Lake trout spawning at five sites in Ontario waters of Lake Superior

To assess lake trout, Salvelinus namaycush, spawning on natural substrates, we studied five sites in Canadian waters of Lake Superior between 1987 and 1990. Lake trout were reported to spawn historically at three of these sites-Welcome Island, Hare Island, and near the Agawa River. No lake trout eggs were found at the Welcome Island site in 1987 or 1989. Eggs were found at the Agawa site in 1989 but not in 1988. Spawning occurred at Hare Island in 1987 and 1989 but egg deposition rates were < 20 eggs m(-2). Two other sites-Sinclair Cove and No Name Shoal-were studied because lake trout catches were high in gillnets set during autumn and substrate that might be suitable for spawning was nearby. Lake trout eggs were deposited at rates up to 370 eggs m(-2) in Sinclair Cove. No eggs were found at No Name Shoal. Egg deposition greater than 20 eggs m(-2) occurred in pebble, cobble and boulder substrates that had interstices extending between 20 and 120 cm below the substrate surface. Eggs were not found in substrates < 2 mm in diameter. Lake trout abundance, inferred from gillnet catches, at these five sites did not vary directly with egg-deposition rates. The site with the highest lake trout egg-deposition, Sinclair Cove A, was comprised of mobile substrate and its location, interstitial depth, and area changed among years presumably in response to wave action.