Abundance and home range of great barracuda (Sphyraena barracuda) inhabiting coastal waters in the Northern Caribbean

Background/Question/Methods

Great barracuda are top predators of tropical marine systems. Given their use of a wide range of habitats, large global distribution and locally high abundances, barracuda can play an important ecological role, yet few studies quantify their spatial ecology. Tracking via passive acoustic telemetry is being conducted in Culebra, Puerto Rico and Buck Island Reef National Monument (BIRNM) in St. Croix, U.S. Virgin Islands. To date, 12 (mean length = 105.5cm, SD = 25cm) and 36 (mean length = 91.7cm, SD = 16.5cm) fish are being monitored in Culebra and BIRNM, respectively. Barracuda were sampled by trolling with heavy action recreational fishing gear and artificial lures. A random survey was undertaken to infer population abundance in the two locations. Randomization tests on the catch per unit effort (CPUE) data were used to compare population densities between sites. Home ranges were estimated using minimum convex polygons (MCP) and kernel density estimators (KDE) in order to compare habitat use as a function of fish size classes and between study sites, as well as to determine whether home range size estimates are consistent across these two commonly used methods. KDEs were also used to model habitat use across each study site.

Results/Conclusions

Randomization tests of CPUE data show highly significant differences between sites, with BIRNM containing higher densities of barracuda than coastal waters surrounding Culebra. So far, 392,150 reliable detections spanning 24 months in Culebra and 926,676 detections for 12 months in BIRNM have been processed and analyzed. MCP and KDE home range estimation showed similar results, with fish inhabiting distinct, overlapping home ranges of several kilometers. Home ranges that included 95% of fish activity space encompassed smaller areas of core activity (defined as 50% of activity space), with repeated but less frequent use of peripheral space. Habitat models showed all habitat types as significant for daily rates of detection, but indicated temporal variation in spatial patterns.