RECOGNITION OF SPAWNING AREAS BY LAKE TROUT - DEPOSITION AND SURVIVALOF EGGS ON SMALL, MAN-MADE ROCK PILES

Reproductive success of stocked lake trout (Salvelinus namaycush) in t he Great Lakes has been negligible in all of the lakes except Superior . Among the factors which may affect reproduction, the quality of spaw ning habitat and selection of good habitat by hatchery-origin lake tro ut are important for the success of population restoration. Stocked la ke trout may be unable to recognize small areas of appropriate spawnin g substrate. The purpose of this study was to identify characteristics of spawning substrate (e.g., depth, substrate size, reef contour) tha t are important for spawning site selection by lake trout, and to asso ciate these characteristics with egg incubation success. Six rock pile s, 4.5 m in diameter, were constructed 80 m from a natural spawning re ef Egg deposition and survival to hatching were measured on and adjace nt to the rock piles and on the nearby natural cobble reef Lake trout spawned on all of the rock piles in 1990 and 1991. Few eggs were colle cted immediately adjacent to the piles. Egg densities on the piles wer e two to four times lower than on the natural cobble reef that was muc h larger in area. These data indicate that spawning site selection by lake trout was influenced by substrate size and location. Egg survival was high in incubators buried in rock piles (38-61%) and natural cobb le (27-59%), but low in incubators adjacent to the piles (3-10%) and o n sandy substrates (9%). Thus, lake trout detected and spawned on smal l areas of clean cobble that supported egg incubation. Lake trout will use new areas of substrate even when larger natural areas are availab le within 100 m. This result indicates that lake trout spawning on har bor breakwalls and man-made rubble piles is due to their attraction to clean substrate rather than the absence of natural substrate nearby.