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Grouper Moon scientists expand focus beyond Nassau

Scientists on the Grouper Moon project collected a photo of this Nassau grouper for use with a facial recognition program.

For more than 15 years, The Department of Environment has partnered with scientists from REEF to protect a Caribbean icon: the Nassau Grouper. In that time, the Grouper Moon project, as it’s known, has expanded its research to include other grouper species.

The spectacle of the annual reproductive rites of the Nassau grouper make it arguably the headline act of the long-running Grouper Moon research project. Over the last decade in particular, scientists have watched the Nassau grouper population at Little Cayman’s West End spawning aggregation more than triple in the last ten years. It’s now estimated to be upwards of 7,000 individuals.

After four intense nights of spawning, the Nassau grouper take a well deserved rest, and the spawning grounds are taken over by other species like the tiger grouper and yellowfin grouper. Now, Grouper Moon project scientists are now studying them too.

Cayman 27’s cameras were welcomed aboard the DOE’s RV Sea Keeper last week. The mission: to tag 20 yellowfin grouper with acoustic tracking devices.

It’s been said that a bad day of fishing is better than a good day at the office.

“It is never easy work, but it’s always fun work,” said Dr. Scott Heppell of Oregon State University, one of the scientists on the long-running Grouper Moon project. “It’s the same as when you’re doing science as when you’re out there for fun, sometimes you get exactly what you’re after, and sometimes you don’t.”

Seawater flows over the fish’s gills while blood and tissue samples are gathered by the Grouper Moon team

But this fishing trip, while pleasurable, is more than just for kicks. Dr. Heppell explained the day’s primary objective.

“We’re trying to catch the yellowfin grouper to implant acoustic tags in them so we can look at their movement patterns around the island, how they use different habitats at different times a year, and with their aggregation behavior is like,” said Dr. Heppell.

When a specimin is hooked, the research team springs into action to collect the data they need.

“We bring it up, we get it on the boat, we measure its length, we put it in a cradle to keep it safe, we put water over it’s gills, and then we take our tissue samples, our blood samples,” said Dr. Heppell.

Instead of a yellowfin, a Nassau grouper is on the line. Though it wasn’t what they were looking for, Dr. Heppell said it is still useful to the Grouper Moon team.

A recompression device is used to assist the grouper’s return to depth

“We were able to get some samples out of a couple Nassau grouper that we caught today,” he said. “We will analyze the hormones for testosterone and estrogen, basically so we can tell the sex of the individuals.”

Each crew member executes his or her role fluidly and with precision, resembling somewhat the work of a pit crew in auto racing.

“We want to get it back in the water, but not just in the water, back to the bottom as quickly as possible,” said Dr. Heppell.

The fish is released to the water, but there’s a problem. Even with the aid of a recompression device, it can’t stay down.

Dr. Brice Semmens leapped into the water to haul the Nassau grouper in for another try, this time with more weight. Again, the recompression was unsuccessful and the fish floated back to the surface.

“They have swim bladders in their bodies, and those swim bladders expand in size (at surface pressure),” said Dr. Heppell. “What we really want to do is send them down, and as it gets deeper there is more pressure to compress that swim bladder enough so that they can stay down on the bottom and don’t pop up to the surface.”

Eventually, the team decided to pierce the exhausted fish’s swim bladder, and the fish was given a personal escort to the reef one hundred feet below in a diver’s arms.

It appears Cayman 27’s cameras may have been a bit of a bad luck charm that day on the water. The trip ended without a single yellowfin being caught and tagged.

Dr. Heppelll told Cayman 27 even though the day’s fishing was a wash, the Grouper Moon project as a whole has helped manage these important predator species.

About the author

Joe Avary

Joe Avary

Joe Avary has been with Cayman 27 since 2014. He brings 20 years in television experience to the job, working hard every day to bring the people of Cayman stories that inform the public and make a difference in the community. Joe hopes his love for the Cayman Islands shines through in his informative and entertaining weather reports. If you have a story idea for Joe or just want to say hello, call him at 324-2141 or send an email to

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