This publication from the Grouper Moon Project addresses the question of where fertilized eggs go after being released by Nassau Grouper at their spawning site off the west end of Little Cayman. On nights of spawning in 2017, researchers physically tracked clouds of tiny, transparent Nassau Grouper eggs through the night with an underwater microscope developed by scientists at Scripps Oceanography. Results show that fertilized eggs from Little Cayman floated back onto reefs on the island. Drawing on these direct observations and ocean current data collected on spawning nights at Little Cayman, the authors also used a computer model to investigate where the fertilized eggs likely went in 2011 and 2016. The model predicted that many of the baby Nassau Grouper ended up back at Little Cayman in 2011, a suggestion that dovetails with prior research (see here) showing that the 2011 reproductive season led to a significant population increase around Little Cayman. For 2016, the model predicted that currents carried some fertilized eggs to the nearby island of Grand Cayman.
This study highlights how reproductive success and the final destination of the grouper eggs can vary from year to year, while also showing that local conservation measures to protect Nassau Grouper are boosting local populations and sometimes providing spillover benefits to neighboring islands. It is also an example of the power of collaboration - scientists from several departments at Scripps Institution of Oceanography led the work, who were assisted by REEF's Grouper Moon field team and supported in the field by the Cayman Islands Department of Environment vessels and crew. To learn more about the Grouper Moon Project, visit www.REEF.org/groupermoonproject. To read more about this study, visit this Scripps article about the work.