Studies and Decline in Porcupine Caribou Herd
Alaskan wildlife biologist Dr. Stephen M. Arthur sheds some light
on population changes in the herd in recent times. Here are some of his
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"There are several factors that may be involved in the decline of the Porcupine
Caribou Herd (PCH) during the mid to late 1990s.
Alaska Department of Fish and Game
Increase in Mortality of Adults: The most likely explanation is that
there has been an increase in mortality of adults compared to the 1980s when
the herd was increasing. There are several possible causes of this, but we
don't have enough information to say which ones are the most important.
Mid Winter Weather: Severe mid-winter weather the
past two winters may be one of the factors leading to the
herd's population decline, although we have not seen a reduction
in body condition of cows during mid-winter, which would
be expected if winter weather were reducing survival.
Predators: Predator populations in the summer and
winter ranges seem to be fairly high, and we have had many
reports of wolves preying on caribou on their winter range.
Moose Population/Wolves: Also, the moose population
(which would be the primary alternate prey for wolves) in
much of the herd's summer range has declined dramatically
since the 1980s, so wolves in this region must have increased
their reliance on caribou.
Human Harvest: Meanwhile, the human harvest of Porcupine
caribou, which occurs mainly on the winter range and during
migration, has not declined and may have increased slightly.
...Or is this part of a Natural Cycle?
may be part of a natural cycle where a period of increase is followed by
a period of decrease. Most arctic caribou herds
periods of several decades. We haven't been studying this herd long enough
to understand how the different pieces of the puzzle fit together. So, my best
guess is that there has been a combination of things that increased adult