Post-Impoundment Changes to the Speed River Fish Assemblage

Abstract

Changes to the Speed River fish assemblage were investigated 27 years after the creation of the Guelph Lake reservoir. Electro-fishing and seine haul data collected during 2003 were compared to pre- (1975) and post-impoundment (1976 and 1978) surveys. Since its creation, the Guelph Lake fish assemblage has predictably shifted from one dominated by fluvial specialists (fantail darter and creek chub) to one dominated by habitat generalists common to lakes and reservoirs (bluntnose minnow, pumpkinseed sunfish and black crappie). Since 1975, species richness and diversity have increased at un-impounded sites along the Speed River. The occurrence of new species in Guelph Lake and upstream along the Speed River is attributed to the stocking of non-native species. Reductions in the distribution and abundance of certain fluvial specialists (fantail darter and northern hogsucker) are attributed to the flooding of riverine habitat and changes to downstream habitat conditions. Observed long-term changes to fish assemblage were not evident from earlier post-impoundment surveys.

Les changements touchant l'assemblage de poissons dans la rivire Speed ont t tudis il y a 27 ans aprs la cration du rservoir du lac Guelph. Des donnes recueillies en 2003 sur la pche l'lectricit et sur la pche aux filets ont t compares aux donnes des enqutes antrieures (1975) et postrieures (1976 et 1978) l'installation du rservoir. Depuis la cration du rservoir, l'assemblage de poissons du lac Guelph est pass, conformment aux prvisions, d'un assemblage domin par des espces fluviales (dard barr et mulet cornes) un assemblage domin par des espces gnrales de l'habitat propres aux lacs et aux rservoirs (ventre-pourri, crapet-soleil et marigane noire). Depuis 1975, la richesse et la diversit des espces se sont accrues des sites dpourvus d'un rservoir le long de la rivire Speed. L'apparition de nouvelles espces dans le lac Guelph et en amont le long de la rivire Speed est attribue au stockage d'espces exotiques. Les rductions dans la distribution et l'abondance de certaines espces fluviales (dard barr et meunier tte carre) sont attribues l'inondation de l'habitat fluvial et aux changements touchant les conditions de l'habitat en aval. Les changements long terme observs touchant l'assemblage de poissons n'taient pas vidents selon les premires tudes aprs l'installation du rservoir.