn to avoid
dominant males to survive. Adult male and female black bears learn to avoid food
sources that are occupied by brown bears, therefore, black bears often only use salmon
streams when brown bears are absent.
Innate
Although food abundance and social structure
determines a large part of what a food is available to bears, they also make decisions
based on the innate ability to determine nutritional value. Animals receive positive
or negative feedback after consuming a food resource that leads to preferences and
aversions. The positive feedback brown bears receive may vary with the time of year
and the type of body mass gain needed. Brown bears need to add lean body mass when
they are growing and upon emergence from hibernation in the spring. Fat gain is
important in the fall period of hyperphagia, a period of increased food intake, for
survival through hibernation, especially for a female to support cubs.
Conclusion
Habituation of bears to humans on salmon streams can increase the number of
bear-human interactions. If anglers are irresponsible by fishing to close to bears
or are not storing their catches properly, bears will learn to associate humans with
salmon. The association of food with humans is a main cause of damage to life and
property by bears, which ultimately leads to bear fatalities. Ecotourism needs to be
properly managed with education for human users, to prevent unnecessary conflict.
Management often involves limitations of fishing locations to avoid prime areas of bear
use and proper regulations for bear encounters. Regulations may include not fishing
within a predefined distance of a bear, cutting the fishing line if a bear approaches a
hooked salmon, and storing any food in bear proof containers. All of these
approaches improve the safety of both humans and bears.
Avoidance can be a larger concern than
habituation because it may decrease the dietary nutrition of bears. Studies need to
take place to see if avoidance is occurring or if bears will adjust to human
presence. If bears will not fish where humans are located then it is important to
limit the time that humans spend on the salmon stream. In Alaska, where it is light
almost 24 hours a day in the summer, people tend to fish at all hours. Bears must be
given a certain amount of light with no human presence so that they can catch enough fish
to sustain themselves.
Literature Cited
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Transcript 59 North American Wildlife and NR Conference
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