Moving Closer to Plenty Of Fish In The Sea: Gradual Recovery Of A Critically Endangered Fish Species

Paper: Waterhouse, L., Heppell, S. A., Pattengill-Semmens, C. V., McCoy, C., Bush, P., Johnson, B. C., & Semmens, B. X. (2020). Recovery of critically endangered Nassau grouper (Epinephelus striatus) in the Cayman Islands following targeted conservation actions. Proceedings of the National Academy of Sciences.


The Nassau grouper (Epinephalus striatus) is a large fish found in the Caribbean Sea, parts of the Gulf of Mexico, and the far western parts of the Atlantic Ocean. It is iconic and emblematic throughout its range, with many countries in the region featuring it on postage stamps. Largely solitary, it gathers in large groups called fish spawning aggregations for spawning (mating) purposes. Because of the numerous groupers that are present during these times, these areas are very popular with commercial and sport fishermen. The ease of catching grouper and their demand as food has led to overfishing and a drastic population decrease over the past decades.

Nassau grouper with diver. Source: Wikimedia.

However, a recent article by Lynn Waterhouse and colleagues published in the Proceedings of the National Academy of Sciences describes the observation methodology of the Grouper Moon project in the Cayman Islands and that country’s success thus far in boosting Nassau grouper numbers.

Project Background and Methodology:

The Cayman Islands are an autonomous British territory in the Caribbean Sea (see map below) with a long history of grouper fishing. After many years of declining grouper catches, the previously-known fish spawning aggregation was thought to be nonexistent (black dot on the map). The discovery of a new fish spawning aggregation in the early 2000s prompted the Cayman Islands government to enact strict fishing limits and other conservation measures and enter into the Grouper Moon project in partnership with the Reef Environmental Education Foundation (REEF) and scientists from the Scripps Institute of Oceanography and Oregon State University. The objective of this project is to observe and gauge the progress of conversation efforts on the Nassau grouper population in the two currently known fish spawning aggregations (the triangles in the map).

Figure 1 from Waterhouse et al, 2020.

While many countries within the Nassau grouper’s range have instituted fishing bans on this species during at least some parts of year, the Cayman Islands are alone in closing the fish spawning aggregations to fishing and other disturbances. Additionally, the Grouper Moon project is the only such project to actively and systematically monitor fish populations in the fish spawning aggregations.

Much the same way as land animals are counted, counting fish requires going to where the fish are: underwater. The necessary logistics for this aquatic work (diving gear, specialized equipment, boats, trained personnel, etc.) present an additional hurdle that must be overcome for successful marine population censuses.

Once in the water, project personnel attach a non-harmful tag to the fish and record the place and time of the tagging. Future sightings of that tagged fish are also similarly recorded. Video surveys, in which large groups of fish were recorded at one time, are also used. The video is examined later, away from the water and frame by frame, to ensure that any tagged fish are accurately counted. Examples of the videos are available at the bottom of this page, and also directly here and here.

This counting procedure is repeated annually to yield a year-by-year fish population census in the two currently known fish spawning aggregation areas.

Project Results Thus Far:

Fish population numbers from 2005 to 2018 are presented below for the Little Cayman fish spawning aggregation (Figure 2), and the Cayman Brac fish spawning aggregation (Figure 3). The A graph in each figure shows the numbers counted by the live underwater survey, while the B graph shows the numbers counted by the more frequent and reliable video surveys. Between 2008 and 2017 the number of fish from underwater surveys generally increased, though the trend is not consistent throughout the years. The more reliable and more frequent video surveys show that there is a steady increase in the number of fish from 2008 and 2018 in both areas.

Figure 2 from Waterhouse et al, 2020.


Figure 3 from Waterhouse et al, 2020.

Overall, a clear increase (almost tripling) in the Nassau grouper population has been seen from the earliest video surveys to the most recent surveys in both locations.


First, the Grouper Moon project shows that the Cayman Islands’ multifaceted conservation efforts have so far been successful in increasing the population of the Nassau grouper, which was sorely needed.

Up to now, there has not been much scientific evidence demonstrating the viability of fish spawning aggregation protection strategies as a viable tool for population increase. The population increase as described in this paper and through the Grouper Moon project demonstrates that the fish spawning aggregation protection is a successful tool in general. Therefore, such a strategy could also be enacted in other fish spawning aggregations around the world and potentially help boost the numbers of other species of fish that form fish spawning aggregations.

Third, the existence and success of the Grouper Moon project in achieving its goals of Nassau grouper population surveillance shows that government-academic-private conservation can thrive as long as all parties remain focused, invested, and united.

Finally, given that much of overfishing of Nassau grouper stems from its demand as food, personal choices also have a role to play in its conservation. Next time you see grouper on the menu, at least check to see whether the restaurant can confirm that it was legally caught. Even better, forgo the grouper altogether and choose another, non-endangered, fish.



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Munim Deen

Munim is an epidemiologist and cartographer. His primary interests are infectious disease outbreaks and their intersection with the environment, public policy, and society at large. A geographic information system (GIS) devotee, he incorporates mapping and spatial analysis into his work whenever possible. A former newspaper columnist, he holds a bachelor's degree in microbiology and a master's degree in epidemiology.

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