Grouper Moon Project

Latest update February 26, 2019 Started on November 21, 2018

We are working to conserve one of the last great aggregations of the iconic Nassau Grouper, a critically endangered reef fish.

November 21, 2018
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In The Field

The spawning has commenced! Last night at roughly 6:04 PM, our Grouper Moon team watched as the Nassau Grouper took off spawning. If you have ever observed grouper spawning through videos or in person, you might have compared it to watching fireworks explode- except instead of pops of bright lights it is gametes released into the water. As the females dart up in the water column they are followed closely by groups of males, who release their sperm as soon as the females release their eggs. The gametes then join together in the water column, and for the next 35-40 days drift about in the ocean before the survivors find their way back to the reefs. It is a technique that has worked for centuries for many fish species.

There is still much not known about Nassau Grouper spawning biology, and our team continues to explore these mysteries. Key data recorded over the last 17 years includes temperature of the water on the nights surrounding the mass spawning event. One of the most important trends our team has seen is that the spawning tends to occur when the water temperature is 27.2℃. These data indicate that the survival rate of juvenile Nassau Grouper could decline precipitously if global water temperatures increase their predicted 2-4℃ over the next 100 years. Dr. Alli Candelmo, REEF’s Invasive Species Program Manager and Dr. Scott Heppell, Associate Professor of Fisheries at Oregon State University, have been collecting eggs in order to determine how developing embryos and larvae may be affected by increased temperatures, UV light, and salinity. Overall we hope these experiments will give us a good understanding of how populations will react to a changing climate.

In the short clip below you can watch as Dr. Candelmo uses an integrated tow to collect eggs during the spawning event last night. The developing embryos are currently back in our hotel room laboratory where we continue our temperature and UV light experiments.

As part of each of REEF’s projects we include an education component in order to connect the general public to our conservation efforts. In 2012, the Grouper Moon Project partnered with Disney Worldwide Conservation Program in order to develop an education component to the research occuring in the Cayman Islands. Over the years, this program has reached 18 schools in the Cayman Islands, Florida, Bahamas, and Turks and Caicos, reaching roughly 1400 students. The Grouper Education Program is a great way to share our research, as well as educate young students on the social, ecological, and economic facets of Nassau Grouper.

There are two components included in the Grouper Education Program - classroom lessons and live-from-the-field chats. Prior to the spawning event, teachers use a REEF-created curriculum that teaches the students about coral reef ecology, the Nassau Grouper’s biology, and its history in the Cayman Islands and wider Caribbean. As the winter full moon approaches, students are eager for the scientists to arrive so they can observe and ask questions.

Once the official Grouper Moon field season begins, students have the opportunity to tune in to interactive live-feeds over the 10 days. During these hour-long broadcasts, students listen to stories about the project, watch interviews with project scientists, and experience live underwater footage as they are guided through a dive. In addition, students have the opportunity to ask the scientists and volunteers questions. “Our education program culminates in these incredible, live-from-the-field, video conferences between students and the scientists and researchers on Little Cayman. In this way, we are able to bring real-life field science right into the classroom. It is an incredibly effective way to engage students and help facilitate a deeper understanding and connection with the Nassau Grouper, and ultimately the entire reef ecosystem,” says REEF’s Grouper Moon Education Coordinator, Todd B. These live feeds are not just for students however, anyone can tune into these live feeds by watching our YouTube channel “REEF Grouper Moon Project.”

In the coming years, REEF hopes to expand the project to more schools in Florida and beyond, as well as incorporate more training and support for participating teachers. “We have found that providing ample resources for educators in the classroom is paramount to our program’s success. So, next year we are planning to facilitate professional development workshops to help provide this support. We are also hoping to package the lesson plans in to a more formal curriculum,” says lead scientist Dr. Christy Pattengill-Semmens. For now students and general audiences interested in the project can check out our YouTube channel or follow our blog and social media. See

Majority of the team has made it back to Little Cayman! We are excited to get back into the water tomorrow and see what the Nassau Grouper have been doing since last month. Will our predictions of larger group size be correct? While unsure today, the team is preparing for increased number from the 2,000 individuals last month.

In hopes of more Nassau Grouper, our team has increased from six to sixteen. In addition to the research on Little Cayman, we also plan to visit Cayman Brac in pursuit of exploring additional spawning sites.

