Evidence of Lake Trout Spawning on a Deep Reef in Lake Michigan Using an ROV-Based Egg Collector

Abstract

We report the first evidence of egg deposition by stocked lake trout in deep water in the Great Lakes, on Julian's Reef in Lake Michigan. Historic information, and current data from Lake Superior, suggest that many native lake trout spawned in deep water, and therefore some stocking efforts have been focused on deep reefs. However, no evidence has been previously found to indicate that stocked lake trout spawn in areas deeper than 20 m. The purpose of this study was to find evidence of lake trout spawning on Julian's Reef in Lake Michigan, a deepwater reef (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 suction sampler to obtain visual observations of lake trout and to collect eggs and egg predators (slimy sculpins). Five loose lake trout eggs and four sculpins were recovered; the three largest sculpins contained nine trout eggs. Adult lake trout were seen at rates above one per minute, in contrast to less than half that rate seen with similar equipment at Burns Harbor breakwall in Lake Michigan. We suggest future modifications of robotic ROV equipment to enhance in situ collections of lake trout eggs and sculpins.