Tracking fish using 'buoy-based' GPS telemetry

The marine environment imposes severe constraints on the means by which location information can be obtained from submerged, freely swimming animals. Standard methods of tracking marine organisms are often labour intensive, expensive, or of low spatial and temporal resolution. Here, we describe a new method by which larger species of fish that live in shallow or surface waters can be tracked using an inexpensive telemetry device based on the global positioning system (GPS). We fixed small GPS data-logger units configured to record position fixes at 90 to 150 s intervals to low-drag tow-bodies and then attached these units by means of a tether to New Zealand eagle rays Myliobatis tenuicaudatus. After deployment periods lasting up to 29 h we recovered the tracking gear and downloaded the location data, which were stored onboard. The GPS units worked well, with mean fix-success rates >90%, and allowed accurate reconstruction of the movements of the rays throughout an estuary in Northland, New Zealand. Although our method is restricted to animals that swim on or near the surface of the water, it does provide a means of cheaply describing the movement patterns of suitable species for substantial periods of time at heretofore unprecedented spatial and temporal scales.