SEASONAL MIGRATIONS AND REPRODUCTIVE PATTERNS IN THE LAKE STURGEON, ACIPENSER-FULVESCENS, IN THE VICINITY OF HYDROELECTRIC STATIONS IN NORTHERN ONTARIO

This study was conducted in order to evaluate seasonal migratory behav iour and reproductive pattern of lake sturgeon in a confined region of the Mattagami River system in northern Ontario where river flow is re gulated by hydroelectric works. Radio tracking and the systematic samp ling of lake sturgeon using gill nets indicated that the distribution of fish throughout the study site varied on a seasonal basis. This dis tribution was related to the migration of individuals to potential spa wning sites in the spring, a post-spawning dispersal to feeding areas and late summer migration to an area of concentration on the Groundhog River which is a tributary of the Mattagami River. There was a high p roportion of fish (about 50%), within the size range of reproductively active fish, found in the vicinity of suitable spawning habitat durin g early May. Measurement of the gonadosomatic index (GSI) and plasma s ex steroid hormone levels revealed a divergent pattern of reproductive development between the sexes. Female sturgeon exhibited a prolonged period of ovarian regression following spawning. Resumption of ovarian development was not evident until September and was characterized by an increased GSI and plasma levels of testosterone and 17 beta-estradi ol. In contrast, male lake sturgeon began testicular recrudescence wit hin one month of spawning with the GSI reaching prespawning levels by September; reproductive hormones were at prespawning levels by the end of June. It seems that hydroelectric works has complex effects on stu rgeon in the Mattagami system. The extensive migratory behaviour of la ke sturgeon within the study area make it prone to impingement or entr ainment whereas the altered river now appears to enhance reproductive development.