Sound production as an indicator of red hind density at a spawning aggregation

Annual spawning aggregations of red hind Epinephelus guttatus form at predictable times and locations and have historically succumbed to overfishing. Monitoring the status and res- toration of aggregations is essential for evaluating the effectiveness of fishery management meas- ures. Passive acoustic and diver-based underwater visual census (UVC) techniques were used to develop an efficient method for estimating red hind density from sound production at spawning aggregations. Red hind sound production was recorded from November 2010 to April 2011 at Abrir la Sierra, Puerto Rico. UVC surveys were conducted during the spawning season to assess changes in red hind density over a fixed time and area. Sound recorded from 18:00 to 19:00 h Atlantic Standard Time (UTC � 4) was representative of total daily changes in red hind sound pro- duction and was selected for the development of an efficient density estimation model. Pro- nounced daily changes in sound production and density were observed after the December 2010 and January 2011 full moons. Two hourly sound level measurements were compared to densities estimated by UVC surveys, yielding significant linear regressions, which were used to predict changes in fish density as measured at the aggregation site. Passive acoustic methods allowed to predict changes in red hind density and habitat use at a higher temporal resolution than previ- ously possible with traditional methods. Red hind sound production and inferred densities can be monitored and analyzed efficiently for multiple aggregation sites simultaneously, documenting short-term and long-term changes in red hind densities at spawning aggregation sites and provid- ing important information for the support or development of management strategies.