Mobile receivers: releasing the mooring to 'see' where fish go

Much has been learned from the large scale deployment of acoustic tags on aquatic species and associated networks of riverine and marine receivers. While effective in the linear environment of river systems, marine systems limit the ability to provide spatial information on fish movements and distributions due to a combination of costs, logistics, and lack of off-shore technology. At the same time, each year millions of dollars worth of tags are being released into the aquatic environment with extended battery/transmission life, yet detections are limited to coastal arrays. Here we explore new methods of tracking acoustically tagged species in the marine environment. A new miniaturized acoustic receiver, the Vemco Mobile Transceiver (VMT) can be carried by large marine organisms. In combination with satellite and archival tag technology, VMTs were deployed on northern elephant seals to monitor acoustic tags encountered during their migrations across the Northeast Pacific. Early results include acoustic detections of tagged great white sharks, salmon sharks, Chinook salmon, steelhead, lingcod, green sturgeon and other elephant seals. We also propose several alternative directions for future effort: 1) analyzing the growing number of passive acoustic survey recordings made from hydrophone arrays for acoustic tag detections, 2) working with acoustic technology providers to develop hull-mounted receiver systems for the thousands of ocean going vessels around the world and 3) integrating acoustic receiver technology into the thousands of moored and drifting oceanographic buoy arrays.