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 actual use by lake trout in Lake Ontario is important for re-establishment of this species. From a combination of hydrographic field data, bathymetry measurements, and video observations, 20 reputed spawning sites, 14 of which were considered to be historically important were evaluated for possible use by lake trout. Based on preliminary evaluations 13 of the 20 sites were rejected for further study because of inappropriate substrate or excessive infilling of interstitial spaces. Additional, more intense evaluations were made of seven sites, five that were of historical importance and two that were man-made. These seven sites had areas of suitable spawning habitat of from 6 to 4,000 m(2), minimal water depths of from 2.2 to 10.8 m, mean cobble diameters of 9.8-20.0 cm, and slopes of 20-45 degrees. Lake trout egg densities, estimated from. recoveries in egg nets deployed in 1992, ranged from a mean of 6 to 6,200 eggs m(-2) and the highest densities were found at man-made sites. The actual egg deposition on the seven sites studied intensely 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 each site spawned there. Egg survival to the eyed stage ranged from 21 to 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 swim-up mortality syndrome observed in eggs reared in a laboratory was high, ranging from 31.0 to 74.5%. The potential for lake trout restoration in Lake Ontario appears to be limited by a scarcity of good spawning sites, low egg deposition on spawning sites recognized by researchers, and excessive swim-up mortality.