Our trip will not only be packed with science, but we are excited to share our experience with local Caymanian and Florida classrooms through live stream education lectures. These classes provide the opportunity to “meet the scientist” and see what is occurring “live from the field.”

Today our team kicked off this month of Grouper Moon with our first live stream class of the year. Lead scientists Dr. Brice Semmens, Ph.D. and Dr. Christy Pattengill-Semmens, Ph.D. discusses the biology of Nassau Grouper, and the importance of this study. Below you can find the video of today’s interview. You can catch previous recordings any time by visiting our YouTube channel “REEF Grouper Moon Project.”

Looks like a great project! Protecting spawning aggregations is so important to ensure the long term survival of a species. Please check out our black bream project in the UK where the species is exploited during its most vulnerable spawning period - we are trying to educate people about what happens during spawning and nesting.

Do you ever film the groupers at night? If so, what cameras do you use?

Our bags are packed and we are heading back to the states for a couple weeks of work and prep. We made some interesting observations this trip and are eagerly awaiting our return in February to continue the research. The largest number of individual Nassau grouper we estimated this January was roughly 2,000 individuals. However, our team expects the rest of the population to arrive in February for a big spawning event after the next full moon. This month gave us a great opportunity to collect some early data on individual fish and sizes at the site as well as explore other locations on the island.

In February, we predict the number of Nassau grouper will be even larger as new adults continue aggregate at the spawning site. Our team of scientist will double for the next month in anticipation of the big spawning event. We will be busy with a number of research components; including tagging, length assessments, fish face imaging, Trident ROV surveys and egg collection and buoyancy studies (stay tuned for future blog posts for explanations of this research).

For now, we wave goodbye to the Nassau grouper with the comfort that we will return to Little Cayman in just a few weeks to continue to build upon our understanding of the population dynamics and conservation of this charismatic fish species.

The weather took another turn this morning. We woke up to a surprise of monstrous 6-8 foot waves coming from the east, making it impossible for the team to make it out early. Why? -- boats are kept in safe harbor in a back bay formed by a barrier reef along the southeast side of the island. This bay has a few smalll “cuts”, or breaks in the barrier reef sufficiently large for boats to get out of the calm back bay waters. However, in rough conditions it can be difficult and potentially dangerous to navigate through these cuts. This was the case this morning.

After the winds calmed a bit this afternoon, and the boat could safely navigate the cut, the team attempted a dive at the aggregation site. However, after a torturous trip over persistent high seas, it became clear that conditions were not safe enough to get into the water. To give you a visual of the conditions, we have created a short video for you all to see (below).

For now, as we sit and wait for the weather to pass, we are curious if the grouper did spawn over these last couple of days, or will next month be the big event? Let’s hope we can make it out this evening to see.

Up through this morning, our scientists have only seen a few hundred Nassau grouper at the spawning site. But this evening, things changed. The stormy weather finally subsided, allowing our team to visit at sunset. It is critical for our divers to get in the water in the late evening because spawning occurs at that time. Unlike previous days, tonight we were treated to the welcome sight of nearly 2,000 individual grouper gathered together.

While 2,000 fish sounds like a large number of Nassau grouper, just last year our team documented close to 7,000 individuals present for the mass spawning event. Why are there fewer fish this January? Nassau grouper spawning is driven by lunar cycles, meaning they depend on the moon to determine when spawning should occur. Typically Nassau grouper aggregate to spawn in either January or February depending on the date of the full moon. Our research has demonstrated that should the full moon fall late in January, the large mass spawning will occur in that month. However, if the full moon is in early January, the large number of individuals will not aggregate to spawn until February. This year it was difficult to determine when the mass spawning would occur because the moon fell near mid-January, causing our team to wonder if the Nassau grouper would spawn this month or next. Due to the current number of individuals, the Grouper Moon team believes there may be some spawning this month, but expect to see an even larger group in February.

The presence of 7,000 of these endangered grouper last year, and the prospect of even more this coming February, is really exciting for our team. Could this mean that populations are recovering from the critically endangered status they currently hold? It is still too early to tell. Just this year the Nassau grouper was designated as critically endangered by the International Union for the Conservation of Nature (IUCN). So while there is much good news for Cayman, the news is poor across the Caribbean, and our research on Little Cayman is more critical than ever.

Regardless, 2,000 fish was a welcome sight for our team. We will continue tracking numbers for a few more days, will watch for potential spawning, and plan to return next month for the big event. Stay tuned for more Grouper Moon news by following our blog or visit for more information on the background and history of the project.

