DISTRIBUTION OF THE CRAYFISH IN BRITISH ISLES 353
During September we recorded the largest number of cray-
fishes in our section during the period of study. This September
catch included crayfishes hatched in June 1964 as many of these
had now reached a carapace length of 10 mm by late September
they could be sexed. October saw a sharp decline in catch num-
bers and a noticeable absence of ovigerous females that were
again to be found in the deeper waters beyond our section. Our
October catch however, contained a greater proportion of juve-
nile females than either juvenile or adult males.
The growth of crayfishes less than 10 mm carapace length.
In our catches for May 1964 the smallest specimens present
measured 12-13 mm carapace length. That these represented the
1963 hatchlings is based on the following observations made
from June to October in 1964 on the growth of hatchlings for
that year.
Ovigerous females, exceeding 27 mm carapace length, cap-
tured on June 10th, 1964 bore eggs in an advance stages of
development. In the catches of June 17th, no egg bearing fe-
males were present but most females exceeding 27 mm had
hatchlings attached to their swimmerets. Our catch on June
24th contained large numbers of these juveniles measuring 5-6
mm carapace length, and throughout July we caught numerous
juveniles measuring 7-8 mm carapace length; in August young
of 8-9 mm carapace length were abundant. By the last week in
September this juvenile population had reached 10-11 mm cara-
pace length. It was now possible to determine their sex and they
were included in the total of our September catch.
By October 1964 these crayfishes measured 12-13 mm carapace
length. Thus, the juveniles of that size caught from October 1963
until May 1964 must have been hatched in June of 1963. Their
growth had apparently ceased in October and was resumed in the
May of 1964 when we first observed moulted specimens in our
population.
Newly moulted crayfishes first appeared in our catches on 16th
May, and in 1964 moulting also commenced between 10th-16th
May.
Mating behaviour
Copulation was first observed during the last week of Septem-
ber for the years 1963 and 1964, specimens of both sexes
exceeding 22 mm carapace length. Specimens held in temporary
captivity during our collecting periods on 2nd, 9th and 16th of
October 1963 and 1964, were also seen to mate. Males of 23-55
mm carapace length were the most active participants. The
smallest female that received spermatophores from the males
measured 23 mm carapace length. Mating lasted from 2-25
minutes and only those females held by males for periods longer
than 10 minutes were seen later to bear spermatophores. Mating