Nassau Grouper populations increased threefold in response to dynamic fishing management actions in the Cayman Islands

A new study from the Grouper Moon Project has documented a successful recovery effort among Nassau Grouper populations in the Cayman Islands. It also highlights the value of collaborative efforts for conservation success.

The study, published January 6, 2020, in Proceedings of the National Academy of Sciences, 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.

“Normally, Nassau Grouper are relatively solitary, and tend to be hard to catch,” said Lynn Waterhouse, a Grouper Moon scientist. “But at spawning, they come together en masse to form annual spawning aggregations, where historically tens of thousands of fish come together to reproduce, so they’re very easy for fishermen to catch.”

Due to overfishing during spawning, the species has suffered region-wide stock collapse. By the 1980s large aggregations had all but disappeared from the Caribbean region. Of the remaining aggregations, few contained more than 1,000 individuals and the species is currently listed as critically endangered by the International Union for Conservation of Nature.

In 2001, an aggregation of around 7,000 Nassau Grouper was discovered by fishermen near Little Cayman, the smallest of the three islands located south of Cuba in the Caribbean Sea. The subsequent rapid overfishing of the aggregation drove the Cayman Islands Government to ban fishing at aggregation sites during the spawning season beginning in 2003. During this time, Reef Environmental Education Foundation (REEF), a non-profit marine conservation organization, launched the Grouper Moon Project in partnership with the Cayman Islands Department of Environment (CIDOE), to develop a monitoring strategy for the remaining Cayman Island aggregations. Researchers from Scripps Institution of Oceanography and Oregon State University have since joined the effort.

The Grouper Moon Project represents nearly 20 years of research, monitoring, and outreach efforts. It 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.

“We developed a unique approach for monitoring these populations over the course of nearly two decades,” said senior author Brice Semmens, an associate professor and ecologist at Scripps Oceanography. “This included a combination of using mark and recapture tagging techniques to track the proportion of tagged fish and video transects to count aggregating fish.” The researchers faced a number of obstacles, including funding challenges and particularly difficult ocean conditions – the Nassau Grouper has the unfortunate habit of aggregating at inconvenient and often dangerous locations along the reef shelf edge, making it difficult for divers to easily access the aggregation. But with the support of the CIDOE, the team has maintained their monitoring efforts for over 15 years.

Importantly, the researchers did not just track the number of fish in the aggregation – they worked together with the CIDOE and local communities to share results and discuss next steps. After reviewing the data being collected by the Grouper Moon Project in 2016, the government initiated an even more progressive fishing policy, banning all fishing of Nassau Grouper during the winter spawning season along with limits on the number and size of fish that can be kept.

As a result, the Nassau Grouper population have more than tripled in response to adaptive management by the Cayman Islands government. On Little Cayman, the aggregating population grew from around 1,200 fish in 2009 to over 7,000 in 2018. This study is the first to show sustained recovery of Nassau Grouper populations following fisheries-induced collapse.

“This really demonstrates the power of this collaborative and adaptive approach to conservation,” said co-author Christy Pattengill-Semmens, REEF’s Director of Science. “We were able to monitor the population and provide information to support management as the data came in, allowing the Cayman government to respond rapidly with policy changes.”

“These efforts have been successful because of the strength of the partnerships among the government, academic research groups, and nonprofits,” she added. “CIDOE also has a long history of working with fishing communities in the islands, and the fishers’ compliance and support has been key to this conservation success.”

The team also emphasized that these results show that patience is key.

“Due to the way these fish breed and the timing and location of spawning events, it can take several generations before the right ocean conditions ultimately facilitate young grouper joining an aggregation,” said Pattengill-Semmens. “This means that communities and governments may need to implement protection strategies over the course of years or even decades to meet their management targets.”

“The Grouper Moon Project provides a model for conservation success that holds promise for a region wide recovery for this critically endangered species, and is an ideal approach for conservation,” said Semmens. “Just doing the science isn’t enough. You need to partner with groups and governments capable of turning science into conservation decisions that support the local community.”

Additional co-authors include Scott A. Heppell of Oregon State University; Phillippe Bush and Bradley C. Johnson of the Cayman Islands Government Department of Environment; and Croy McCoy of the Cayman Islands Government Department of Environment and Bangor University.

This research was funded in part by the Lenfest Ocean Program, the Disney Conservation Fund, the NOAA International Coral Reef Conservation Program (Grant NA04NOS4630287), P. Hillenbrand, the J. Edward Mahoney Foundation, the Sea Grant and NMFS fellowship NA13OAR4170110 E/PD-11 and the PEO Scholar Award.

The open access paper is available online here:

Recovery of critically endangered Nassau grouper (Epinephelus striatus) in the Cayman Islands following targeted conservation actions. Lynn Waterhouse, Scott A. Heppell, Christy V. Pattengill-Semmens, Croy McCoy, Phillippe Bush, Bradley C. Johnson, Brice X. Semmens. Proceedings of the National Academy of Sciences Jan 2020, 201917132; DOI: 10.1073/pnas.1917132117