Research Highlight: Grouper Moon Project Uses Scripps Science to Revive a Caribbean Fish

To its own detriment, the Nassau Grouper is a creature of habit.

Large and charismatic, this Caribbean fish travels great distances to mate at specific spawning sites every year. These spawning aggregations take place a few days after full moons in January and February, and that’s it. The fish remain celibate the remainder of the year. 

This aggregating behavior makes the grouper easy prey for fishermen who know of these habits and target the fish with destructive efficiency. Most Nassau Grouper populations in the Caribbean have collapsed over the past fifty years as technology and market demand have combined to ratchet up fishing pressure. But now Brice Semmens, a marine biologist at Scripps Institution of Oceanography at University of California San Diego, and a team that includes other scientists and government officials are turning this trend around in the Cayman Islands.

In 2002, the Cayman Islands Department of Environment and a citizen conservation group called Reef Environmental Education Foundation (REEF) began a collaborative study on local Nassau Grouper populations following the discovery of a uniquely large spawning aggregation of the species on Little Cayman Island. In 2005, Semmens joined the study, dubbed the Grouper Moon Project. Thirteen years later, he and his students are still members and have introduced advanced conservation technologies in which Scripps Oceanography specializes.

The Cayman government initially enacted a ban against fishing at the aggregation sites for an eight-year period shortly after the creation of the Grouper Moon Project. It extended the ban in 2011 as a direct result of the science generated by the project. In 2016, the government instituted a permanent seasonal closure for Nassau Grouper during their spawning season. During the remainder of the year, take of the species is limited to certain size and catch limits. Only certain fishing gear types are allowed.

“In 2008, there were roughly 1,500 fish on Little Cayman Island,” said Lynn Waterhouse, a graduate student in Semmens’ lab. “As of 2018, there are about 6,000 individuals. This massive increase in population size would not have been possible without the success of management regulations.”

Semmens credits the rebound to his lab’s relationship with the Cayman Islands Department of Environment as a research partner and collaborator.

“The science, while cool and theoretical and interesting, is also massively applied. Once we get the answers, they are subsequently used in Cayman Islands governance,” he said.

Semmens and the team maintain a set of acoustic recorders around the islands to determine the population size of Nassau Grouper and understand the movements of individual fishes. Nassau Grouper make distinct sounds that are recorded by hydrophones, while other instruments are set up to record pings from tracking devices tagged on some of the fish. During spawning events, scientists launch drifters with GPS devices and satellite phone. Designed to float with the current, each drifter’s track reveals information about the dispersion of grouper eggs and juvenile fish.

To confirm that the drifters follow the same path as the eggs, Semmens brought in Scripps physical oceanographer Jules Jaffe, an expert in marine robotics known for inventing underwater microscopes among other instruments. Jaffe and his team engineered a special underwater microscope that is towed behind a boat and takes high-resolution photographs to confirm the movement of grouper eggs and larvae along island currents.

Semmens and the team also collect eggs at the aggregation sites and bring them back to the lab in order to learn how many are fertilized, and of those how many hatch.

“The fertilization rates have been consistently high,” said Waterhouse. “We are continuing this project into the future to keep tabs on what effect changing ocean conditions may have on egg and larval survival.”

In a new phase of research, the team is now studying whether there is any correlation between water temperature and reproductive success. There is evidence to suggest that eggs and larval fish are sensitive to ocean warming, which could pose another threat to the revival of the Nassau Grouper.

Semmens and the Grouper Moon Project team are involved in a variety of outreach activities aimed at engaging Caribbean communities and gaining local support for environmental protections. Semmens visits local classrooms to discuss the importance of the long-term study, and takes classrooms on virtual field trips via Google Hangouts, answering questions while scuba diving. REEF projects engage citizen scientists, locals and visitors alike, including worldwide surveys where volunteers can add their sightings from snorkeling or scuba diving trips to help track fish populations. The team worked with PBS, which led to a documentary about the Grouper Moon Project.

The success story of the Nassau Grouper’s rebounding population even made it into entrepreneur Richard Branson’s blog after he visited the research team. A student on Grand Cayman turned out to be arguably an even more important ally after he wrote a timely open letter in 2011 to local politicians urging them to protect the fish. Inspired by a Semmens classroom visit, the student had the letter published in a local newspaper just before the vote to extend the fisheries protections before they expired.

“Ultimately all of this is aimed at restoring healthy fisheries,” Semmens said. “We’re not just about conserving the fish, we’re about making it so that there’s enough fish for divers to see, enough fish to fill the ecological role they’re supposed to fill, and enough fish so that people can put fish on a plate reliably.”

Semmens has since brought the lessons of the Grouper Moon Project back to Southern California. The coastal waters of San Diego and Orange counties are a patchwork of state and federal marine reserves, none drawn without controversy as fishers, divers, and the coastal tourism industry lobby for the livelihoods dependent on marine life.

In order to study the effectiveness of these protections, Semmens has set up an array of more than 40 electronic listening stations in waters off La Jolla, near the Scripps campus. Receivers are attached to the seafloor and record the pings of tracking devices that have been attached to multiple species of fish. Semmens’ team gets help from local fishing enthusiasts to catch and tag fish. There is also a website and app where anyone who catches a tagged fish can report details that add to the dataset.

Semmens recently became director of the California Cooperative Oceanic Fisheries Investigations (CalCOFI), a 70-year-old entity with its own roots in solving the mysteries of a disappearing fish population. The partnership between Scripps Oceanography, NOAA, and the California Department of Fish and Wildlife was formed to analyze the collapse of the California sardine fishery that took place in the 1940s. CalCOFI has since broadened its focus to include research on other fisheries and to consider the interplay of biology, chemistry, and physics of the California Current ecosystem in ever-greater depth.

Semmens said he hopes to increase the local community’s investment in CalCOFI, bringing a bit of the Grouper Moon spirit back home.

“We have by far the best and most comprehensive long-term ocean monitoring program in the world, right here,” he said. “People should be proud of that and we should also be using that to improve the quality, consistency, and sustainability of ocean experiences and products for Californians.”

– Melissa Miller

Related Image Gallery: Grouper Moon Project Uses Scripps Science to Revive a Caribbean Fish