In the summer of 2009 I worked with Dr. Terry Norton, Amy Hupp and Stefanie Ouellette to conduct a health assessment of two species of shark commonly found off the coast of Georgia and Florida. You may be familiar with these two species: the Atlantic Sharpnose and the Bonnethead. Anglers on the beaches of Georgia’s barrier islands commonly catch both. The Bonnethead is closely related to the Great Hammerheads. We know very little about either species: obtaining baseline health data may help us better understand the life history, habitat use, and population status of these two common sharks.
The project was a collaboration between the Georgia Sea Turtle Center, Tufts University Cummings School of Veterinary Medicine, the Georgia Aquarium, the Georgia Marine Extension Services, and the South Carolina Department of Natural Resources. I spent 3 weeks out with the crew of the Georgia Bulldog in July 2009. The Georgia Bulldog is a shrimp boat modified into a research vessel and was out trawling to catch none other than sea turtles! The TEDS (turtle excluder devices) had been removed from the nets of the GA Bulldog and the nets were trawled for 20 minutes many, many times a day. The goal: an in-the-water study of sea turtle abundance off the coast of Georgia and Florida.
So, where did the shark project fit into the catching of sea turtles? Sharks are often captured in the nets as bycatch and Sharpnose and Bonnetheads are the two most commonly caught sharks in the nets of the Georgia Bulldog. We decided to opportunistically sample from the sharks captured: a total of 17 Sharpnose and 16 Bonnethead were bled, measured, weighed, and given a complete physical exam. All sharks used in this study appeared healthy!
While we are still working to process our data, we discovered several very interesting and important things about the wild-caught sharks. We tested for antibiotic resistance in the bacteria that grow just inside the cloaca of the sharks. We found that antibiotic resistance is quite prevalent in sharks sampled, indicating that somehow antibiotics used by people and on farms are making their way into our marine ecosystems.
Another thing we discovered is that the Vitamin A and E levels in the wild sharks are much, much lower than those found in some captive sharks. Interestingly, some captive sharks develop spinal deformities while in captivity. The cause of this spinal deformity is currently unknown. This is where the Vitamin A and E levels play in: a captive shark with spinal deformity had over 100 times the levels of Vitamin A and E that we found in the wild Sharpnose and Bonnetheads! Vitamin A toxicity can cause many health issues in animals with boney vertebrae: most notably demineralization of the bone. (Vitamin A is important in the remodeling of bone.) Since sharks do not have boney vertebrae (they are cartilaginous!) we do not know what the specific mechanism of Vitamin A might be on the cartilage. This definitely warrants additional research!
The next step we will take is to increase our sample size of wild sharks, sample captive sharks, and (hopefully) get a few samples from sharks with spinal deformities. Then we will compare the vitamin and mineral levels between the three groups and if our data still indicate that captive sharks with spinal deformities have extremely high levels of Vitamin A, we will be able to advise aquaria on the nutritional requirements of their captive shark populations!
In closing, we should not overlook the importance of merely knowing the health status of the wild Sharpnose and Bonnethead. As top predators of the coastal marine ecosystem these two species of shark may serve as important indicators of the health of the ecosystem itself. Knowing their health status now will provide useful comparisons for future studies. Overall, we spent the summer conducting research that can and will be applied to monitor and manage the health of not only captive sharks, but also wild sharks and their marine ecosystems!
Sincerely,
Katie Haman
DVM Candidate 2012
University of Georgia College of Veterinary Medicine
