LIFE HISTORY OF ROBUSTUS GIRARD IN THE ERAMOSA-SPEED RIVER SYSTEM OF SOUTHWESTERN ONTARIO, CANADA (, ASTACIDEA)

BY

S. COREY Department of Zoology, College of Biological Sciences, University of Guelph, Guelph, Ontario, N1G 2W1, Canada

RÉSUMÉ La longévité moyenne de Cambarusrobustus est de 3 ans, avec très peu d'individus survivant une année de plus. Les animaux se reproduisent à la fin du troisième été. Les mâles de la forme I ont une longueur de carapace moyenne de 30,6 mm, S.D. 3,23 mm, et mesurent de 23,4 à 41,9 mm. Les femelles ovigères apparaissent à la fin de juin et en juillet. Les femelles à maturité ont une longueur de carapace moyenne de 29,7 mm, S.D. 1,42 mm, et mesurent de 24,3 à 34,3 mm. Le nombre moyen des oeufs est de 61,1 (S.D. 26,8). La taille, l'âge et la fécondité de C. robustusdans le système de rivières Eramosa-Speed sont bien inférieurs à ce qui a été observé dans la région des lacs Kawartha (Hamr & Berrill, 1985).

INTRODUCTION

Freshwater occur in large numbers, propagate rapidly, and are among the most energetically important benthic invertebrates feeding on detritus and, in turn are prey for many vertebrates (Crocker & Barr, 1968). The life histories are known for several species of Orconectes (which have been summarized and compared by Momot, 1984). The life histories of species of the genus Cambarus are not as well known. Only three species have been elucidated: Cambarus robustus Girard, 1852, C. bartonii (Fabricius, 1798) (by Hamr & Berrill, 1985) and Cambarus longulus longulus Girard, 1852 (by Smart, 1962). Cambarus robustus occurs in a broad band joining Georgian bay to the Niagara Peninsula and in Ontario it is confined to the Lake Huron, Lake Erie and Lake Ontario drainage basins. C. robustus also inhabits waters of New York, Pennsylvania, Ohio and West Virginia (Crocker & Barr, 1968). It is typically found in lakes and swift flowing rivers and streams invariably on stoney or rocky bottoms. Berrill (1978) found C. robustus to be uncommon but widely distributed in the Kawartha Lakes of Ontario. Neither Berrill (1978) nor Crocker & Barr (1968) detected a breeding season and felt that breeding was nonsynchronous and occurred year round. However further work by Hamr & Berrill (1985) showed that females were ovigerous in July with juveniles appearing in the population in late summer or fall. 226

From 1983 to 1986 many collections of C. robustus were made in the Eramosa and Speed rivers near Guelph. Many differences occurred between the life history of the Eramosa-Speed populations when compared to Hamr & Berrill (1985) findings.

MATERIALS AND METHODS

Specimens of Cambarus robustus were collected from three sites in southern Ontario: Eramosa and Speed Rivers near Guelph (43.5°N 80.5°W). All specimens were taken by hand and placed in 10% formalin. The stage of life cycle was determined for each as follows: juveniles; mature non- ovigerous females; mature ovigerous females; non-breeding males, form II; and breeding males, form I. The carapace length of each specimen was measured to the nearest 0.1 mm from the base of the eyestalk to the posterior edge of the carapace. Ten females (non-ovigerous) were selected each month (April through November), dissected with the state of maturity, and the diameter of the ova ( ± .02 mm) recorded. The fecundity, number of abdominal eggs carried per female, was determined.

RESULTS

Females became ovigerous at a mean CL of 29.7 ± 1.42 mm (n = 68) with a range of 24.3 to 34.3 mm. The mean CL of form I males was 30.63 ± 3.23 mm (n = 61) with a range of 23.4 to 41.9 mm. The ratio of Ct/ 9 varied from

Fig. 1. The diameter of ova in Cambarusrobustus Girard as compared to time of year.