This work was presented at the OCEANS19 meeting, and was a result of research done as part of the Grouper Moon Project. More than 800 species of fish produce sound including Red Hind (Epinephelus guttatus), Nassau Grouper (E. striatus), Black Grouper (Mycteroperca bonaci), and Yellowfin Grouper (M. venenosa). Their sounds can be used to monitor these fish and may be a means to estimate abundance if parameters such as source levels, detection probabilities, and cue rates are known. During the week of Nassau Grouper spawning in February 2017, a passive acoustic array was deployed off Little Cayman in the Cayman Islands to study the temporal and spatial dynamics of spawning aggregations of Nassau Grouper and Red Hind, and measure the source levels of the sounds produced by all four species. The localization method was based on hyperbolic localization of cross-correlated time differences of arrival and its accuracy evaluated via simulations and empirical measurements. The high number of localizations at fish spawning aggregations suggests that localization can be used to accurately measure source levels, detection ranges, and other variables needed for density estimation of spawning aggregations.