Setting health standards for sharks

If you want to keep a shark healthy, you must first define what healthy is.

“The gold standard for health is a robust wild shark,” says Greg Lewbart, professor of zoological medicine at NC State’s College of Veterinary Medicine.

While that seems obvious, what isn’t so obvious is how, exactly, veterinarians get data on healthy wild sharks in the first place.

In a study published in the Journal of Zoo and Wildlife Medicine, researchers from NC State and Ecuador took blood samples from juvenile blacktip sharks in the Galapagos Islands so that they could determine blood reference levels for the species.

Reference levels establish health benchmarks for a species, so that veterinarians caring for the animals can diagnose and treat illness. But setting these benchmarks has some unique challenges.

First, just getting the samples is difficult.

The blacktip sharks in the study were in a protected area of the Galapagos, specifically in shallow inlets or lagoons that serve as nurseries for young sharks. Researchers stood in waist-deep water and used nets to create half-moon corrals around the lagoons. Then the juvenile sharks were briefly caught for measurements and sample collection.

“These sharks were probably only two to three years old, and usually under a meter long,” says Olivia Petritz, associate professor of zoological medicine at NC State and corresponding author of the study.

“But even so, it took several humans—wearing thick gloves to protect against their sharp scales—to handle one shark.”

Once the samples are taken, getting them analyzed presents a second set of challenges.

“You can’t run shark blood on normal blood analyzers,” Petritz says.

“Sharks have a very different physiology because they have to handle salt water. For example, in a human being, one measure of kidney health is the blood urea nitrogen, or BUN level. The normal BUN range for humans is between six and 24. In sharks, that number is over 1,000. Blood analyzers made for people will not read those levels.”

The samples had to be shipped to a special facility for analysis. The results show that benchmarks differ significantly between species. For instance, wild blacktips have higher white blood cell counts than wild sandbar sharks, but lower creatine kinase and glucose levels than Atlantic sharpnose and bonnethead sharks.

“Sharks aren’t a monolith,” Petritz says. “Just sampling one species would be like basing health standards for dogs off of foxes.”

“And we have found that there are even variations within the same species based on the season of the year or their location, so it’s important to sample as much as possible,” Lewbart adds.

The research will prove helpful not just to veterinarians caring for captive animals, but also for conservationists.

“This work will also help ichthyologists and non-medical researchers who deal with this species,” Lewbart says. “Sharks are super vulnerable, and in the Galapagos specifically there’s still a lot of pressure on their populations from illegal shark fishing. So anything we can do to help keep them healthy is worth it.”