Two VR2 units used in range testing in San Francisco Bay. Both units have a small white tag attached to them, which records the depth, pitch and roll of the unit while it is recording tag transmissions.


Photo: Bridge Attachment

Submersible, automated ultrasonic receivers (Vemco, Ltd., VR2, VRW) are used to detect the coded beacons. We utilize a shipboard receiver (Vemco Ltd., VR100) and a directional hydrophone to track individuals carrying continuous tags. The VR2 and VRW (wireless bluetooth equipped) units are secured with hose clamps to a 1-meter length of 1/4-inch stainless steel cable that is held upright in the water by a buoy. The cable is affixed to an anchor/mooring that has a second, longer section of cable attached to a stationary object such as a tree or bridge abutment. The cable, anchor and monitor are then extended out from the attachment point to a distance determined by channel width, depth, and flow.

In areas where the water is too deep or wide to effectively use a mooring cabled off to shore, an acoustic release is often used. The automated monitor is attached to a heavy-duty line hooked to the top of an acoustic release, and topped with a hard plastic float. The bottom of the acoustic release is secured to an anchor/mooring. The VR2 monitor will be recovered when the acoustic release is triggered and it releases from the mooring and floats to the surface.