Abstract

Fish spawning aggregations (FSAs) are a vital part of the life cycle of many reef fish species. In many cases, a lack of knowledge of the location of FSA sites prohibits their protection and effective management. Therefore, practical approach-es to identify undocumented sites and assess their utilization by aggregating species are needed. We used acoustic technol-ogies at reported FSA sites in the Florida Keys, USA, to accomplish two objectives: i) Assess whether reported FSA sites are characterized by similar habitat characteristics, with a focus on geomorpho-logical features, and ii) Assess reef fish utilization patterns of reported FSA sites, including multiple sites reported to have been “fished out” in previous decades. To characterize geomorphological features at FSA sites, we used a commercial single-beam acoustic seabed classifica-tion system [QTCView Series V; Quester Tangent Corp., Sidney, BC, Canada; see Gleason et al. 2006] to map historical FSA sites in the upper and lower Florida Keys. Results from the upper FL Keys indicated that drowned, margin-parallel, rocky ridges, known locally as outlier reefs, are features found in proximity to all FSA sites studied (n = 6 sites; Gleason et al. In press). Reported FSA sites in the lower Keys (n = 4 sites) were also mapped in proximity to outlier reefs. In both the upper and lower Keys, the reported FSAs were located near steep slopes. For the fish utilization component, we used split-beam acoustic surveys (120kHz; hereafter “fisheries sonar”) and diver surveys to assess and groundtruth, respectively, fish occurrence and abundance patterns at reported FSA sites. In the upper FL Keys, fisheries sonar and diver surveys were performed in 2009 - 2010 at reported FSA sites during predicted full-moon spawning periods for snappers (summer 2009) and groupers (winter 2010). Surveys confirmed that the snapper aggregation sites continue to be targeted by commercial snapper-grouper vessels during known snapper spawning periods. No fishing was observed at grouper aggregation sites during winter full-moon surveys, a result of recent South Atlantic Fisheries Management Council-enacted regulations prohibiting the landing of shallow-water grouper species during the months of January-April. Moderately elevated densities (relative to densities typically observed in the FL Keys) of mutton snapper (Lutjanus analis; n = 2 sites), cubera snapper (L. cyanopterus; n = 1 site) and black grouper (Mycteroperca microlepis; n = 1 site) were observed on scuba surveys during predicted spawning moons, as were those of several non-snapper-grouper species. However, no aggregations or specific spawning behaviors were observed. In the lower FL Keys, fisheries sonar and diver surveys were performed in 2010 at reported gray snapper (Lutjanus griseus; n = 3 sites) aggregation sites (Lindeman et al. 2000) during predicted full-moon spawning periods. Positive signs of aggregated gray snapper were observed at multiple locations near Key West, including one site where relatively large (~ 35 - 50 cm FL) gray snapper were observed over multiple days in aggregations totaling many hundreds of fish (one diver estimated ~ 800 fish in his field of view, and the aggregation appeared to extend beyond his field of view). Although positive signs of aggregations have been observed during this ongoing research, particularly in the lower Keys, actual spawning has not yet been observed. Additional surveys are planned in 2011. From a manage-ment perspective, results from this project demonstrate the benefit of using acoustic and habitat-based approaches to identify critical reef fish aggregation sites for additional monitoring, research and management focus.

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