Of rays and groupers, the icons of Cayman’s reefs

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Recently I assisted team members of the Guy Harvey Research Institute conducting the first census on the stingray population at the Sandbar since July 2008. We were ably assisted by the Department of Environment and the research was led by Dr. Mahmood Shivji, director of the GHRI based at Nova Southeastern University in Florida and Dr. Brad Wetherbee of the University of Rhode Island. Both scientists have over 25 years of experience working on sharks and rays and directed the last ten years of work on the Cayman stingray population.

When I first came to Cayman in 1999 I was impressed with the number of animals at the sandbar, but amazed that no research work had been done on this population of wild animals. For two years in 2002/3 the GHRI assisted by the DoE did a comprehensive population analysis of the rays, the first ever conducted on rays in a marine wildlife interactive programme.

This baseline data was invaluable for the management of the resource and for any future research work on the individual rays. Basic information such as width, weight, sex, DNA samples, migrations and diurnal behaviour were collected.

I produced an informative documentary about the rays and their biology which I distributed at no charge to all schools, government departments, dive and stingray tour operators.

PIT tags, similar to microchips used in pets, were placed in each ray to allow identification of individuals and therefore tracking of their growth over a long period. Over successive counts tag retention was found to be 100 per cent. All rays over a certain size had tags, only new young recruits to the sand bar did not have tags.

A sample of one hundred rays was taken every month for six months in each year to determine population composition, growth and pregnancy rates. It was likely that every ray that visited the sandbar in that time was sampled and tagged. Site fidelity was strong with only one animal visiting the stingray city from the sandbar and then returning. These animals are long lived slow growing relatives of sharks so it was expected that many rays would visit the sandbar for 20 years or more.

Christine Semeniuk, from Canada did more work on stingrays in 2005, mostly to investigate their wellbeing using blood analysis. The next census was done by GHRI/DoE in early July 2008. On the first day of the census, July 1, we sampled 51 rays, the next day 40, and only 8 on the last day as most rays had already been caught measured and put back in the water.

In the last year I have noticed, as well as several tour operators, a decline in number of the rays experienced at the sandbar. No complaints came from the tens of thousands of visitors, but many of us living here were disturbed by this apparent trend.

Another census was required. In mid January 2012 the same team working on the same amount of time and effort caught and measured 61 animals. Sounds like there are plenty of rays to go around but that is a 38 per cent reduction in the sandbar stingray population compared to 2008. 43 rays were recaptured and 18 new recruits were tagged. Of particular note is that only 43 of the 99 animals counted and tagged in the 2008 census were sampled in 2012.

For complete scientific analysis another census will be conducted in July 2012 to compare numbers for the same time of year as the 2008 census. However the question is loud and clear and needs to be addressed; what has happened to the stingrays?

What are we doing about it? Each stingray is clearly worth in the order of a hundred thousand dollars per year to the Cayman economy. Over a ray’s long lifetime it is worth several million dollars to the Cayman economy. So how is it that the rays enjoy protection only in the wildlife interaction zone areas? Why are these extremely important animals not totally protected from harvest all around the Cayman Islands?

Our data suggests that the rays have not migrated to other sites as site fidelity is very strong. We saw no evidence of shark attacks and all animals appeared healthy… so fishing mortality remains the main suspect for the sudden decline. The Marine Conservation Law needs to be changed to protect stingrays throughout the Cayman Islands.

The Marine Conservation Board is to be congratulated for extending the ban on fishing the spawning aggregation sites of the Nassau grouper. This ban extension has been based on the ten years of detailed scientific research on the Nassau grouper by the Department of the Environment and the Reef Environmental Education Foundation (REEF), mostly conducted in Little Cayman.

Little Cayman has the last remaining viable SPAG site in the greater Caribbean. There used to be tens of thousands of Nassau groupers here in the Cayman Islands. Up to 2002 they have been systematically targeted for decades during their spawning aggregations by local fishermen and the numbers have declined to the point where the species is now categorized as critically endangered by the International Union for the Conservation of Nature.

A basic premise of fisheries management is that a species be allowed to replace itself and that extraction does not exceed natural replacement. But this has not been the case here. Fishing for Nassau groupers continues year round outside the SPAGs which has not allowed the population to grow in spite of the limited protection.

What is now needed is for the Marine Conservation Law to be changed to provide total protection for Nassau groupers during their spawning season from 1 November to 31 March throughout their range.

From the eco-tourism perspective, the diver’s encounter with a grouper or several groupers for that matter can turn a good dive into a great dive. Over the last 20 years the value of a living grouper to the Cayman Islands economy far exceeds that of the grouper fillet on a plate served at home or in a restaurant. Limited, regulated artisanal fishing for this species may be resumed once the grouper population has recovered to around ten thousand mature individuals.

It will be good for the economy if the Cayman Islands government takes further action to conserve and protect these iconic marine species. Conservation is good for business. Tourism is one of our main sources of income. Seven Mile Beach and the stingrays at the sandbar are the top two reasons people visit Grand Cayman. The groupers in Little Cayman are the top reason why divers visit this tiny island.

The Cayman Islands were recently voted the best dive destination in the Atlantic/Caribbean by Scuba Diving Magazine. Tremendous news! Our landside infrastructure and hospitality, high quality dive operators, marine life and natural beauty all contribute to this experience.

Will we remain at the top of we continue to eat these creatures, the icons of the reef, that got us to the top?

It is our collective responsibility to conserve the marine environment and maintain the biodiversity of the planet.

Fish responsibly, dive safely.
Guy Harvey, PhD.