Nerding Out for Nurse Sharks!
By Ethan Dewald
Picture from Bimini, Bahamas
Lurking under a ledge. Sashaying through the seagrass. Resting on the reef. Wandering in the water column. Meandering through the mangroves. All of these describe ways you could encounter the nurse shark, one of the most recognizable shark species found in the waters around Florida. Nurse sharks lack the sharp teeth that most people associate with sharks, and this is because they feed on invertebrates and small fish, which are crushed by the nurse shark’s bony mouth plates.
Sometimes we see these sharks hiding under coral ledges or in caves!
Another cool thing about these sharks is that they do not need to keep swimming to breathe! Instead, they can rest facing the current and actively pump water over their gills, which often makes them appear to be sleeping when you encounter them in the field. Nurse sharks are nocturnal, meaning that they are more active at night rather than during the day. They are often incredibly docile individuals, and are not overly afraid of humans, allowing for close encounters with divers or snorkelers. I have had nurse sharks rest on top of my back while freediving on sand flats and near wrecks; they have no sense of personal space!
Since nurse sharks don’t need to swim to breathe, we often see them resting on the bottom.
Nurse sharks are a common sighting during many of the trips that students participate in while staying at MarineLab. Subadults and adults can be found on many of the coral reefs in the Florida Keys National Marine Sanctuary that we visit during our Coral Reef Ecology field trips. Juvenile nurse sharks can often be found resting amongst the mangrove roots and hunting in the seagrass beds of Florida Bay and Largo Sound that we visit with our Seagrass and Mangrove Ecology field trips. Nurse shark juveniles remain in shallow mangrove and seagrass habitats for the first part of their life because they are small and flexible due to their cartilaginous skeletons so they can maneuver in the tight spaces of the mangrove roots that larger sharks cannot swim through. This allows the baby sharks to avoid larger predators that would otherwise hunt them, allowing them to focus on learning how to be a shark. The seagrass and mangroves also serve as a nursery habitat for many species of fish and crustaceans that baby sharks can feed on while they are protected. Any of our other field trips to locations near coral reefs and seagrass and mangroves have a similar likelihood of a nursey making a guest appearance.
This juvenile nurse shark was only two feet long when we saw it in a seagrass bed!
Often, people are afraid of sharks and being in the water with them thanks to Hollywood classics like Jaws, The Shallows, and more recently, The Meg. As entertaining as these films may be, it is important to remember these are works of fiction, and not indicative of how sharks act in the natural world. In reality, sharks are much more afraid of us than we are of them. Sharks are right up near the top of their respective underwater food chains, and their presence indicates a healthy underwater ecosystem. I always hope to show students that come to MarineLab a shark in the field, because the most life-changing and inspiring moments of my life and career have come while diving with sharks. There’s no need to be afraid of sharks in the water. Instead, embrace the fact that two apex predators (you and the shark) share the water as equals. If there’s a shark in the water, I will be swimming toward it and not away from it!
Sometimes nurse sharks are masters of camouflage, like this one hiding under mangrove roots!