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Black Bear Science
Black bears on the Pacific Coast frequent
beaches, estuaries and streams where they live largely on
berries, intertidal invertebrates and fish. They hunt salmon
returning to spawning streams during the day and night and
take their prey into the forest to be eaten. Estimates put the
total weight of salmon transported into the forest by an
average bear at about 1600 kilograms. Bears prefer the eggs
and brains of salmon so that much of the carcass is left
uneaten to decay in the forest. The nitrogen released from the
decaying salmon carcasses is recycled back into the trees as
they grow. The decaying trees release the nitrogen into the
streams to be used by young salmon.
Two isotopes (or forms) of nitrogen are present
in nature – nitrogen 14 is mostly airborne and nitrogen 15
originates in the marine environment. Tom Reimchen from the
University of Victoria measured the nitrogen 14 and 15
isotopes ratios in augered cores from old trees in British
Columbia. His results showed a nitrogen 15 signal in tree
cores indicating a long period of a marine contribution to the
trees’ growth.
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