Lake Trout Spawning Habitat Selection in the Drummond Island Refuge: Paradigm or Paradox?

Despite over 50 years of stocking, the recovery of Great Lakes lake trout has been slow, potentially reflecting an inability of hatchery-reared lake trout to select habitats suitable for the successful incubation of eggs. We addressed this hypothesis using a novel acoustic telemetry-based approach to apportion sampling effort based on behavior of tagged lake trout. In 2013-14, 70 sites covering three reefs were physically characterized, surveyed for egg deposition and evaluated for incubation success using an in situ habitat bioassay. Egg deposition was confirmed at 21 sites and logistic regression/AIC were used to quantitatively rank the importance of physical characteristics to predicting the presence of eggs. Initial analyses indicated that substrates selected for egg deposition were more uniform, smaller in diameter, had deeper interstitial depth, and greater bathymetric slope than sites not selected. Additionally, sites selected for egg deposition had the highest incubation success, suggesting lake trout were capable of finding suitable spawning habitat within the Refuge. Nonetheless, lake trout spawned on a variety of substrates, including several that were inconsistent with the lake trout spawning habitat paradigm. Interestingly, these sites also produced viable fry, forcing us to rethink, adapt, and expand our conceptual understanding of suitable trout spawning habitat.