The Grouper Moon Project

A collaborative conservation program between REEF and the Cayman Islands Department of the Environment studying Nassau grouper (Epinephelus striatus) - a social and ecological corner stone of Caribbean's coral reefs.

Exciting News (August 2016): Grouper Moon findings lead to sweeping science-based protections for Nassau Grouper in the Cayman Islands! Read More Here.

Resources | What are Nassau Grouper? | Grouper Moon Project Overview | Yearly Project Summaries | Published Results | Videos |Collaborative Team and Supporters



What are Nassau Grouper?

Normally solitary and territorial, during the winter full moons grouper travel, sometimes over great distances, and “group” together to spawn. About fifty of these spawning aggregations sites have been recorded in different places throughout the Caribbean. Historically, once discovered, grouper aggregation sites have become synonymous with fisherman aggregation sites. Due to the timing and site fidelity of the spawning aggregations and the ease with which these relative loners can be caught while congregating by the hundreds and thousands to spawn, one-third to one-half of the known Caribbean aggregation sites are now inactive. The Cayman Islands used to be home to five Nassau grouper (Epinephelus striatus) spawning sites. Today, four of these sites are dormant or depleted. But one site, on the west end of Little Cayman Island, is home to one of the last great reproductive populations of this endangered species.





Grouper Moon Project Overview

Photo by Paul Humann
In the Winter of 2002, REEF launched a ground breaking expedition to the Cayman Islands - the Grouper Moon Project. The Project’s objectives were to observe the Nassau grouper spawning aggregation off the western tip of Little Cayman, and to develop a protocol for monitoring their numbers and activity at the site. For two weeks, a team of divers from REEF and the Cayman Islands Department of Environment visited the aggregation site and nearby reefs. Since that first year, REEF has coordinated annual efforts to monitor and study the Little Cayman Nassau grouper aggregation. The project has grown in scope to include an ambitious acoustic tagging research project, juvenile habitat and genetics studies, and early results have been published in the scientific literature. Components of the project include:


Nassau Grouper: A Caribbean Icon, Education Program - In the Fall 2011, REEF and our collaborators started development of an education program that will coincide with the Grouper Moon Project. Working with a professional educator, the program includes curricular materials and classroom lessons, as well as "meet the scientist" and "live from the field" sessions. Working in collaboration with classrooms from Cayman Prep and High School, and with funding from the Disney Worldwide Conservation Program, we piloted the program during the aggregation field season in 2012. To view a short clip of the underwater live-link, showing project scientist Dr. Brice Semmens answering qustions from students while underwater, click here. To find out more about this program, visit the Grouper Education Project EduBlog. You can also watch archived underwater Live-Feeds.

Baby Grouper Adrift! - Satellite Drifter Project - Spawning aggregations are typically located at promontories that feature a confluence of currents and waves. Why there? Using satellite drifters, we are studying the passive transport of Nassau grouper larvae spawned at the protected aggregation sites in the Cayman Islands to better understand the importance of place. This research is funded by the Disney Worldwide Conservation Program. To visit the 2011 Baby Grouper Adrift! webpage, click here.

Marine Protected Areas and Spawning Aggregations - Starting in 2008, REEF and our collaborators at the Cayman Islands Department of the Environment (CIDOE) and Oregon State University (OSU) greatly expanded the conservation science research being conducted as part of the Grouper Moon Project in the Cayman Islands. The funded research, broadly titled as "The reproductive biology of remnant Nassau grouper stocks: implications for Cayman Islands Marine Protected Area (MPA) management" aims to evaluate the potential for spawning site MPAs to recover Nassau grouper stocks. This research was funded by a grant from the Lenfest Ocean Program at the Pew Charitable Trusts and expanded on the initial findings of the Acoustic Research Project that was started in 2003.

