![]() To find out, the team combined multiple lines of data and executed a tightly choreographed marathon of field work. They wanted to know if Little Cayman grouper were replenishing their own numbers, and if this healthy population could potentially seed recovery on other islands. Stock said this is one of the key reasons he and his colleagues wanted to track the fertilized eggs from Little Cayman, which hosts the largest known aggregation of Nassau grouper in the world. ![]() This means that populations will only rebound through local reproduction or through lucky years when the currents ferry in larvae from larger populations on other islands. One of the key research findings from the Grouper Moon Project, a conservation science partnership between REEF, the Cayman Islands Department of the Environment, and researchers from Scripps and OSU started in 2002, is that Nassau grouper don't island hop as adults. Grand Cayman's population has yet to show signs of recovery, but conservation measures provide an essential foundation for a big reproductive year to restart the population. In that same time period, the population around nearby Cayman Brac grew from about 500 to 2,000. On Little Cayman, protection allowed the Nassau grouper population to recover from around 2,000 fish to roughly 7,000 by 2018. The Cayman Islands government enacted temporary protections that halted fishing in 2003, and established permanent protections in 2016 that included no fishing during the spawning season (December to April) as well as year round size and number limits. By the 1980s most populations had steeply declined and many spawning aggregations no longer formed. There were once millions of Nassau grouper in the Caribbean, but their spectacular full moon aggregations made them easy targets for fishers. "Getting this done was a huge technical challenge that really benefited from bringing together the wide ranging expertise of Scripps scientists." at Scripps and who is now a scientist with Norway's Institute of Marine Research. "This study helps us understand one of the key physical processes behind any population growth or conservation success we end up seeing for this important, endangered reef fish," said Brian Stock, the study's first author who conducted the research as part of his Ph.D. The study demonstrates 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. For 2016, the model predicted that currents carried some fertilized eggs to the nearby island of Grand Cayman-a population of Nassau grouper that has not recovered as well as the one on Little Cayman. 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 showing that the 2011 reproductive season led to a significant population increase around Little Cayman. Drawing on these direct observations and ocean current data collected on spawning nights at Little Cayman, the team also used a computer model to investigate where the fertilized eggs likely went in 20. In a new study, published May 10 in the Proceedings of the Royal Society B: Biological Sciences, the researchers show that fertilized eggs from the Little Cayman spawning site floated back onto reefs elsewhere on the island in 2017. Scientists at the University of California San Diego's Scripps Institution of Oceanography, Oregon State University (OSU), and the conservation organization Reef Environmental Education Foundation (REEF) teamed up with the Cayman Islands Department of the Environment to address this question by physically tracking clouds of tiny, transparent Nassau grouper eggs through the night with an underwater microscope developed by Scripps Oceanography Marine Physical Laboratory scientist Jules Jaffe. But where do these eggs end up after they're cast adrift? These precious fertilized eggs are the engine that powers the still-limited recovery of this critically endangered species that is a key reef predator and was once the target of an important fishery in the Caribbean.
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