Km. Somers et Rh. Green, SEASONAL PATTERNS IN TRAP CATCHES OF THE CRAYFISH CAMBARUS-BARTONI AND ORCONECTES-VIRILIS IN 6 SOUTH-CENTRAL ONTARIO LAKES, Canadian journal of zoology, 71(6), 1993, pp. 1136-1145
Crayfish were trapped in six south-central Ontario lakes to examine se
asonal changes in estimates of relative abundance Baited-trap catches
of Cambarus bartoni and Orconectes virilis correlated with changes in
water temperature. Cambarid catches increased in the spring until a mi
dsummer maximum, but dropped suddenly as the water temperature began t
o fall in August. Ovigerous (i.e., egg-bearing) females and recently m
oulted males were captured by SCUBA divers in August. Trap catches inc
reased, once breeding and moulting periods concluded, and subsequently
decreased as water temperatures continued to drop in the autumn. In c
ontrast, catches of male O. virilis increased in the spring and remain
ed relatively constant throughout die summer until water temperatures
fell in September. Catches of female O. virilis peaked somewhat later
in the summer and then gradually declined in the early fall. Although
the two species and the two sexes differed in the length of the midsum
mer sampling period when trap catches were relatively constant, simila
r seasonal trends among lakes suggest that midsummer trap catches can
be used to estimate crayfish relative abundance. Other factors, such a
s the presence of smallmouth bass (Micropterus dolomieui), lake physic
al and chemical characteristics, and the number of co-occurring crayfi
sh species also correlated with trap catches. Both the presence of bas
s and the number of co-occurring species of crayfish probably affect c
rayfish behaviour and activity, thereby reducing catches in baited tra
ps, but not necessarily affecting actual population abundance. Compari
sons of relative abundance based on catches from baited traps must con
trol for these seasonal behavioural, and environmental factors.