Acoustic Research Project - In 2003 the Cayman Island Marine Conservation Board instituted an 8-year total fishing ban on all known Nassau grouper (Epinephelus striatus) aggregation sites in the Cayman Islands.This project was conducted to provide a clearer understand of how local populations of Nassau grouper use aggregation sites, to evaluate the effect of the no-take status of aggregation sites, and in order to assess the likelihood that the closures are effective. We acoustically tagged Nassau grouper both on and off the Little Cayman west end aggregation site, and monitored movements of the tagged fish over a two year period using an array of passive autonomous hydrophones surrounding the island. This work was funded by the NOAA International Coral Reef Conservation Program. For more information, results, and to watch videos of Nassau grouper movement to and from the aggregation, click here.

Photo by Jim Hellemn

Yearly Project Summaries

Click here to read annual summaries of the Grouper Moon research.


Published Results

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
Observations of a Nassau Grouper (Epinephelus striatus) Spawning Aggregation Site In Little Cayman, Including Multi-Species Spawning Information. 2004. 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


Click on the title to view/download the video. Formats and sizes vary, see end of description for details.

2013 Spawning Night Compilation - Watch this short video montage of the aggregation and spawning action in February 2013.

Changing Seas: Grouper Moon - This episode of the Emmy award-winning "Changing Seas" PBS series features the story of the Grouper Moon Project. It features interviews with scientists, information about the cutting-edge research being conducted, REEF's education and outreach efforts, and spectacular underwater footage.

Grouper Education Program Underwater Live Feed Highlights - As part of the Grouper Education Program, our team conducts "live from the field" sessions. In this video, Professor Brice Semmens of the Scripps Institution of Oceanography chats live from underwater with students from Cayman Prep and High School during the 2012 research field season.

Grouper's Last Stand - A 3-minute PSA highlighting the importance of protecting spawning aggregations. This video was produced in 2011 by Josh Stewart in the month's leading up to the expriation of the original 8-year ban on fishing at aggregation sites durign spawning in the Cayman Islands. Thanks to awareness raised by this PSA and other Grouper Moon outreach efforts, the Cayman Islands Marine Conservation Board exteded the ban for another 8 years in December 2011. (YouTube)

2012 Spawning Highlghts - A short video featuring field work from the 2012 Grouper Moon season. (YouTube)

Grouper Moon Project Documentary - A 16 minute documentary video produced by Dr. Brice Semmens in 2006 that highlights REEF's collaboration with the Cayman Islands Department of the Environment on this critical conservation science project. The acoustic tagging research that was initiated in 2005 is featured. (Windows Media Player, 33 MB).

Cleaning Station at the Aggregation - During the February 2006 aggregation, we placed stationary cameras on two active cleaning stations for one hour intervals during the day in order to record behavior and cleaning station activity. A compilation of time-lapse video from a cleaning station, sped up 2x actual speed, -- the video represents approximately 10 minutes over two days at one large sponge that served as an active cleaning station on the Little Cayman West End aggregation site. The Nassau grouper are seen flashing various colorations during their attempts to be in the primary cleaning location in the sponge. In addition to Nassau grouper, yellowfin grouper and tiger grouper occasionally show up to be cleaned (but rarely are allowed access for more than a few moments). (Windows Media Player, 12 MB) 

Little Cayman Spawning Aggregation Compilation 2008 - This video is a compilation of activity at the West End Little Cayman spawning site. The clip features the large number of Nassau grouper at the site (estimated at 3,000-3,500 individuals) a few days prior to spawning, the use of the site by many different species to spawn (including horse-eye jack), Caribbean reef sharks that try to prey on spawning (and distracted!) fish, and finally the big event, Nassau grouper spawning. (Windows Media Player, 20MB) 

Grouper Moon 2008 Compilation - This video/audio compilation was edited by Dr. Scott Heppell (OSU) and features topside and underwater footage of the January 2008 field research. (Windows Media Player, 50MB)

Current Drifter Tracks - Three satellite drifters were deployed at the Little Cayman aggregation site on the night of spawning. The paths will be recorded by ARGOS satellites for 45 days and the resulting data will be used to develop a larval dispersal model in collaboration with researchers from University of Miami. Little Cayman is the island shown. The video represents movement between 1/29/08 and 2/11/08. See the 2008 Project Summary for more information on this work. (AVI, 10MB)

Fish Movement - Preliminary results from the acoustic tagging project that was initiated on Little Cayman in 2005 to understand the movement patterns of Nassau grouper. This link will take you to a page with links to movement track videos of all tagged Nassau grouper.

