We used radio-linked ultrasonic (acoustic) positioning to unobtrusively monitor and record activity of groupers during and after spawning on the Great Barrier Reef in Australia (in association with James Cook University in Townsville, Queensland).  We collected over 200 MB of 3-D movement data over 81 days with sub-metre accuracy from coral trout (Plectropomus leopardus) at One Tree Island, located in the southern part of the reef.  Results from the analysis of these data along with work conducted by other researchers may be used in the design and location of marine protected areas to help manage and replenish populations of coral trout - a species vulnerable to over-exploitation.  For this work, we successfully tracked detailed movement and mapped habitat of fish in arguably the most complex and threatened marine environment on the planet.