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 facilitate 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.

Stock, BC, AD Mullen, JS Jaffe, A Candelmo, SA Heppell, CV Pattengill-Semmens, CM McCoy, BC Johnson, and BX Semmens. 2023. Protected Fish Spawning Aggregations as Self-replenishing Reservoirs for Regional Recovery. Proceedings of the Royal Society B.

This study addresses the question of where fertilized eggs go after being released by Nassau Grouper at their spawning site off the west end of Little Cayman. On nights of spawning in 2017, researchers physically tracked clouds of tiny, transparent Nassau Grouper eggs through the night with an underwater microscope developed by scientists at Scripps Oceanography. Results show that fertilized eggs from Little Cayman floated back onto reefs on the island. Drawing on these direct observations and ocean current data collected on spawning nights at Little Cayman, the authors also used a computer model to investigate where the fertilized eggs likely went in 2011 and 2016. The model predicted that many of the baby Nassau Grouper ended up back at Little Cayman in 2011, a suggestion that dovetails with prior research (Stock et al 2021) showing that the 2011 reproductive season led to a significant population increase around Little Cayman (Waterhouse et al 2020). For 2016, the model predicted that currents carried some fertilized eggs to the nearby island of Grand Cayman. This study highlights how reproductive success and the final destination of the grouper eggs can vary from year to year, while also showing that local conservation measures to protect Nassau Grouper are boosting local populations and sometimes providing spillover benefits to neighboring islands. View Online

Sleugh, T, CM McCoy, CV Pattengill-Semmens, BC Johnson, SA Heppell, L Waterhouse, BC Stock, and BX Semmens. 2023. Migratory Behavior of Aggregating Male Tiger Grouper (Mycteroperca tigris) in Little Cayman, Cayman Islands. Environmental Biology of Fishes.

This study, conducted as part of the Grouper Moon Project, reports on the movement patterns and spawning behavior of Tiger Grouper during their reproductive season. Tiger Grouper is one of over 20 species of reef fish that are known to use the western tip of Little Cayman in the Cayman Islands as a spawning ground. This multi-species aggregation is best known for being home to the largest and one of the last known spawning aggregations of Nassau Grouper. Unlike the mass spawning behavior seen with Nassau Grouper, male Tiger Grouper defend territories to attract mates in a lek-like reproductive strategy. Tiger Grouper spawn during winter full moons, typically a few days after the Nassau Grouper. The Grouper Moon research team acoustically tagged ten spawning male Tiger Grouper at the Little Cayman spawning aggregation. Using a hydrophone array surrounding the island, the researchers tracked the movements of the tagged fish for 13 months. The authors observed 3 migratory strategies: resident fish that live at the aggregation site, neighboring fish that live within 4 km of the site, and commuter fish that travel over 4 km for spawning. Fish began aggregating 2 days before the full moon and left the aggregation site 10–12 days after the full moon, from January to May. This research helps shed light on an important, but poorly studied, member of Caribbean coral reef ecosystems. Tiger Grouper reach sexual maturity around two years of age, and live at least nine years. They are protogynous hermaphrodites, meaning they start life as female and then change to male as they get larger. They are largely piscivorous, and play an essential ecological role in structuring coral reef food webs. View Online

Layton, J, A Candelmo, BX Semmens, C Pattengill-Semmens, BC Stock, L Waterhouse, CM McCoy, B Johnson, D Heppell, S Barkdoll, S Huber, and S Heppell. 2022. Early Life History of Yellowfin Grouper (Mycteroperca venenosa) in Little Cayman, Cayman Islands. American Fisheries Society (AFS) 152nd Annual Meeting Conference Proceedings, presented 08/22/2022.

Early life history stages of fish have been shown to be sensitive to environmental changes. Given predicted changes in the coming century to the world’s tropical oceans, it is important to characterize how these changes will affect growth and survival of species with commercial and ecological importance. The Grouper Moon Project team has been conducting preliminary research on early life history of Yellowfin Grouper (Mycteroperca venenosa) with eggs and larvae collected from a Yellowfin Grouper spawning aggregation on Little Cayman, Cayman Islands, adjacent to the larger Nassau Grouper aggregation that is the primary focus of the Grouper Moon Project. Findings on Yellowfin Grouper growth and condition of eggs and larvae reared in varying temperature regimes was presented at the 2022 American Fisheries Society conference. From these baseline characterizations, we can inform future studies to better understand how a warming ocean will affect the species. Poster PDF

Wilson, KC, A Širović, BX Semmens, SR Gittings, CV Pattengill-Semmens, and C McCoy. 2022. Grouper Source Levels and Aggregation Dynamics Inferred from Passive Acoustic Localization at a Multispecies Spawning Site. The Journal of the Acoustical Society of America. 151, 3052;

