USE OF EGG TRAPS TO INVESTIGATE LAKE TROUT SPAWNING IN THE GREAT-LAKES

Disk-shaped traps were used to examine egg deposition by lake trout (S alvelinus namaycush) at 29 sites in the Great Lakes. The main objectiv es were to; first, evaluate the disk trap as a device for sampling lak e trout eggs in the Great Lakes, and second, summarize what has been l earned about lake trout spawning through the use of disk traps. Of the 5,085 traps set, 60% were classified as functional when retrieved. Ev idence of lake trout egg deposition was documented in each of the lake s studied at 14 of 29 sites. A total of 1,147 eggs were trapped. The p ercentage of traps functioning and catch per effort were compared amon g sites based on depth, timing of egg deposition, distance from shore, size of reef and type of reef(artificial or natural). Most eggs were caught on small, shallow, protected reefs that were close to shore. Us e of disk traps on large, shallow, unprotected offshore reefs or along unprotected shorelines was generally unsuccessful due to the effects of heavy wind and wave action. Making multiple lifts at short interval s, and retrieval before and re-deployment after storms are recommended for use in exposed al eas. On large reefs, preliminary surveys to ide ntify preferred lake trout spawning habitat may be required to deploy disk traps most effectively. Egg deposition by hatchery-reared fish wa s widespread throughout the Great Lakes, and the use of artificial str uctures by these fish was extensive.