The Grouper Moon Project is the Caribbean’s oldest continuous grouper spawning aggregation research program, and represents one of the most advanced, multi-faceted tropical fisheries research programs in the world. Scientific products stemming from the project aim to support science-informed policies that will faciliatate healthy grouper fisheries in the Cayman Islands in the coming years, while maintaining the Cayman Islands’ global leadership in collaborative tropical fisheries research and management. Since 2001, REEF and our collaborators have published several scientific papers sharing results from the research.


Egerton, JP, AF Johnson, L Le Vay, CM McCoy, BX Semmens, SA Heppell, and JR Turner. 2017. Hydroacoustics for the discovery and quantification of Nassau grouper (Epinephelus striatus) spawning aggregations. Coral Reefs. 36 (2): 589-600

The Grouper Moon Project is always looking for new and/or better ways of accurately estimating the number of spawning Nassau Grouper at the aggregation sites being monitored. In 2014, we tested the use of a split-beam echosounder as a tool for surveying the abundance and size of fish at the aggregation site; the results of the study are detailed in this peer-reviewed paper. We found that the echosounder performs fairly well at providing an index of abundance, although the absolute accuracy of the method was not sufficient to replace other survey methods (e.g. mark and recapture monitoring). After calibrating the method with diver-based fish length surveys, the tool was able to accurately capture estimates of aggregating fish sizes. Surveys on all 3 islands (Little Cayman, Cayman Brac, and Grand Cayman) showed that the average size of Nassau Grouper on Little Cayman was significantly larger than on both Brac and Grand. On the other hand, the sizes of Nassau Grouper on Brac and Grand were not significantly different. Based on this study, the echosounder is a potentially useful tool for surveying aggregations, but is likely best use to complement more intensive diver-based survey methods. View paper online.

Bernard, AM, KA Feldheim, R Nemeth, E Kadison, J Blondeau, BX Semmens, MS Shivji. 2016. The ups and downs of coral reef fishes: the genetic characteristics of a formerly severely overfished but currently recovering Nassau grouper fish spawning aggregation. Coral Reefs. 35:273–284

Like many places throughout the Caribbean, Nassau Grouper spawning aggregations in the US Virgin Islands were overfished until their disappearance in the 1970s and 1980s. In the early 2000s, however, Nassau Grouper were found gathering at Grammanik Bank, USVI, a mesophotic coral reef adjacent to one of the extinct aggregation sites, and regulatory protective measures were implemented to protect this fledgling aggregation. The authors of this study addressed two objectives: 1) which factors (local vs. external recruitment) are important in shaping recovery of the USVI spawning aggregations, and 2) the impact of severe past overfishing on the genetic structure of the Gremmanik Bank aggregation. For this second objective, REEF Grouper Moon Project scientists provided genetic samples from individual Nassau Grouper taken from the Little Cayman spawning aggregation, a much larger and less impacted aggregation. No population structure was detected between the USVI and Cayman spawning aggregations. Additionally, the USVI spawning population showed signs of a genetic bottleneck, typical of greatly reduced populations. These collective results suggest that external recruitment is an important driver of the USVI spawning aggregation recovery. These findings also provide a baseline for future genetic monitoring of the spawning aggregations.View the paper online.

Archer, SK, JE Allgeier, BX Semmens, SA Heppell, CV Pattengill-Semmens, AD Rosemond, PG Bush, CM McCoy, BC Johnson, CA Layman. 2014. Hot Moments in Spawning Aggregations: implications for ecosystem-scale nutrient cycling. Coral Reefs. 10.1007/s00338-014-1208-4

This paper presents results from a study conducted as part of REEF's Grouper Moon Project, evaluating the potential ecosystem-level effect of Nassau Grouper aggregations. In particular, the study looked at the impact the spawning aggregation has in creating biogeochemical "hot moments", which occur when a temporary increase in availability of one or more limiting nutrients results in elevated rates of biogeochemical reactions. In this case, the limited nutrients are nitrogen and phosphorus, and the temporary increase is resulting from all of the grouper poop that results when approximately 5,000 Nassau Grouper gather in a small area for 10 days during the spawning season. View the paper online.

