SEASONAL PATTERNS IN TRAP CATCHES OF THE CRAYFISH CAMBARUS-BARTONI AND ORCONECTES-VIRILIS IN 6 SOUTH-CENTRAL ONTARIO LAKES

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.