354
THE ESSEX NATURALIST
was seen most frequently among our catches on 2nd and 9th
October 1963 and 1964 and 69 of the 73 females exceeding 27 mm
carapace length collected on 6th November 1963 bore eggs. As
no females in our catch on 30th October carried eggs, egg laying
must have taken place between 30th October and 6th November
in 1963. These dates were confirmed in the October and Novem-
ber of 1964 suggesting that egg laying was confined to this period
for our population in the River Darent during both 1963 and 1964.
The smallest ovigerous females (27 mm carapace length) carried
an average of 70 eggs and the largest females (42 mm), 130 eggs.
Discussion
There are few published accounts of the bionomics of Euro-
pean crayfishes with which we can compare our observations.
Svardson (1949) noted that the females of Astacus astacus were
more common than males during late summer; his observations
were made on a Swedish lake population. Smolian (1925) noted
that the females of this species were dominant in July in German
rivers. Females of Austropotamobius pallipes outnumbered
males in June and July in the part of the River Darent studied by
us. Steffenberg (1872) noted that 'mature' females of Astacus
fluviatilis did not always carry eggs every year. In our popula-
tion 96% of 'mature' females (exceeding 27 mm carapace length)
bore eggs. Although we observed mating in a number of smaller
females none of these specimens were found bearing eggs. Bieber
(1940) observed copulation of Austropotamobius pallipes on 5th
November 1937 and of "Astacus fluviatilis" (probably Astacus
astacus) on 24th November, whilst de Bouville (1905) noted
mating in the latter on 25th January. Bieber (1940) reported
hatching of eggs of A. fluviatilis in June and July. In 1964 all
the observed matings in our River Darent specimens occurred
between 25th September and 30th October, while egg hatching,
from the 1963 mating, took place between 10-17th June 1964.
The distribution of Austropotamobius pallipes in the British Isles
There are few accounts, published before the last century, not-
ing the occurrence of the crayfish in counties of the British Isles.
In June 1668, Samuel Pepys made a passing reference to cray-
fishes with the remark "so come to Hungerford where very good
trout, eels, and crayfishes" (Warrington, 1958), and the crayfish
was noted in streams of Oxfordshire and Staffordshire by Plot (1677
1686). The stocking of pools and of rivers with crayfishes was,
apparently, a common practice in the past. For instance, in the
18th century Sir Christopher Medcalfe brought crayfishes from
southern England to Yorkshire and stocked the "pool Semur"
(arising from the River Baint) with them, where they apparently
bred (Sheppard, 1914). In 1922 large number of crayfishes were
introduced into the River Rye in Yorkshire (Smith 1932) and their
abundance in the rivers near Bingley and Gargrave almost caused