Jackson, AM, BX Semmens, Y Sadovy de Mitcheson, RS Nemeth, SA Heppell, PG Bush, A Aguilar-Perera, JAB Claydon, MC Calosso, KS Sealey, MT Schärer, G Bernardi. 2014. Population structure and phylogeography in Nassau Grouper (Epinephelus striatus), a mass-aggregating marine fish. PLoS ONE. DOI: 10.1371/journal.pone.0097508

This study, co-authored by scientists from REEF's Grouper Moon Project, evaluated genetic connectedness between Nassau Grouper populations throughout the Caribbean. The authors obtained genetic tissue samples from 620 Nassau Grouper from 19 sites across 9 countries, including the Cayman Islands. They found evidence for strong genetic differentiation among Nassau Grouper subpopulations throughout the Caribbean. These results suggest that, despite a lack of physical barriers, Nassau grouper form multiple distinct subpopulations in the Caribbean Sea. Oceanography (regional currents, eddies) likely plays an important role in retaining larvae close to spawning sites at both local and regional spatial scales. These findings highlight the importance of conservation initiatives such at REEF's Grouper Moon program in the Cayman Islands. View the paper online.

Heppell, SA, BX Semmens, SK Archer, CV Pattengill-Semmens, PG Bush, CM McCoy, SS Heppell, BC Johnson. 2012. Documenting recovery of a spawning aggregation through size frequency analysis from underwater laser calipers measurements. Biological Conservation. 155: 119-127.

This paper presents a key technique that scientists from REEF and our Grouper Moon collaborators have used to monitor fish on the Little Cayman spawning aggregation that does not require the capture and handling of fish. We show that length-distribution data can be collected by divers using a video-based system with parallel lasers calibrated to a specific distance apart, and subsequently use those data to monitor changes in the size distribution over time. View the paper online.

Archer, S.K., Scott A Heppell, Brice X Semmens,Christy V Pattengill-Semmens, Phillippe G Bush, Croy M McCoy, Bradley C Johnson. 2012. Patterns of color phase indicate spawn timing at a Nassau grouper Epinephelus striatus spawning aggregation. Current Zoology. 58(1): 73 - 83

This paper summarizes shifts if color phase of individual Nassau grouper at the Little Cayman spawning site in the days leading up to spawning, based on 5 years of video data.View PDF 

Jackson, AM, BX Semmens, and G Bernardi. 2012. Characterization and cross-species amplification of microsatellite markers in Nassau grouper (Epinephelus striatus). Molecular Ecology Resources 12(5): 972- 974.

This paper is part of the larger body of genetic research being conducted on Nassau Grouper in the Caribbean. View PDF.

Whaylen, L., P.G. Bush, B.C. Johnson, K.E. Luke, C.M.R. McCoy, S. Heppell, B. X. Semmens, and M. Boardman. 2006. Aggregation dynamics and lessons learned from five years of monitoring at a Nassau grouper (Epinephelus striatus) spawning aggregation in Little Cayman, Cayman Islands, BWI. 57th Gulf and Caribbean Fisheries Institute Meeting Proceedings. 57:1-14

This paper summarized the first five years of monitoring of the Little Cayman West End aggregation, including a summary of spawning activity, total numbers of fish present at the aggregation each year, coloration, and behavior. View PDF

Semmens, B.X., K.E. Luke, P.G. Bush, C.M.R. McCoy, and B.C. Johnson. 2006. Isopod infestation of post-spawning Nassau grouper around Little Cayman Island. Journal of Fish Biology 69: 933-937

This paper documents attacks by the isopod Excorallana tricornis tricornis on Nassau grouper caught in Antillian fish traps during the post-spawning season of Spring 2005. Fish were being trapped in order to acoustically tag individuals from sites around Little Cayman Island in order to better understand what percentage of reproductive-size individuals attend the aggregation each year. The paper discusses the apparent energetic costs associated with spawning. This work was also presented as a posted at the 56th Gulf and Caribbean Fisheries Institute Meeting in 2005 (View PDF), and a summary of the poster is posted online. (View Poster)

Semmens, B.X., K.E. Luke, P.G. Bush, C.V. Pattengill-Semmens, B. Johnson, C. McCoy and S. Heppell. 2005. Investigating the reproductive migration and spatial ecology of Nassau grouper (Epinephelus striatus) on Little Cayman Island using acoustic tags – An Overview. 56th Gulf and Caribbean Fisheries Institute Meeting Proceedings. 56:1-8

This paper provides an overview of the acoustic tagging project that was initiated on Little Cayman Island in 2005. The project aims to better understand the sphere of influence that a spawning aggregation has on the island's population of Nassau grouper, as well the impact of harvest protections on local fish densities. View PDF

Whaylen, L., Pattengill-Semmens, C.V., Semmens, B.X., Bush, P.G. and M.R. Boardman. 2004. Observations of a Nassau Grouper (Epinephelus striatus) Spawning Aggregation Site In Little Cayman, Including Multi-Species Spawning Information. Environmental Biology of Fishes. 70: 305-313

This paper summarizes the findings from the 2002 REEF Grouper Moon Project, which documented the characteristics of a newly discovered Nassau grouper spawning aggregation. View PDF