Probability of detecting (A) and positioning (B) V6 and V7 oviduct transmitters (VEMCO, Halifax, Canada) following expulsion into substrate at known spawning sites in the Drummond Island Lake Trout Refuge, Lake Huron. V6 transmitters operated at 180 kHz and V7 transmitters operated at 69 kHz. Control transmitters were suspended 1 m above the substrate. Transmitter type had no significant effect on probability of detection or positioning (linear mixed model: P <0.001); however, oviduct transmitters in the substrate were significantly less likely to be detected and positioned than control transmitters (linear mixed model; P <0.001 for both detection and positioning). Seventy-eight percent of oviduct transmitters in the substrate were not positionable.