Reproduction, croissance et morphologie comparées des Grands Corégones (Coregonus clupeaformis) nains et normaux du réservoir Outardes-2 (Québec)

Abstract

Fall experimental fishing for spawners and drift net samples of eggs revealed the presence of sympatric populations of dwarf and normal lake whitefish in Outardes-2 Reservoir. Dwarfs mature at a younger age (1 + vs. 4 + ) than normal spawners. They also show a much slower growth rate, a lower absolute fecundity (1009 vs. 9787 eggs), a higher relative fecundity (32.2 vs. 11.8 eggs/g), and a smaller ovarian egg diameter (1.60 vs. 2.63 mm). Four morphometric variables out of the 13 measured differed significantly between the two forms, including the length and depth of the caudal peduncle and the diameter of the orbit; six out of the seven meristic variables that were enumerated also differed between the two forms, including the number of gillrakers on the first gill arch (dwarfs, 24.7; normal whitefish, 25.9). Reproductive isolation is virtually nonexistent, the two forms using the same spawning site, with a minimal time lag between their mean dates of egg deposition (1983: normal whitefish, November 15 and dwarfs, November 22; 1984: normals, November 9 and dwarfs, November 12). The characteristics associated with dwarfism in the various sympatric populations of Coregonus clupeaformis are discussed.