Mar 18, 2011


by Guy Harvey


Returning from an inspiring documentary shoot in Little Cayman last week, I have been itching to tell the story of how cooperation between the private sector, non-governmental organizations (NGO) and government entities is working to assist in the conservation of fish species in the Cayman Islands. Following the public outrage of the massive extraction of Nassau groupers at their spawning sites in the Sister Islands nine years ago, the Marine Conservation Board (MCB) acted on a recommendation from the Department of Environment (DoE) to close the Spawning Aggregation (SPAG) sites to any form of fishing for eight years. For a small nation that heavily depends on diving tourism for income, that was a smart move. Hooray for common sense!

My opening line in the documentary goes “Throughout the warm waters of the western Atlantic and the Caribbean, one species of fish that stands out as the icon of the coral reef environment…the Nassau grouper.” So why are we still catching Nassau grouper if their numbers are so low?

Spawning sites for Nassau Grouper in the Cayman Islands need protection

Protection for the spawning adults was quickly put in place. Meanwhile, Nassau groupers over 12 inches in length, could be caught for the rest of the year anywhere in their range in the Cayman Islands. Eight years have flown by. The ban on fishing the SPAGs is now up for review by the MCB just as the results of all this effort are just starting to pay off for the Nassau groupers. It is quite apparent that this conservation effort (via closed areas and closed seasons) needs to continue for generations to come. As an icon in the Caribbean, the Nassau grouper is featured in photographs, calendars, logos, signage, and in television shows from Belize to Trinidad.  Nassau groupers can be conditioned toward divers and can make a divers experience go from a good dive to a great dive when one is encountered. 

What impressed me most about this research effort was that every aspect of the life history of the Nassau grouper has been studied. Brice and Christy Semmens are leading the charge. Christy is the Scientific Director at REEF (please visit They were assisted by Dr. Steve Gittings who is National Science Coordinator of the National Marine Sanctuaries at NOAA as well as several other PhD students and volunteers. In addition, the Cayman Island Dept. of Environment has conducted age and growth studies as well as tracking, using sonic transducers and listening receivers deployed around all three islands. Lead in the field by Phil Bush, with James, Keith, Delwyn and Kevin, the DoE played a most important role in delivering logistical support and personnel, critical in the execution of the research.  Use of the RV “Sea Keeper” was critical as a large platform from which to dive in rough seas and strong currents.

Because one SPAG site on the western end of Little Cayman was deemed as still viable, most of the research effort has been concentrated there. Heavier fishing pressure around Cayman Brac and Grand Cayman, have taken its toll, resulting in only a few hundred adults still turning up for the annual spawn.

So how did we arrive at this situation? The biology of the Nassau grouper works against its chances of accommodating any prolonged level of exploitation because it is a long lived, slow growing fish. This species aggregates in large numbers annually in the same place at the same time of year. Once humans find out about these “grouper holes”, greed takes over and they are fished until annihilated. Many species of grouper have the same spawning behavior. As a good example of how effective conservation can be, only twenty years of protection for the biggest of all groupers, the goliath grouper, has resulted in a revival of this species in Florida. The black grouper, yellowfin, red grouper and Nassau grouper, all need the same protection if they are to recover.

Historically the Cayman islanders fished the groupers in the grouper holes taking just what they needed. Apparently, twenty fish per day, per boat was the typical catch. As there was no refrigeration, the fish were salted and dried for later consumption. During grouper season, so many groupers were drying at homes on East End, you could smell them from Pease Bay and Bodden Town if the wind was right. At some point in the 1950s and 60s, the word got out and mother boats came from Jamaica to buy Nassau groupers from the local fishermen. They put the catch on ice and took the fish back to Jamaica to sell. Tens of thousands of Nassau groupers were caught each season resulting in a steady decline. With no quotas or limits, the population became a shadow of its pre-exploitation levels. Since then, relentless fishing by, local artisanal fishermen, of the remaining adults at the SPAGs, further reduced each SPAG to the hundreds. The same story has taken place throughout the range of the Nassau grouper. Now, before it is too late, renewed efforts in grouper conservation in the Bahamas and in the eastern Caribbean are being initiated based on the example set by Cayman.

Once, it was widely believed that recruitment of juvenile reef species to an oceanic island population was brought about by larval drift from other islands and land masses up current. The misconception prevailed that the Nassau grouper “can’t done, and more will come from the ocean”. Eight years of current and tide studies now show that the fertilized eggs from the SPAGs on Little Cayman leave the island for a short period, but then are brought back by the current eddy or gyre. The parent groupers wait until the current is slack to spawn and the fertilized eggs are broadcast at dusk, reducing predation. The eggs hatch into larvae while suspended in the plankton and grow into juveniles before settlement on the reef.  Drift studies conducted by REEF and by Dr. Scott Heppell of Oregon State University show that the larvae do not travel far from Little Cayman—some may also end up on Cayman Brac. During daylight hours, mortality of eggs, larvae and juveniles is very high due to other planktonic predators.

The data shows that a marine protected area is appropriate in the Cayman Islands

In addition, the scientific team proved that the brood stock participating in the SPAGs only came from Little Cayman and not from Cayman Brac, Grand Cayman, Pickle Bank, Jamaica or Cuba, as some fisherman believed. In fact, there is very little connectivity of island populations throughout the Caribbean, which strengthens the case for conservation of each island’s brood stock or “capital”.

Sonic tracking and visual observations by divers prove that all the mature Nassau groupers travel from their home reef patch on Little Cayman to the SPAG around the time of the full moon in January, February and March. Here, divers still see the grouper migration by day heading to the west as they respond to the reproductive stimuli that have operated successfully for millions of years, enabling sustainable existence for all that time… until man came into the picture.

Another detrimental influence caused by man is the invasion of a Pacific species, the Lionfish. We were joined in Little Cayman by Chris Flook of the Bermuda Aquarium. Lionfish are a small but highly aggressive predator on Cayman reef and have severely impacted smaller reef fish and invertebrates. Chris said, that in Bermuda, they have taken over many cleaning stations, first eating the species that clean other reef fish, including groupers, and then, lie in wait for other fish coming to be cleaned. The same must be happening here. They will also consume juvenile groupers. Research work on lionfish is also being conducted at the Central Caribbean Marine Institute (CCMI) where local dive operators are helping in the collection and eradication of this very dangerous and invasive species. Juvenile Nassau groupers being recruited from the plankton to the reef environment have to avoid another unfamiliar predator, the lionfish.

During the day, the DoE and REEF teams ran a number of counts to estimate the adults participating in the SPAG. About seventy groupers were tagged with spaghetti tags as well as divers using visual and video counts to obtain these estimates. Other divers used lasers attached to underwater video cameras to measure individual fish without having to catch them.

Many groupers stayed close to the bottom or on the bottom and in coral crevices during the day. In the afternoon, they formed a larger cohesive school, and the closer they got to the spawning night, the more the grouper changed colour. Some turned dark losing their characteristic banded pattern, while others assumed a bi-colour phase dark chocolate brown above and brilliant white below with a white stripe through the eye.

— Guy Harvey

See our next week’s blog for Part II

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