As part of the Grouper Moon Project in Little Cayman, Cayman Island, this study used the sound produced by Nassau Grouper, Red Hind, Black Grouper, and Yellowfin Grouper to monitor the positions of these fish during the Nassau grouper spawning event that occurred in 2017. By using fish sound recorded by multiple instruments, we were able to monitor the presence and location of these fish before, during, and after the spawning. These continuous and overnight records added valuable observations to the limited period of times when divers are able to survey the area. Knowing the locations of the fish, it was possible to measure how loud these fish sounds are and determine how far they may be detected. The authors found that Nassau Grouper sounds were the loudest and may be detectable up to 300 m at this location. Additionally, the timing and locations of sound production suggest that there is no Nassau spawning events that occur during the night, but there may be overlap in space and time between Red Hind and Nassau Grouper spawning aggregations. View Online

Stock BC, Heppell SA, Waterhouse L, Dove IC, Pattengill-Semmens CV, McCoy CM, Bush PG, Ebanks-Petrie G, and Semmens BX. 2021. Pulse recruitment and recovery of Cayman Islands Nassau Grouper (Epinephelus striatus) spawning aggregations revealed by in situ length-frequency data. ICES Journal of Marine Science. doi:10.1093/icesjms/fsaa221

Fish usually need to be caught to be measured, but scientists from the Grouper Moon Project and Cayman Islands government have used video camera systems to collect an impressive 17-year dataset of Nassau Grouper lengths from Little Cayman. We combined this with information on growth and abundance to produce a comprehensive assessment of Nassau Grouper on Little Cayman. We found that Nassau Grouper recovered on Little Cayman largely thanks to one strong year class from 2011 spawning, 4-8x average. Length data from Cayman Brac also showed signs of a strong 2011 year class and substantial improvement in population status in recent years. Our analysis demonstrates that video camera systems are effective for monitoring protected fish spawning aggregations and are especially promising for situations where catch, effort, and invasive length data are unavailable. View Online

Blincow KM, Bush PG, Heppell SA, McCoy CM, Johnson BC, Pattengill-Semmens CV, Heppell SS, Stevens-McGeever SJ, Whaylen L, Luke K, Semmens BX. 2020. Spatial ecology of Nassau Grouper at home reef sites: Insights from tracking a large, long-lived epinephelid using acoustic telemetry across multiple years (2005-2008). Marine Ecology Progress Series (655): 199–214. doi:10.3354/meps13516.

Much of the science done by the Grouper Moon Project's collaborative research team is focused on gaining a better understanding Nassau Grouper populations in the Cayman Islands through studying their spawning aggregations; however, long-term acoustic tags (tracking pingers) allow us to gather information on how these fish behave at their home reefs outside of the spawning season. Nassau Grouper are known to be solitary and territorial. But during winter full moons, the fish leave their home site and travel, sometimes long distances, to a spawning aggregation, where they stay for up to 14 days. In this study, Grouper Moon scientists used tagging data to look at movement behavior and vertical habitat use. They found that most Nassau Grouper tend to return to the same home reef following spawning, but that the areas occupied at home reefs can change through time. In particular, they found that larger fish tend to occupy deeper areas than smaller fish, and fish will generally move to deeper reef areas over time. They also found that Nassau Grouper are more likely to be active at dawn and dusk than other times of the day, likely due to feeding activities. This information is adding to what we know about this iconic species, and will help support management of Nassau Grouper populations throughout the Caribbean. View PDF

Waterhouse, L, SA Heppell, CV Pattengill-Semmens, C McCoy, P Bush, BC Johnson, BX Semmens. 2020. Recovery of critically endangered Nassau grouper (Epinephelus striatus) in the Cayman Islands following targeted conservation actions. Proceedings of the National Academy of Sciences. Jan 2020, 201917132; doi:10.1073/pnas.1917132117.

This paper presents exciting results from the Grouper Moon Project, documenting conservation success for endangered Nassau Grouper. Results of the analysis showed that on both Little Cayman and Cayman Brac in the Cayman Islands, Nassau Grouper spawning aggregations have more than tripled in response to adaptive management by the Cayman Islands government over a decade. On Little Cayman, the aggregating population grew from around 1,200 fish in 2009 to over 7,000 in 2018. The study used a two-pronged approach that included tagging and video census data for monitoring and counting Nassau Grouper populations in an effort to more accurately estimate annual numbers of fish in the population, and thus provide insight into the effects of ongoing conservation efforts. While many governments have enacted regional or seasonal fishing closures in an attempt to allow recovery of overfished stocks of aggregating reef fishes, this is the first study to provide evidence that these measures can be successful across multiple decades. View PDF

Wilson, KC, BX Semmens, CV Pattengill-Semmens, C McCoy, A Širović. 2020. Potential for grouper acoustic competition and partitioning at a multispecies spawning site in Little Cayman, Cayman Islands. Marine Ecology Progress Series, 634: 127-146. doi:10.3354/meps13181.

