Acoustic telemetry is a widely used technique employed to better understand fish movement patterns across seascapes. Traditionally, surgical acoustic transmitter implantation is conducted at the surface, resulting in a high degree of uncertainty as to the post-release survival of the fish and the validity of the results attained from these experiments. Few studies have conducted In situ tagging, where the capture, tagging, and release are completed entirely at the depth in which the fish occurs naturally. Through the use of closed-circuit rebreather (CCR) technology, this study outlines the first known practical application of the methodology performed at mesophotic depths. In six dives conducted at depths between 40 and 50 m, a total of 10 Nassau grouper were tagged at a spawning aggregation off the west coast of Puerto Rico. The total time (time divers arrived at the trap to time of release) for each procedure was approximately 12 min, after which all fish were released and observed without indication of stress or physiological impairment. Short-term tracking of tagged fish revealed a 100% post-surgery survival rate with maximum detection of 347 days post-surgery. Survival rates of this nature have not been quantified or reported from other tagging studies, allowing the researchers to conclude that this methodology, coupled with the efficiency provided by CCR at these depths, enhanced survivorship and bias for studies utilizing acoustic telemetry.

Understanding animal space use patterns is critical for ecological research and conservation efforts. An organism’s home range territory serves as the fundamental unit of space use and is the area repeatedly used for routine activities. Nassau grouper, Epinephelus striatus, once of high commercial fishery importance, are now on the IUCN’s Red List designated as Critically Endangered due to overexploitation. Known for the formation of large spawning aggregations, information on their movements and space use dynamics outside of the reproductive period are lacking. In this study, we used acoustic telemetry to quantify the non-spawning horizontal and vertical space use patterns of Nassau grouper at the Bajo de Sico seamount, a seasonally closed marine protected area (MPA) in Puerto Rico. Twenty-nine groupers were tagged with acoustic transmitters, of which, fourteen were tracked continuously over a three-year period. Tagged individuals displayed high site fidelity to home reef locations and individuals occupied home ranges of relatively small size that remained constant between years. There was a high degree of overlap of home range territories and in locations where multiple individuals occupied the same home reef, individuals maintained discrete vertical distributions. Nassau groupers were recorded making multiple forays to the spawning site outside of the reported spawning season, and two individuals underwent home reef site relocation. Results indicate relatively low contribution to ecological connectivity during the non-reproductive period, therefore high relative abundances of this species are needed to fulfill their ecological role at the community level. The results also highlight the importance of Bajo de Sico, an isolated seamount of relatively deeper depth, as critical habitat for primary home reef sites of Nassau grouper. These results provide a basis for adapting the current management strategy at this MPA to provide adequate protection to the non-spawning population of Nassau grouper.

Caribbean populations of the long-spined black sea urchin Diadema antillarum Philippi were decimated by a disease-induced mass mortality in the early 1980’s. The present study provides an updated status of the D. antillarum recovery and population characteristics in La Parguera Natural Reserve, Puerto Rico. The last detailed study to assess population recovery in 2001, indicated a slow, and modest recovery, albeit densities remained far below pre-mass mortality levels. Population densities were assessed along three depth intervals in six reef localities and one depth in three lagoonal sea-grass mounds using ten 20 m2 (10 × 2 m) belt-transects at each depth interval. Most of these were previously surveyed in 2001. All individuals encountered along the belt transects were sized in situ with calipers and rulers to characterize the size (age) structure of each population and get insight into the urchin’s population dynamics and differences across localities in the area. Habitat complexity (rugosity) was assessed in all depth intervals. No significant differences in population densities between reef zones (inner shelf and mid-shelf) were observed, but significantly higher densities were found on shallow habitats (<5 m depth; 2.56 ± 1.6 ind/m2) compared to intermediate (7–12 m; 0.47 ± 0.8 ind/m2) and deep (>12 m; 0.04 ± 0.08 ind/m2) reef habitats in almost all sites surveyed. Habitat complexity had the greatest effect on population densities at all levels (site, zone and depth) with more rugose environments containing significantly higher densities and wider size structures. Comparison between survey years revealed that D. antillarum populations have not increased since 2001, and urchins seem to prefer shallower, more complex and productive areas of the reef. Populations were dominated by medium to large (5–9 cm in test diameter) individuals and size-frequency distributions indicated that smaller juveniles were virtually absent compared to 2001, which could reflect a recruitment-limited population and explain in part, the lack of increase in population densities. The limited temporal scale of this study, high horizontal movement of individuals along the complex, shallower reef and inshore habitats could also explain the general decline in mean densities. Other extrinsic factors affecting reproductive output and/or succesful recruitment and survival of juveniles likely contribute to the high variablility in population densities observed over time.

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