Every winter, during the full moon, something extraordinary happens beneath the waves in the Cayman Islands. Grouping together by the thousands, at specific locations, the iconic Nassau grouper (Epinephelus striatus), gather to reproduce. What makes this spectacle so remarkable is that Nassau groupers are normally a solitary, territorial, top reef predator spending the majority of the year alone on their patch of the reef, but during the first full moons of each year, they make an incredible journey to known aggregation sites to “group” together with their fellow partners to spawn future generations.
Historically, around fifty spawning aggregation sites have been documented throughout the Caribbean, but tragically, once discovered, the sites would become subjected to intense fishing pressure. It is estimated that one-third to one-half of the known Nassau grouper aggregation sites in the Caribbean are now no longer viable due with too few fish as a result of overfishing.
The Cayman Islands was once home to five commonly known Nassau grouper spawning sites but like other aggregations across the region, fishing pressure eventually rendered them severely depleted or completely dormant. In the late 1980’s Cayman fisherfolk, noticing the dwindling catch and smaller fish approached the Department of Environment (DoE) to voice their concerns. DoE scientists immediately began collecting data to better understand the issue, looking closely at catch per unit effort and the size of the fish being extracted. There was clear evidence the fishery was being exploited at unsustainable harvest rates. Management recommendations were proffered, but went largely unheeded.
The Cayman Islands was once home to five commonly known Nassau grouper spawning sites but like other aggregations across the region, fishing pressure eventually rendered them severely depleted or completely dormant. In the late 1980’s Cayman fisherfolk, noticing the dwindling catch and smaller fish approached the Department of Environment (DoE) to voice their concerns. DoE scientists immediately began collecting data to better understand the issue, looking closely at catch per unit effort and the size of the fish being extracted. There was clear evidence the fishery was being exploited at unsustainable harvest rates. Management recommendations were proffered, but went largely unheeded.
Then in 2001, a truly active aggregation site of around six thousand Nassau grouper individuals was rediscovered in the deep waters off the west end of Little Cayman. Word quickly spread and fishers flocked to the site and, fishing intensively, removed around four thousand fish over two years diminishing two thirds of the original estimated numbers. Not only had the aggregation site been severely depleted but many of the harvested fish were wasted as a result of the flooded market. In response, the then Marine Conservation Board immediately established a temporary eight-year ban on fishing known grouper aggregation sites, as 8 years is the average length of time for Nassau grouper to reach reproductive maturity and join the aggregation. It was hoped the 2003 ban would relieve the fishing pressure and give the population a chance to replenish while scientific teams ramped up research to understand how the species was being impacted and what management interventions were needed.
To assist with the increased monitoring and research requirements of what had been determined as the last substantially active Nassau grouper spawning aggregation in the Caribbean, DoE partnered with the Reef Environmental Education Foundation (REEF) whose network of volunteers and scientists from Scripps and Oregon State University, mobilized to form the Grouper Moon Project in 2002. Their focus was to more accurately determine how many grouper were attending the aggregation and assess if and how restricting the fishery would benefit the population over time. Since then, both scientists and grouper alike travel to the west end of Little Cayman every winter to experience and document the last great reproductive population of this critical keystone species.
Grouper spawning is highly tuned to the celestial moon cues, and takes place on just a few nights during the week following one the full moons in January, February or sometimes March. Like most fish aggregation hotspots, the Little Cayman spawning site is about 100 feet deep in tumultuous waters exposed to strong offshore currents. It is still unknown how the fish know when to gather or even when to spawn but studies suggest there is a strong connection to the strength and directions that currents are flowing, with spawning frequently occurring on nights when currents are creating gyres of circulating water which vastly improves fertilization as eggs and sperm are literally mixed together before being carried to the relative safety offshore.
Over the years, many cutting edge innovative techniques have been employed to assist in the research of this remarkable species, including fish tagging, acoustic monitoring, sonar, spatial video, satellite drift tracking, and even AI facial recognition technology. Another important aspect of the Grouper Moon Project is the extensive education component which offers incredible underwater live stream views and even interviews with REEF scientists in real time while they are diving the aggregation site. Schools across the Cayman Islands and the USA tune in to ask questions directly to the scientific team to get a first-hand look at what they working on and see the awe inspiring aggregation for themselves.
Recognising and understanding the significance of these natural treasures, regulations officially closing all spawning aggregation sites to fishing were passed into law in 2012 and carried into the National Conservation Act when it was enacted in 2013. Sustainable fishing practices now allow Nassau grouper to remain open to fishing outside of the marine protected areas with catch and size limits from May 1st through November 30th while the closed season prohibits the taking of Nassau grouper anywhere in Cayman waters during spawning December 1st through April 30th. This firm and deliberate legislative support exemplifies how even the very best research cannot actualize successful conservation without a unified strategy.
The Grouper Moon Project represents a crowning example of the power of collaboration, long-term data collection, appropriate management recommendations, community support and effective enforcement leading to meaningful and significant conservation success. However, even with the local grouper population having tripled in size in the last 30 years, there is still a long way to go considering spawning aggregation sites used to see tens or possibly even hundreds of thousands of fish. Though we are unlikely to ever see those numbers again, it is encouraging to see the persistence and dedication to research and management by both the Department of Environment and REEF marine science teams continue to flourish in this rare example of a successful species recovery.
Learn more at
https://doe.ky/grouper
https://www.reef.org/programs/grouper-moon-project
Watch the documentaries!
It’s one of the most iconic fish in the Caribbean: The Nassau Grouper. For the first time online, Dr. Guy Harvey presents the incredible long-term work underway in the Cayman Islands to protect the Nassau Grouper. Along the way, you’ll meet passionate scientists from REEF.org and Oregon State University eagerly working with the Cayman Islands government to turn the tide for this species. You’ll even find out why Sir Richard Branson is taking part. Jump in to help save a species, right now on Guy Harvey Expeditions.
Produced by PBS /ChangingSeasTV
Join researchers from the Reef Environmental Education Foundation (REEF) and the Cayman Islands Department of Environment as they study one of the last great reproductive populations of Nassau Grouper. Normally a solitary species, during the winter full moons Nassau Grouper travel, sometimes over great distances, to “group” together and spawn. While most of the known spawning sites in the Caribbean have been fished out over the years, the west end of Little Cayman in the Cayman Islands is home to largest known reproductive spawning aggregation of this endangered species.