The Cayman Islands Department of Environment needs to assess the effectiveness of Nassau grouper (Epinephelus striatus) spawning aggregation site closures by gaining a better understanding of how local grouper populations use the ag- gregation sites. During the January 2005 spawning season thirty Nassau grouper were acoustically tagged off the Little Cayman west end aggregation site and during the summer of 2005 an additional twenty Nassau groupers were tagged around Little Cayman. By tagging fish on the aggregation we have been able to determine where fish go after they leave the spawning aggregation. By tagging fish around Little Cayman prior to the 2006 spawning season we will be able to de- termine the proportion of fish from around the Island that attend the west end spawning aggregation. Also, the frequency of aggregation attendance by individual fishes as a function of demography will be assessed. Initial results show that 60% of the groupers tagged during the January, 2005 aggregation returned to aggregate during the February full moon. Further- more, these 18 returning fish were amongst the largest of the 30 tagged. Ultimately, this information will allow us to assess the current and future impacts of protections afforded Cayman’s spawning aggregations. Moreover, the study will define an aggregation’s “sphere of influence” both geographically and demographically and will thus aid in the management of local Nassau grouper populations.