Map of Drummond Island Lake Trout Refuge field study site used for testing the ability of the VEMCO Positioning System (VPS) to position lake trout oviduct transmitters after they are expelled into substrate. Left: Location of the refuge in Lake Huron (North America; shown in orange). The blue star indicates the actual study site (45°55.840ˈ N, 83°39.572ˈ W). Right: Location of three small VPS arrays (at known lake trout spawning sites) overlaid on high-resolution multibeam sonar bathymetry. Blue squares indicate location of receivers and white circles represent test transmitter locations. One transmitter at each test transmitter location was suspended 1 m above the substrate to act as a control and two more were placed in the substrate. A synchronization transmitter was placed at the central test transmitter site to synchronize receiver clocks.