ASSESSMENT OF LAKE TROUT SPAWNING HABITAT AND EGG DEPOSITION AND SURVIVAL IN LAKE-ONTARIO

Identification of the amount of lake trout spawning habitat and its ac tual use by lake trout in Lake Ontario is important for re-establishme nt of this species. From a combination of hydrographic field data, bat hymetry measurements, and video observations, 20 reputed spawning site s, 14 of which were considered to be historically important were evalu ated for possible use by lake trout. Based on preliminary evaluations 13 of the 20 sites were rejected for further study because of inapprop riate substrate or excessive infilling of interstitial spaces. Additio nal, more intense evaluations were made of seven sites, five that were of historical importance and two that were man-made. These seven site s had areas of suitable spawning habitat of from 6 to 4,000 m(2), mini mal water depths of from 2.2 to 10.8 m, mean cobble diameters of 9.8-2 0.0 cm, and slopes of 20-45 degrees. Lake trout egg densities, estimat ed from. recoveries in egg nets deployed in 1992, ranged from a mean o f 6 to 6,200 eggs m(-2) and the highest densities were found at man-ma de sites. The actual egg deposition on the seven sites studied intense ly amounted to only 0.0003 to 0.6% of the potential deposition if all the lake trout that survived from stocking within a 30 km radius of ea ch site spawned there. Egg survival to the eyed stage ranged from 21 t o 82% and was inversely related to wind fetch. Spawning was earlier in western than in eastern Lake Ontario and was related to the rates of fall cooling. Duration of the spawning period ranged from 1 to 39 days but the low estimates were from collections of only a few eggs. A swi m-up mortality syndrome observed in eggs reared in a laboratory was hi gh, ranging from 31.0 to 74.5%. The potential for lake trout restorati on in Lake Ontario appears to be limited by a scarcity of good spawnin g sites, low egg deposition on spawning sites recognized by researcher s, and excessive swim-up mortality.