EVIDENCE OF LAKE TROUT SPAWNING ON A DEEP REEF IN LAKE MICHIGAN USINGAN ROV-BASED EGG COLLECTOR

We report the first evidence of egg deposition by stocked lake trout i n deep water in the Great Lakes, on Julian's Reef in Lake Michigan. Hi storic information, and current data from Lake Superior, suggest that many native lake trout spawned in deep water, and therefore some stock ing efforts have been focused on deep reefs. However, no evidence has been previously found to indicate that stocked lake trout spawn in are as deeper than 20m. The purpose of this study was to find evidence of lake trout spawning on Julian's Reef in Lake Michigan, a deepwater ree f (minimum depth 27 m) which was an important spawning site for native strains of lake trout. We used a Phantom S2 ROV equipped with a sucti on sampler to obtain visual observations of lake trout and to collect eggs and egg predators (slimy sculpins). Five loose lake trout eggs an d four sculpins were recovered; the three largest sculpins contained n ine trout eggs. Adult lake trout were seen at rates above one per minu te, in contrast to less than half that rate seen with similar equipmen t at Burns Harbor breakwell in Lake Michigan. We suggest future modifi cations of robotic ROV equipment to enhance in situ collections of lak e trout eggs and culpins.