Home range, space use, and vertical distribution of Nassau grouper (Epinephelus striatus) during non-spawning times in Western Puerto Rico

Abstract

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.

Spatial and temporal dynamics of a Nassau grouper fish spawning aggregation located on an isolated seamount in Puerto Rico

“…Additionally, during the 2014 and 2016 tracking periods, three tagged fish migrated to the FSA site in relation to the April and May full moons that corresponded to the spawning lunar periodicity observed for this location (Tuohy et al, 2023). All these latter migrations resulted in less than 24 hours spent at the aggregation site and fish migrated separately.…”

“…In 2015, aggregations were associated with full moons from January to March; however, an increased number of tagged fish were detected at the FSA site during the full moon in April. Indications of aggregation formation were not observed, neither in tag presence nor visual census, to be associated with the April full moon in other years studied with acoustic tags (Tuohy et al, 2023). In 2016, the aggregation observed in April was associated with the expected timing of the lunar cycle, but with the March full moon occurring late in the month (23/24 March), the subsequent timing of the aggregation formed in April (Figure 2).…”

“…Kruskall–Wallis H ‐tests were used to test for significant differences in spawning habitat use (50% and 95% UDs) between years. A Wilcoxon rank‐sum test was used to test for difference in spawning and non‐spawning habitat use (Tuohy et al, 2023) between years.…”

“…Kruskall-Wallis H-tests were used to test for significant differences in spawning habitat use (50% and 95% UDs) between years. A Wilcoxon rank-sum test was used to test for difference in spawning and non-spawning habitat use (Tuohy et al, 2023) between years. Monthly and daily detection rates and tag presence were graphed to indicate periods of peak presence at the FSA site.…”

“…Following the spawning season, all fish returned to their respective home reef locations (Tuohy et al, 2023). The total combined spawning core area (50% UD) and home range (95% UD) encompassing all 14 resident tagged fish detected within the full array during the spawning season were 0.79 and 1.86 km 2 , respectively, with no significant differences between core area (50% UD, W(2) = 64.0, P = 0.12) and home range (95% UD, W…”