SPAWNING PATTERNS AND INTERSPECIFIC MATINGS OF SYMPATRIC WHITE (CATOSTOMUS-COMMERSONI) AND LONGNOSE (C-CATOSTOMUS) SUCKERS FROM THE GOUIN RESERVOIR SYSTEM, QUEBEC

White (Carostomus commersoni) and longnose (C. catostomus) suckers fro m the Gouin reservoir, Quebec, and a small upstream lake (Lac des Cinq Miles) spawned in the same stream. White suckers numerically dominate d the runs in all years; however, abundances of both species decreased eightfold during a year when the reservoir level was lowered for main tenance. Return rates of individuals of both species tagged during the spawning run were poor in the following year, and only a few fish (<0 .6%) skipped a year to spawn 2 years later. Although some individuals of both species occurred at all monitored spawning areas, white sucker s concentrated their spawning activity over sites with boulders, where as longnose suckers were most abundant over gravel. Differences in the courtship behaviour of the mio species initially discouraged interspe cific matings. However, white sucker males ultimately participated in 32% of the female longnose sucker matings, though spawning of male lon gnose suckers with female while suckers was not observed. White sucker s spawned in groups or in pairs, whereas in all instances longnose suc kers spawned with two or more males.