Thousands of Nassau groupers have commenced their annual spawning dance, also known as the Grouper Moon, in the pristine waters of Little Cayman.
Sunday night researchers surveying the annual event observed the first spawning at the aggregation site.
Volunteer Amanda Brown has been documenting the grouper spawning through a blog and described the sight as “incredible”.
“Bands of a dozen or so groupers shot upward in front of us, like fireworks. Each band consisted of many males pursuing a single female. The female grouper would shoot up into the water column swimming straight up to release her eggs, and several male groupers would follow, swimming in spirals around her,” she wrote.
The unique spectacle usually attracts international researchers and volunteers from the Reef Environment Education Foundation who come together for the Grouper Moon project which has been a mainstay since 2002.
However, due to COVID-19 restrictions, the REEF team was unable to attend to participate in the monitoring and study of the Nassau grouper spawning aggregations.
But a team of Department of Environment scientists and volunteers are tracking the fishes, which are listed as threatened.
According to posts on the DoE Facebook page, the spawning event has commenced, and data is already being collected.
Researchers are measuring the size of the fish engaged in spawning.
The video below shows the Nassau grouper during spawning.
“Our team uses a specially designed device in the ‘Stereo Video’ research method to measure the length of different Nassau grouper at the spawning aggregation site. The stereo video device is a long rod with a GoPro on each end. Computer analysis of the images measures the length of each fish photographed,” the DoE said.
Knowing the length is important, the department said, because the larger the fish are, the more eggs they will have.
“Also, since the fish get bigger as they get older, this is one way to determine the population growth and maturity. Our researchers love to see not only more fish, but more fish of varying, and increasing sizes,” it added.
Apart from the “stereo video” research method the team in Little Cayman is also using the “Fish Faces” research method to map fish during spawning.
“Each grouper has a unique pattern so researchers are obtaining images of individual grouper ‘faces’ or the sides of the grouper. Researchers can then use AI software to identify each fish to obtain an estimate of the population size,” the DoE said in one Facebook post.
The Nassau grouper population on Little Cayman has rebounded over the last 15 years.
Preliminary estimates from last year’s survey showed that 8,000 Nassau groupers were recorded in Little Cayman and 3,000 in Cayman Brac.
Brown, in her blog, shared that on Sunday night several Caribbean reef sharks were seen swimming through the Nassau grouper aggregation site, “which was an exciting way to watch the food web in action with the incredible apex predators amongst the groupers”.
She also pointed out that the team found a large plastic bag floating in the ocean at the aggregation site which was removed by Paul Chin from the Grouper Moon team.
“Plastic pollution is an ever-growing problem around the world. Seeing large plastic bags like this in the ocean is devastating as sea turtles, fish, or other marine life could easily become entangled or ingest the plastic. It is estimated that eight million tons of plastic enters our ocean every year, which is in addition to the estimated 5.25 trillion pieces of plastic already in the ocean,” she wrote.
Brown said everyone can help to stop plastic pollution.
“You can help to reduce plastic pollution in our oceans by refusing items that come in single-use plastic packaging, recycling, participating in beach cleanups, and educating others about plastic pollution. Together, we can make a difference,” she said.
From 1 Dec. to 30 April, fishing for Nassau grouper in the Cayman Islands is prohibited.
The season for the fish opens in May, and the limit is five per person or five per boat per day, whichever is less. Only Nassau grouper between 16 and 24 inches long can be taken, and only with a hook and line.