The black-footed ferret once ranged across most of the central plains of North America
from southern Canada to Texas. Its lifestyle is closely linked to that of the prairie
dog (Cynomys leucurus), a squirrel-like rodent that lived in huge colonies on the plains.
The ferret feeds mainly on prairie dogs but can feed also on mice, ground squirrels,
and rabbits. However, 90% of its diet comprises prairie dogs. The ferret lives in the
warrens or burrow systems of the prairie dogs and hence that species provided
the ferret with both its habitat and a large proportion of its food supply. Around
the turn of the century there was a concerted effort to eradicate the prairie dog,
which was viewed as vermin by ranchers. It was seen as competing with sheep
and cattle for grass and its burrow systems made riding a horse most unsafe. The
prairie dogs were poisoned, trapped, and shot in their millions by farmers and by
government pest controllers. As the prairie dogs went, so did the ferrets. By the
middle of the century they were judged to be extinct, but in 1964 a small popula-
tion was discovered in South Dakota. That colony died out in 1973. In 1981 a colony
was discovered in Wyoming. Careful censusing produced an estimate of 129
individuals in 1984, but by the middle of 1985 the population had declined to
58 animals and within a few months was down to 31. Canine distemper was
diagnosed in this population and it might well have been the cause of that decline
(see Section 11.11.3).
With the population obviously threatened there was an attempt to capture the re-
maining animals to add to an already established captive breeding colony. Five were
caught in 1985, 12 in 1986, and one in 1987. By February 1987 the last known
wild black-footed ferret was in captivity. Captive breeding was successful, and 49
and 37 ferrets were released in 1991 and 1992 into their former range in Wyoming
(Biggins et al. 1999).The type example of serious declines caused by hunting is provided by the history
of commercial whaling. It demonstrates the effect of the discount rate (see Section
19.8) upon the commercial decision determining whether a sustained yield is taken
or whether the stock is driven to commercial extinction.
Market economics will act to conserve a commercially harvested species only when
that species has an intrinsic rate of increase rm(see Section 6.2.1) considerably in
excess of the commercial discount rate, the interest a bank charges on a loan to a
valued customer. Hence, when a species is harvested commercially, the yield must
be regulated by an organization whose existence and funding is independent of the
economics of the industry that it regulates; otherwise it will necessarily endorse the
quite rational economic decisions of the industry, which may well be to drive a stock
to very low numbers and then to switch to another stock.The muskoxen in mainland Canada
Unregulated commercial hunting reduced the muskoxen (Ovibos moschatus) on the
arctic mainland of Canada to about 500 animals by 1917. In that year the species
was protected by the Canadian government. The size of the historic populations will
never be known but, ironically, documentation of the purchase of the muskox hides
from native hunters by the trading companies was detailed. Barr (1991) collated the
records and estimated that a minimum of 21,000 muskoxen were taken between 1860
and 1916. Their hides were shipped to Europe as sleigh and carriage robes, replacing
bison robes after that species had been reduced almost to extinction.CONSERVATION IN PRACTICE 317
18.2.5The effect of
poorly regulated
commercial hunting