USE OF A REMOTELY OPERATED VEHICLE TO STUDY HABITAT AND POPULATION-DENSITY OF JUVENILE LAKE TROUT

We determined the feasibility of using a remotely operated vehicle (RO V) to observe juvenile lake trout Salvelinus namaycush. The ROV was eq uipped with a high-resolution, low-light, black-and-white video camera and two halogen headlamps and was tethered by a 152-m umbilical cable . We used the ROV to sample two central Ontario lakes: Source Lake in summer and fall and Lake Opeongo in summer. We surveyed the lake botto m at depths of 2.5-40 m in both lakes during day and night. The ROV tr aveled slightly above the substrate recording a field of view 1.8 m wi de and 0.3-0.5 m high at a distance of 1.8 m in front of the ROV. Over all, 54,594 m(2) of lake bottom were sampled, and 114 juvenile lake tr out (<300 mm, total length) were observed. Juvenile lake trout exhibit ed minimal avoidance of the ROV with some individuals being observed f or several minutes (mean, 41.6 s). The observed distribution suggested movement to shallower habitat at night. Mean (+/-SE) lake trout densi ties varied between the study lakes for depths of 5-25 m (Opeongo: 5.2 +/- 2.0 fish/ha; Source: 25.9 +/- 6.5 fish/ha), which was consistent with catch per unit effort in small-mesh gill nets for these lakes (Op eongo: 0.9 +/- 0.1 fish/net-night; Source: 5.8 +/- 0.4 fish/net-night) . The ROV allowed nonlethal sampling and direct estimation of fish den sity, thereby offering a good alternative to conventional netting tech niques.