Biology_of_Mustelids_Vol_1.pdf

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178.
is the final and evidently the most severe and dangerous stage of the disease
for the ermine, does not occur before the [spring at the] end of the next
hunting season after invasion by the larvae of Skr.1abingylus nasicola [in
the previous summer].
Ermines mate in the late spring or early summer, i.e. before the
skrjabingylosis infestation, and pregnancy lasts about ten months.
Consequently, if toxins from the parasitic worms influence the survival
rate of the embryos, the reduction in the size of the litter (and hence in
the numbers of the population as a whole) will also affect the pelt figures
only in the year following a heavy invasion.
Comparison betwean the changes in the pelt returns and the extent
of the invasion of the ermine in the hunting season shows that the fall in
the yield of pelts, reflecting a decline in the numbers of the animals,
does in fact occur in the year following a mass invasion of the population
by Skrjabingylus nasicola (Table 6).
The table shows that a definite relation exists between the yield
of pelts and the degree of infestation of the ermine population by Skr.1abin­
Qylus nasicola [in the previous year]
The years 1939-40 and 1940-41 in the Krasnoyarsk district are
exceptional.
Here, in 1939-40, the pelt figures dropped despite the fact
that the rate of skrjabingylosis infestation in the preceding year was
almost halved(a).
In 1939-40 the percentage of invaded ermines sharply
increased:
a reduction in numbers might have been expected in the
following year but this did not occur.
The discrepancy is evidently due to
the low infestation rate in the popUlation in 1939-40 (on average 3.8
parasites per ermine), and to improvement in food supplies.
'According to
correspondents the number of"miceH(b) and water rats increased in 1939.
(a) Presumably meaning, the rate for 1938-39 was half the rate for 1937-38,
but it is not according to Table 6, unless the figure 22.0, given by the
original text, was a misprint; or else Lavrov has made a logical error by
confusing the 50% difference between 1938-39 and 1939-40 with that between
1938-39 and 1937-38. - Ed.
(b) Small mouse-like rodents, including voles. - Ed.