This year's Grouper Moon Project field season contained some unexpected surprises and raised a few questions, including "where are the fish?" Nassau Grouper normally spawn around the first winter full moon, when water temperatures drop. This is typically in late January or early February, but when the full moon falls in the middle of the months, this creates a “split moon” effect, where spawning often occurs in both months. This year was a "split moon" year, so our team of Grouper Moon Project researchers gathered in the Cayman Islands in both January and February to study the local Nassau Grouper spawning aggregations. After 24 years, we thought we knew what to expect, but the fish had other ideas! For the first time since we began monitoring the spawning site in 2001, the fish were not aggregating at their usual location on the west end of Little Cayman. Most of the estimated 9,000 resident Nassau Grouper evaded us over the ten-day field season in February, despite our best efforts to locate them.
We know that the grouper were somewhere out there, because they were not on their home reefs. This was a great reminder that nature can be unpredictable, and despite how much we think we know, science always contains some surprises! Although there was a lack of grouper at the spawning site this year, we accomplished plenty of data collection and research! Read on to learn about some of our work, including using artificial intelligence to recognize fish faces, eDNA, documenting spawning of other species, and acoustic tracking. We also continued our innovative education program, which involves over a dozen Cayman Islands classrooms and schools tuning in to several live-from-the-field chats, including two that are live-streamed from underwater! Check out the recordings of those sessions on our YouTube channel.
Fish Faces: Did you know that it's possible to identify Nassau Grouper through facial recognition - the same technology that we use to unlock our smartphones? They have unique body markings, like human fingerprints, that help distinguish individuals. By documenting these patterns, we can track their populations and monitor individuals over time. For the fish that were at the aggregation site (about 3,000 in January and about 500 in February), we used GoPro cameras to capture as many individuals as possible. These images were then put through our AI platform called Grouper Spotter. We'll be sharing more about this innovative tool later this year.
eDNA: As we first reported last year, REEF has been collaborating with scientists from Scripps Oceanography to pair our Volunteer Fish Survey Project method with passive collection of eDNA (or environmental DNA - little bits of scales and mucus and other biological matter that is floating around in the ocean, sloughed off fish and other animals and plants). Our Grouper Moon field team tested out the latest prototype of the filter, nicknamed the "SQUID". This particular application will help calibrate eDNA numbers with known numbers of Nassau Grouper in the water. Click here to read more about early work on this project.
A Special Place: Like many spawning aggregation sites, the west end of Little Cayman isn't just important for Nassau Grouper, it's where over 20 other species of fish gather to aggregate and reproduce. Even though our team didn't document any Nassau Grouper spawning this year, we were lucky enough to see spawning of Tiger Grouper and Dog Snapper. In an effort to better understand the ecology of Tiger Grouper, we collected fertilized eggs from their spawning bursts over several evenings.
Always Listening: To better monitor the movements and whereabouts of Nassau Grouper around Little Cayman, we re-installed a hydrophone array around the island. This "net" of listening stations will keep track of Nassau Grouper that we have acoustically tagged with small internal pinger tags as they move around the island.
We are grateful to our collaborators at the Cayman Islands Department of Environment for handling all of the on-water logistics and for their research assistance, and to the businesses and residents of Little Cayman, especially Peter Hillenbrand, Southern Cross Club, Little Cayman Beach Resort, and Reef Divers. The Grouper Moon Project is a conservation science partnership between REEF and Cayman Islands Department of Environment, with The Semmens Lab at Scripps Institution of Oceanography and the Heppell Lab at Oregon State University. Together with our partners, REEF has been working for more than two decades to protect and study Nassau Grouper. Learn more about this success story at www.REEF.org/groupermoonproject.