Nassau Grouper spawning project designed to strengthen sustainable management

Nassau grouper spawning aggregation survey. PHOTO CREDIT: Keith Pamper
Nassau grouper spawning aggregation survey. PHOTO CREDIT: Keith Pamper

By: Krista D. Sherman (University of Exeter), Dr. Kristine Stump (Shedd Aquarium) and Dr. Craig P. Dahlgren (Perry Institute for Marine Science)

[dropcap]N[/dropcap]assau grouper is one of the most important fishery species in The Bahamas and wider Caribbean, but due to heavy over exploitation this fish is endangered and is scarce in many marine ecosystems throughout this region. Bahamians have fished grouper for centuries, and the fishery supports thousands of livelihoods, saturating the social fabric of the country. Aside from socioeconomic benefits, Nassau groupers are ecologically important species, helping to maintain balance within coral reef ecosystems.

Within The Bahamas, Nassau grouper travel up to hundreds of miles to form annual transient fish spawning aggregations of hundreds to thousands of fish to reproduce during the winter full moons between November and February. Spawning takes place around sunset, with smaller groups of fish leaving the main school and rushing up into the water column to release their eggs and sperm. Successfully fertilized larvae float to the surface and are circulated by ocean currents for over a month until they attain the appropriate size to settle into nearshore habitats like mangroves and patch reefs. As recruits, or juveniles, they continue to grow in these nearshore habitats before migrating to coral reefs as adults. Unfortunately, spawning aggregation sites are often well-known by fishers, making this iconic species particularly vulnerable to exploitation. Fishing the spawning stock at aggregations poses a serious threat to the species’ continued existence. The Bahamas is one of the few remaining countries where Nassau grouper populations still support multiple active spawning aggregations.  Since 2004, the Bahamian government has implemented seasonal bans on fishing for Nassau grouper during their spawning period. Unfortunately, despite the fishing embargo, numbers of grouper at some historic spawning sites have decreased, some spawning aggregations have disappeared, and commercial landings have been declining for more than two decades.

There are significant knowledge gaps with regards to the status of remaining spawning stocks throughout The Bahamas. To address these deficiencies, Dr. Kristine Stump, Postdoctoral Research Associate with the Shedd Aquarium’s Daniel P. Haerther Center for Conservation and Research, Krista Sherman, PhD student at the University of Exeter and Dr. Craig Dahlgren with the Perry Institute for Marine Science have embarked on a three year collaborative research project to investigate the status and dynamics of Nassau grouper spawning aggregations throughout The Bahamas. The team is using cutting edge research techniques including advanced acoustic telemetry, genetic analyses, blood physiology, bathymetric mapping and biophysical modeling.  Since 2014, the team has conducted research at several islands throughout the country. An array of acoustic bottom monitors or listening stations has been set-up along the continental shelf of Andros and at a spawning site off Long Island to describe movements of Nassau grouper to, from and within aggregations. To date 65 fish have been externally tagged, 46 surgically implanted with acoustic transmitters, and 32 blood samples and 48 fin clips collected for genetic testing. The genetics work is particularly important, as it will help explain how grouper movements and larval transport throughout the Bahamas affect population connectivity and therefore the continued success of the species. 

Results will be used to inform sustainable and adaptive management of this endangered, but heavily exploited species, with support from the Department of Marine Resources and local non-governmental agencies in The Bahamas.

For more information on about this Nassau grouper research project follow us on Facebook , Twitter @SheddResearch and Instagram @grouperresearch242.