Around the full moons of January and February, the islands’ Nassau grouper populations converge for a mass reproduction event.
Scientists from the Department of Environment and reef.org have been monitoring spawning aggregations across Cayman since 2002 as part of the Grouper Moon project, and they told Cayman 27 the preliminary numbers for this year’s event are encouraging.
“It’s a magical experience, something that just blows my mind,” said Dr. Brice Semmens of the Scripps Institute of Oceanography at the University of California at San Diego.
He described the scene as thousands of Nassau grouper congregated off Little Cayman’s west end for their annual mating ritual, the grouper moon. This spawning aggregation is regarded as the largest in the Caribbean, and one of three known to exist in Cayman waters.
“There is good evidence to suggest that the population on Little Cayman is growing very rapidly, and just this year really good evidence to suggest that the population of over in Cayman Brac is also growing. The story is not so clear for Grand, in part because there’s just so few fish left here on Grand,” said Dr. Semmens.
Grand Cayman’s spag population has steadily declined through the years. This year’s figures indicate a population of just three to four hundred Nassau grouper participating in the spawning event.
DOE Senior Research Officer Croy McCoy said the Cayman Brac spag has shown a rebound.
“Cayman Brac was a bit of a struggle for a long time there, looking at very low numbers, a few hundred maybe like 500,” said Mr. McCoy.
After 15 years of research, many mysteries remain about the grouper moon. Dr. Semmens told Cayman 27 scientists are following the eggs to find clues.
“We’re starting to do some really cool stuff with tracking eggs and underwater microscopes to start to unveil some of that science that we don’t currently understand,” he said.
The scientists are using “drifters” to track the eggs, and they are finding the grouper spawning takes place on nights where the currents create eddies to keep the eggs near to the island.
They said populations with more fish release more eggs, which help expedite a population recovery.