Numbers falling at famous Stingray City
(CNS): Research conducted by the Guy Harvey Research Institute with the Cayman Islands Department of Environment has confirmed fears that the number of Stingrays at the Cayman Islands most popular tourist attraction are falling. The census this year found the stingray population at Stingray City has decreased by around 38% compared to the last census in 2008. The researchers have also raised concerns over the low number of male samples tagged in the most recent analysis and are now trying to find out why the numbers are falling. Blood samples have been taken by researchers to determine if the diet of squid fed to the rays by the majority of tour operators is affecting the animal¹s health.
“A long-term plan of monitoring the numbers of rays and their health is required,’ said officials from the Guy Harvey Research Institute (GHRI) in a release this week. “Everyone in the Cayman Islands benefits from the presence of this unique marine interactive site. Every advertising campaign or tourism related article featuring the Cayman Islands has these iconic animals up front and prominently displayed. It is time the government of the Cayman Islands returned the favor by supporting on-going research of the stingrays¹ population status and well-being by releasing funds in the Environmental Protection Fund collected for this purpose.”
The Sandbar in the North Sound has a large number of wild rays that are accessible to tourists every day of the year. As a result the socio-economic value of the rays to the Cayman economy is enormous. On average, each animal can generate up to $500,000 in revenue per year, or $10,000,000 over the course of a 20-year life span.
Research was started by the GHRI in 2002 when all the stingrays that frequent the two main sites were caught by hand and tagged with a PIT (passive integrated transponder) at the base of their tail. During the initial count, 164 rays were tagged, weighed and measured at the Sandbar over two years. Since then, tag retention has remained near 100% so many animals tagged ten years ago still have their PIT today. The sex ratio of 90% females to 10% males has remained fairly constant over this time.
From 2010 tour operators and casual observations indicated a sudden decline in the number of rays at the Sandbar. The GHRI conducted a census in January 2012 and sampled only 61rays in the standard three day research period representing a significant 38% decrease in numbers compared to 2008 count.
Armed with this information researchers are now eager to find out what has caused the decline. Predation by sharks has been ruled out for a lack of evidence of shark bites and the corresponding demise of sharks. However, fishing mortality is a consideration as there is no national protection for stingrays - outside of the Wildlife Interactive Zones (WIZ) .
Another possibility is the overall health of the rays, which is why GHRI enlisted the support of the Georgia Aquarium veterinary staff for this year¹s census. The addition of the GA vets also allowed the research work to become much more technical. Dr. Tonya Clauss (Director Animal Health, Georgia Aquarium), Dr. Lisa Hoopes (Nutritionist, Georgia Aquarium) and Nicole Boucha (Senior Veterinary Technician, Georgia Aquarium) arrived in Grand Cayman loaded with equipment to take blood and store these precious samples in liquid nitrogen until analysis could be achieved back in Georgia.
Over three days in July the team sampled 57 rays only 5 of which were male at the Sandbar down from 61 in January with assistance from DoE staff and several volunteers. The team also spent a day at the original Stingray City and sampled 11 rays , just 2 male) and caught 3 rays at Rum Point, bringing the total to 71 rays sampled.
Each ray was caught by hand and transferred to the pool in the workboat where they were measured and tagged, and then blood was taken from the underside of the base of the tail. Some of this blood was immediately centrifuged to make counts of white blood cells. The rest was frozen in liquid nitrogen for shipment back to the lab in the Georgia Aquarium.
The processing of samples and data will take several weeks the researchers hope to have a better idea about what is undermining these valuable creatures and how better to manage their future well-being.
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