Acoustic Tagging Methods - This link will take you to a page with several short video clips of the capture, tagging, release, and tracking methods used in the Grouper Moon Acoustic project.

2002 Little Cayman Spawning Aggregation - A short compilation of video from the first year of video documentation of the Little Cayman West End Aggregation Site in 2002. Footage includes daytime behaviors and spawning releases. (Windows Media Player, 10MB).

All videos, images and content from these pages are copyrighted by REEF/Grouper Moon Project. Viewing and/or downloading any content implies agreement to the terms of use. Appropriate photo/video credit and copyright information must be given and notification of their use must be provided to REEF.

Collaborative Team and Major Supporters

The Grouper Moon Project is a collaboration between REEF and the Cayman Islands Department of the Environment. REEF extends a huge thanks to the CIDOE staff for their tireless efforts, including Phil Bush, Bradley Johnson, Croy McCoy, James Gibb, Tim Austin, Gina Ebanks-Pietre, Keith Neale, Delwin McLaughlin, and Robert Walton. The Grouper Moon Project has continued through the years empowered by the first year’s success and the passion of project leader Leslie Whaylen Clift.

REEF volunteer project team members have included: Judie Clee, Thor Dunmire, Heather George, Dr. Steve Gittings, Tracey Griffin, Doug Harder, Brenda Hitt, Doug Kessling, Denise Mizell, Hal Peterson, Alex Score, Sheryl Shea, and Leslie Whaylen Clift. Drs. Scott and Selina Heppell from Oregon State University have been assisting with various Grouper Moon research projects since 2005. The 2010 Our World Underwater Scholar, Josh Stewart, has assisted with field efforts and outreach since in 2011 (as a Scripps Inst. of Oceanography graduate student since 2012). OSU graduate student, Stephanie Kraft-Archer assisted the project 2008-2011. Scripps Inst. of Oceanography graduate students, Brian Stock and Lynn Waterhouse, have assisted with field efforts and data management in since 2012.

Generous logistical support has been provided throughout the years by Peter Hillenbrand, as well as by local dive operators at the Little Cayman Beach Resort/Reef Divers and the Southern Cross Club. Brac Reef Resort has provided lodging support for education efforts on Cayman Brac. Cayman Airways has provided inter-island travel support. Grants from the Disney Conservation Fund, beginning in 2011, have supported field efforts, the Baby Grouper Adrift webpage, several outreach products, and the development and continued coordination of the Grouper Education Program. A research grant from the Lenfest Ocean Program at the Pew Charitable Trusts funded the project between 2008-2011. Funding for the acoustic work was provided in 2009-2012 by the NOAA International Coral Reef Conservation Program, the J. Edward Mahoney Foundation, and PADI Project AWARE. Additional funding has been provided by hundreds of REEF members. Wayne Sullivan and his crew of the Glen Ellen has provided generous field support since 2009. Raymarine Marine Electronics donated RADAR equipment to assist the CIDOE in their enforcement efforts. To alleviate the constraints of diving deep depths on regular scuba, several other sponsors came on board to assist in the project, including Divetech and PM Gas of Grand Cayman, Silent Diving of Brockville, Ontario and Shearwater Research of Vancouver, British Columbia. FLOW Cayman Islands (previously LIME) has provided 4G internet support for the live-video feeds for the Grouper Education Project since 2012, and Ocean Reef Systems and Ocean Systems, Inc. have provided technical support for the live feeds. Pegasus Thrusters supported the project in 2013 through the donation of Diver Propulsion Vehicles. Cayman Airways has provided travel support, and McLauglin Car & Scooter Rental has provided island transportion on Little Cayman.