The Oklahoma Aquarium is home to the world’s largest collection of bull sharks in the world. Ten of the “most dangerous sharks known to man” inhabit a 380,000-gallon saltwater tank and tunnel, along with three nurse sharks. This immersive exhibit allows visitors the chance to walk through tunnels beneath and alongside some of the most beautiful and deeply misunderstood creatures in the sea.
Bull Sharks (Carcharhinus leucas)
We have male and female bull sharks at the Oklahoma Aquarium, all of which weigh about 250 pounds. Our bull sharks eat 1-2% of their body weight in fish, shellfish, and squid. In the ocean, these carnivores may also eat mammals like seals or dolphins.
Bull sharks are known as “the most dangerous” shark in the world because of the number of shark attacks on humans. But despite this reputation, bull sharks do not have it out for people; we know this for a few reasons. One is that all sharks have the ability to detect electricity in the water using a series of specialized, jelly-filled organs called ampullae of Lorenzini. Since bull sharks often live in murky waters, they will attack any electricity they sense, so they likely cannot and do not differentiate between a person and a large fish.
When our divers clean the shark tank, one of their jobs is to vacuum up the shark teeth that decorate the floor. Sharks lose approximately 30,000 teeth in a lifetime. In addition to the teeth inside their mouth, sharks have a form of modified teeth on their skin! These modified, tooth-like structures are known as dermal denticles, and are believed to help sharks swim faster and quieter by reducing drag and turbulence. All condrichthians, or cartilaginous fish, have dermal denticles and skeletons made up of cartilage instead of bone. Condrichthians encompass all species of sharks, rays, skates, and chimaeras.
Amongst shark species, bull sharks are one of the most unique. They are the only shark that can live in both freshwater and saltwater! They can do this because their rectal glands can osmoregulate; that is they can control the salt content of their blood, which is important because it keeps them from losing water to the environment around them,6 regardless of their location. As pups, they cannot yet osmoregulate, and for that reason, female bull sharks must birth their pups in freshwater. Sometimes, bull sharks will travel very far into freshwater; they have been found as far as 1,500 miles up the Mississippi River and 2,500 miles up the Amazon River.
Along the bottom of the tank you may notice three sharks. These docile creatures are nurse sharks (Ginglymostoma cirratum), and they often congregate around the pumps along the bottom of the tank to receive fresh, oxygenated water. This clean, oxygen-rich water makes their lives easy because they utilize buccal pumping to breathe. Buccal pumpers use their cheek, or buccal, muscles to pull water into their mouths and over their gills for gas exchange. Breathing this way means they can spend their time relaxing near the sea floor. If nurse sharks were like bull sharks they would need to swim all the time to breathe or else they would actually drown! Swimming forces the water to ram up against a bull shark’s gills for gas exchange; without movement bull sharks and other ram ventilators have no way of forcing water through their gills.
No one really knows where nurse sharks got their name, but some people believe it is because they sound like nursing babies when they suck up their food. Their diet consists of shrimp, squid, and small fish, as well as crunchier prey like mussels, clams, shellfish, and occasionally coral. Rather than having razor-sharp teeth, they simply have strong, crushing jaws.They hunt for their food at night and spend their days piled up in groups, usually in the same spot each day. They live in the eastern Pacific and western Atlantic oceans, where they are a common and harmless sight for scuba divers.
Having the world’s largest collection of bull sharks in a controlled environment and clear water provides ideal circumstances for filming and research. Our sharks have received a lot of media attention from multiple networks including the Discovery Channel and the BBC. Our biology staff examines the sharks to track their weight, length, and blood gases, as well as to check for parasites; a common shark parasite is isopods (like the one you’ll see in our discovery caves). From this research we learned that starting with younger bull sharks and performing exams on a routine basis reduced their stress levels. Preventing stress in exams is important because lower stress levels make for healthier sharks.
In addition to research that helped other sharks, our sharks also participate in research to protect people. In collaboration with the National Oceanic and Atmospheric Association (NOAA), the Oklahoma Aquarium’s bull sharks were used to improve the government’s Tsunami Warning System. NOAA produces mooring lines which are ropes that hold together buoys. The Tsunami Warning System relies on these mooring lines hold buoys in places because their buoys relay important information about inclement weather, such as incoming storms and tsunamis. Sometimes, curious sharks in the ocean will encounter mooring lines and bite them, cause them to break, and render previously attached buoys useless. Since bull sharks have the strongest bite force of any shark, they set the highest standard for mooring line toughness. Therefore, researchers placed mooring lines of different thicknesses in the tank with our bull sharks to observe which lines could withstand a bull shark’s bite.
Currently, bull sharks are listed by the IUCN Red List as “near threatened,” and there is no research to indicate how their population sizes are changing. What we do know is that many species of sharks, including bull sharks, are disproportionately affected by human activity. Since bull sharks also frequent rivers and estuaries, they are more susceptible to the detriments of accidental fishing and habit modification. Though bull sharks are generally the victims of bycatch, they have also been exploited for their fins, skin, liver oil, and flesh. Shark fin is considered a delicacy by some and many species of sharks, including bull sharks and nurse sharks, are threatened by overfishing. As apex predators, or predators at the top of the food web, we also need sharks to manage the population sizes of their prey. Otherwise, fish that are lower in the food web would use up too much of our ocean’s resources, like plankton and algae.
Furthermore, one of the greatest challenges shark populations face is their reputation. Sensationalized shark attacks in the media and film have created undue fear for many sharks and endangered species are sometimes hunted and killed for this reason. One way to challenge your own shark fears, if you have any, is to interact with small sharks here at the Oklahoma Aquarium! Click here to learn about Touch Time in our EcoZone.
- One reason bull sharks are so jaw-some is because they have the strongest bite force of any shark: they apply 8,702 pounds of pressure per square inch in each bite.
- With about 50 rows of seven teeth, bull sharks can have up to 350 teeth in their mouth at any given time.16
- Like dolphins, nurse sharks can be trained using positive reinforcement.
Shark Feeding Show
Weekly shark feeding shows take place on Mondays and Thursdays at 1:30 p.m.
Written by Alyssa Rodriguez, February 2019.