*Photo Credit Janna Nichols


The Grouper Moon team has been very busy the last few days trying to keep track of Nassau Grouper populations on Little Cayman. In previous years we have seen aggregations of thousands on the very western end of the island (the known spawning site for the species in recent years). This year, however, we have not been able to spot groups this large, causing us to wonder if they will actually spawn this month.

Many decades ago, Nassau grouper used to spawn on the very EASTERN end of the island. Could it be that the growing population of grouper on the island has, just this year, shifted to spawning at the historic east end site? To test this theory, our team of divers spent the last two days exploring this old spawning site in an effort to find the missing spawners – with very little success.

The search continues…

Given the relatively few grouper at the spawning site in comparison to years past, it is still unclear if the spawning will happen this month or next. We can report, however, that so far there are many fewer Nassau Grouper at the traditional locations than expected. We will continue our search tomorrow, as the seas calm and the wind dies. Fair weather ahead!


The weather finally calmed a bit this morning allowing the Grouper Moon team to get back into the water. While excited to see what the Nassau Grouper were up to, we were thankful to have the day yesterday to test our skills with the Trident ROV. On a pier overlooking Owens Island, we took turns maneuvering the ROV across shallow sea grass beds, hoping to perfect our skills before taking it to the deeper reef sites. We hope later this week will be able take it on the boat and get some great footage of the grouper aggregations.

As we hit the water today in hopes of seeing the grouper spawning, we were surprised to see only about 300 individuals at the traditional Little Cayman aggregation site. While this may sound like many Nassau Groupers in one area, last year’s spawning season brought in more than 6000. Maybe this is a sign that they will not be spawning until next month? Stay tuned to find out.

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A storm from the North has rolled in over night, bringing with it strong winds and high seas. Our team is currently not able to get out to the aggregation site, and are thus in a holding pattern; taking the time to check and re-check equipment, sorting out camera issues, and using this opportunity to test our Trident ROV in the calm waters of a nearby pool. We are hoping the seas will calm by tomorrow evening.

Meanwhile, we are left to wonder what the Nassau grouper are up to out at the aggregation site. Will January be the big spawning month? Or will it be February? In most years, we know in advance when the fish will spawn -- in years when January has a late full moon, the grouper will spawn in Late January. In years when the full moon is early in February, the grouper will spawn shortly thereafter. This year, however, the full moons fall towards the middle of both months. Rather than guessing when they will spawn, our team will field research teams in both months.

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Grouper Moon 2019 has officially begun. This year marks the 18th year of this long-term monitoring program, jointly run by the Cayman Islands Department of Environment (CIDOE) and Reef Environmental Education Foundation (REEF). The aim of the program is to monitor fish spawning aggregations in the Cayman Islands, with a focus on the iconic Nassau Grouper, a critically endangered reef fish species in the Caribbean.

Each year, we monitor the spawning behaviors in reef fishes during the winter spawning season. In the last year, our researchers identified some potential new multi-species spawning sites on Little Cayman. We intend to explore these sites using our new Trident ROV off of a CIDOE research vessel. But first, we need to learn how to deploy and drive the ROV! This is our first great adventure in the Caymans this year, and we intend to bring you along as we progress with our new technology.

Stay tuned for more photos and videos from the Grouper Moon Project. Also, check out REEF’s Instagram and Facebook Pages or visit to stay up to date with all Grouper Moon Project news.

Here's a picture of the full moon rising over South Hole Sound on Little Cayman last night. Enjoy!


In addition to our work on the endangered Nassau Grouper, Grouper Moon Project scientists also study the other fish species that use this site to spawn. Expedition Leader, Dr. Brice Semmens, recently presented initial findings from acoustic tagging work on Tiger Grouper at the Gulf and Caribbean Fisheries Institute conference in San Andres Colombia, November 2018. Read more here:

Photo: A Tiger Grouper with an acoustic tracking tag externally attached. These tags help scientists look at the home range and movement activities of species. Similar technology has been used for the Nassau Grouper on Little Cayman. Photo by Guy Harvey.

Expedition Background

Each winter, our team mounts an expedition to Little Cayman to collect data in support of effective fisheries management for the critically endangered Nassau grouper. The expeditions involve exploration dives, ROV survey of fish spawning aggregations, and advanced oceanographic survey methods (e.g. surveying eggs and larvae using underwater microscopes).


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