Shedd Aquarium Researchers Document the Collapse of Historic Fish Aggregation

Study Suggests Need for More Protections

Shedd Aquarium researchers published a study in the Bulletin of Marine Science today in partnership with the University of Exeter, Perry Institute for Marine Science and the Bahamas National Trust documenting the collapse of a Nassau grouper, Epinephelus striatus, spawning aggregation in The Bahamas. An important fishery in The Bahamas, the study can be used as an indicator that, despite existing protections, Nassau grouper populations are declining, suggesting a need for adapted management.

Fish spawning aggregations are fleeting gatherings of a large number of individuals for reproductive purposes. Though beneficial for reproduction, the behavior exposes species to overfishing because the aggregations are predictable in both time and space. In fact, the Nassau grouper represents one of the best known examples of a fishery collapse due to overfishing spawning aggregations throughout its range in the Caribbean and Bahamas.

In part because of overfishing, Nassau grouper are listed as Endangered by the International Union for Conservation of Nature (IUCN) and as threatened under the U.S. Endangered Species Act. The Bahamas still supports a commercial fishery for Nassau grouper, but managers have noted population declines and need for proactive, science-based management.

There are an approximated 40 Nassau grouper spawning aggregations throughout The Bahamas, however very few have been validated or studied scientifically. Shedd focused on describing Nassau grouper migrations along Andros Island, The Bahamas, which is bordered by one of the longest barrier reefs in the world. The team documented migration patterns using acoustic telemetry, a technology that uses sound pulses to track fish movements.

“After spending the last two years tagging Nassau grouper in The Bahamas during their full moon aggregations, we documented the likely extirpation of an important spawning aggregation at High Cay, a small island off the east coast of Andros in The Bahamas, which had most likely existed for decades,” said Dr. Chuck Knapp, vice president of conservation research at Shedd Aquarium. “The collapse may be the result of fishing pressure and the overexploitation of the species due to their natural reproductive behaviors.”

Using diver surveys and acoustic telemetry, Shedd’s research documented that the High Cay aggregation did not form during the 2014 – 2015 spawning season.

“The Nassau grouper fishery represents a substantial monetary contribution to the Bahamian fisheries economy, supports thousands of livelihoods, and is an iconic symbol for the country,” said Krista Sherman, research associate from Shedd Aquarium and a Ph.D. candidate at the University of Exeter. “Despite a recent national fishery closure during the spawning season, our research suggests that aggregations continue to be overfished. Our work will inform a science-based and adaptive approach for future management of the fishery.”

Given the importance of the Nassau grouper fishery, The Bahamas has implemented fishing closures during the spawning season throughout the years. In 1998, these closures included only the High Cay aggregation around full moons in December and January. In 2004, protections were increased on a national scale for up to three months during the spawning season, but varied by year. And most recently, in October of 2015, this three-month closure was fixated to Dec. 1 to through Feb. 28.

“Their precipitous declines, even with protections, underscore the need to better understand the extent, variance and current state of spawning migrations within the country,” said Knapp. “With knowledge from this study, we hope to influence management practices to ensure important spawning aggregations continue into the future.”

For more information about Shedd Aquarium’s research on Nassau grouper, visit Shedd Aquarium’s website.

VISUALS: High resolution video can be downloaded here:

Video credit: ©Shedd Aquarium/Sam Cejtin

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