Researchers keep tabs on grouper sites

Thousands of grouper aggregate at specific spawning sites after the January or February full moon. – PHOTO: PAUL HUMANN

The numbers of Nassau grouper seen at protected spawning sites around the Cayman Islands are slowly increasing, according to researchers working on an ongoing monitoring project.

Department of Environment officers and staff from the Reef Environmental Education Foundation are once again keeping tabs on aggregation sites on all three islands this week as part of the Grouper Moon project.

During the winter full moon, in either January or February, the normally solitary and territorial Nassau grouper travel long distances to gather in one spot to spawn.

It is the only time the fish procreate, and the gathering is crucial to the survival of the species, considered an iconic fish in the Caribbean.

Researchers have been monitoring the aggregation sites, which are protected from fishing during spawning season, since 2002.

Bradley Johnson, research officer with the DoE, said bad weather had held back research, which began after last week’s full moon, but he is hopeful that the necessary work can be completed this week.

“We haven’t been able to get in the water as often as we wanted to because of the conditions,” he acknowledged.

Preliminary results from the surveys that have taken place suggest the numbers remain stable. Mr. Johnson said there had been a slow increase over the years. He said it took a long time for Nassau grouper to reach sexual maturity, meaning it would take many years for the species to recover from over fishing.

The research includes volunteers counting fish and using laser calipers to measure them. Some grouper have been fitted with acoustic tags and research is ongoing, using satellite technology to track the distribution of juvenile fish.

Mr. Johnson said the study had established that grouper were resident to each island’s reef system. The DoE believes there are currently only three main spawning sites for grouper – one on each island.

“Every reproductive size Nassau grouper heads to those sites after the January full moon. They have been known to travel long distances to get there. It is in their genetic code.”
Little Cayman has by far the healthiest population, with up to 4,000 fish sometimes seen at the spawning site. There are far less on Grand Cayman and Cayman Brac, says Mr. Johnson.

The Grouper Moon project features an ever-expanding educational component involving interactive lessons, including live broadcasts from beneath the waves. More than 200 students from more than 20 schools in the Cayman Islands, U.S. and Turks and Caicos took part over the past week.

Broadcasts from the spawning site had to be canceled because of the weather, though live sessions were still held from the Bloody Bay Wall in Little Cayman using special underwater cameras and microphones.

The Grouper Education Project also features classroom sessions emphasizing the value of the fish as a “keystone predator” on the reef and highlighting the conservation challenges facing the species.

“While the bulk of the lessons take place over the course of the two weeks in January and February, when REEF scientists and DOE staff are working at the spawning site, we have developed a set of pre-activities to help build background knowledge as well as follow-up lessons to help deepen the students’ learning experience,” REEF and the DoE said in a press release promoting the education project.

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  1. Thanks to DoE and the EEF for the good job they are doing, to monitor and protect the groupers spawning habitat.
    Just the other day I was listening to a family member tell how when she was a child, over seventy years ago, that there were so many groupers and conchs and lobsters, that they could not even sell them. So they would salt and dry for rainy days and sometimes had to throw them away because of not having refrigerators.
    Today just imagine how that has changed; we are protecting them. But it is something we need to do, or in a few years we will not have any left.
    Still saying that a closer monitor need to be done on night divers.