This paper summarizes research done as part of the Grouper Moon Project to understand sound made by several species of grouper. Many fishes produce calls during spawning that aid in species and mate recognition. When multiple sound-producing species inhabit an area, the detection range may decrease and limit call function. Acoustic partitioning, the separation of calls in time, space, or spectral frequency, can minimize interference among species and provide information about fish behavior and ecology, including possible response to increasing anthropogenic noise. The authors investigated acoustic partitioning among 4 sound-producing epinephelids, Nassau Grouper Red Hind, Black Grouper, and Yellowfin Grouper, using passive acoustic data collected at the mass spawning aggregation site on the west end of Little Cayman in the Cayman Islands during the spawning seasons of 2015 to 2017. Results indicate separation in space and time between species calls, which aids in acoustic partitioning. When this separation did not occur, unique call structures were present, which may aid in effective intraspecies communication. View PDF

Wilson, KC, BX Semmens, SR Gittings, CV Pattengill-Semmens and A Širović. 2019. Development and evaluation of a passive acoustic localization method to monitor fish spawning aggregations and measure source levels. OCEANS 2019 MTS/IEEE SEATTLE, Seattle, WA, USA, 2019, pp. 1-7. doi: 10.23919/OCEANS40490.2019.8962663.

This work was presented at the OCEANS19 meeting, and was a result of research done as part of the Grouper Moon Project. More than 800 species of fish produce sound including Red Hind (Epinephelus guttatus), Nassau Grouper (E. striatus), Black Grouper (Mycteroperca bonaci), and Yellowfin Grouper (M. venenosa). Their sounds can be used to monitor these fish and may be a means to estimate abundance if parameters such as source levels, detection probabilities, and cue rates are known. During the week of Nassau Grouper spawning in February 2017, a passive acoustic array was deployed off Little Cayman in the Cayman Islands to study the temporal and spatial dynamics of spawning aggregations of Nassau Grouper and Red Hind, and measure the source levels of the sounds produced by all four species. The localization method was based on hyperbolic localization of cross-correlated time differences of arrival and its accuracy evaluated via simulations and empirical measurements. The high number of localizations at fish spawning aggregations suggests that localization can be used to accurately measure source levels, detection ranges, and other variables needed for density estimation of spawning aggregations. View paper online

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.

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

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 PDF

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 

Semmens BX, PG Bush, S Heppell, B Johnson, C McCoy, CV Pattengil-Semmens, and L Whaylen. 2007. Charting a Course for Nassau Grouper Recovery in the Caribbean: What We’ve Learned and What We Still Need to Know. 60th Gulf and Caribbean Fisheries Institute Meeting Proceedings.

Nassau Grouper (Epinephelus striatus) were historically one of the most important shallow water fisheries in the Caribbean, yet now are rarely taken. Although normally solitary, during the winter full moon Nassau grouper attend aggregations at spawning site to reproduce. Now, however, there are only a handful of known Nassau Grouper aggregations with more than 1,000 fish left in the Caribbean. Why has the species declined so precipitously, and what can be done to reverse the trend? These topics were explored during a presentation given by Grouper Moon researchers at the 2007 Gulf and Caribbean Fisheries Institute conference. The researchers presented recent and on-going research into the behavior and ecology of Nassau Grouper as part of the Grouper Moon Project, and highlight the conservation implications of this work. They also discussed critical research needs in the ongoing effort to identify prudent conservation measures for this species, including: habitat capacity, depensation, and recruitment variability. 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. 59th Gulf and Caribbean Fisheries Institute Meeting Proceedings. 59:1-14

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)

Taylor, JC, DB Eggleston, and PS Rand. 2006. Nassau grouper (Epinephelus striatus) spawning aggregations: hydroacoustic surveys and geostatistical analysis. NOAA Professional Paper. NMFS 5: 18-25.

In 2006, researchers from Univeristy of North Carolina Willmington collaborated with Grouper Moon Project researchers from REEF and Cayman Island Department of Environment to conduct mobile hydroacoustic surveys on the Little Cayman spawning aggregation site. Hydroacoustics, which is similar to a fish finder device found on a recreational fishing boat, but with better resolution and technology, has emerged as a valuable tool in fishery population assessments. The goal of the study was to determine the utility of this emerging technology to assist in the estimation of density, spatial extent, and total abundance of a Nassau grouper. This report summarizes the field effort and findings. View PDF

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