LAKE TROUT SPAWNING HABITAT IN THE GREAT-LAKES - A REVIEW OF CURRENT KNOWLEDGE

We review existing information on lake trout spawning habitat, which m ight indicate whether habitat is now a limiting factor in lake trout r eproductive success. Lake trout spawning habitat quality is defined by the presence or absence of olfactory cues for homing, reef location w ith respect to the shoreline, water depth, proximity to nursery areas, reef size, contour, substrate size and shape, depth of interstitial s paces, water temperature at spawning time, water quality in interstiti al spaces, and the presence of egg and fry predators. Data on factors which attracted native spawners to spawning reefs are lacking, due to the absence of historic data on egg deposition. No direct evidence of egg deposition has been collected from sites deeper than 18 m. Interst itial space and, therefore, substrate size and shape, appear to be cri tical for both site selection by adults and protection of eggs and fry . Water quality is clearly important for egg incubation, bur the criti cal parameters which define water quality have not yet been well deter mined in the field. Exposure to wave energy, dictated in part by reef location, may maintain high water quality but may also damage or dislo dge eggs. The importance of olfactory cues, water temperature, and pro ximity to nursery habitat to spawning trout is unclear. Limited data s uggest that egg and fry predators, particularly exotic species, may cr itically affect fry production and survival. Although availability of physical spawning habitat is probably not limiting lake trout reproduc tion, changes in water quality and species composition may negatively affect early life stages. This review of habitat factors that affect e arly life stages of lake trout suggests several priorities for researc h and management.