Our seas are full of every type of shark imaginable. They come in all different shapes, sizes, colors, and patterns. They eat everything from the tiniest plankton to juvenile whales, swim thousands of miles and jump high into the air, and live in every ocean on the planet, from the surface all the way down to the sea floor. One of these crazy types of sharks is the bull shark. Although famous mostly for its fearsome nature, the bull shark is also cool for another reason; it is one of the only shark species that can live in both saltwater and freshwater!
Bull sharks mainly use this trait to protect their babies from predators. Mother bull sharks give birth to their young in estuaries, where fresh water meets the sea, like at the mouth of a river or a stream. Estuaries are safe because marine predators, including other types of sharks, cannot enter and hurt the young. The water is also often warmer and shallower than other potential birthing sites, overall making it a safe place for baby sharks, called pups, to grow up. Because these estuaries are often filled with bull shark pups from many different mothers, scientists have nicknamed them nurseries.
A new nursery for bull shark pups was recently discovered in Chetumal Bay in the Caribbean off the coast of Mexico [1]. Its shallow waters are especially abundant in food for bull shark pups, allowing many young to start their lives here before heading off into the ocean when they get bigger. In addition, Chetumal Bay is special because many mother bull sharks come here multiple times to give birth. And pups born here often return to have their own babies. Because sharks do not give any parental care to their young, the baby sharks all live together by themselves. Imagine a daycare or preschool with no adults! But unlike humans, bull shark pups are born with a full set of teeth and strong bodies, making them small but ferocious from the start. They are able to hunt for their own food, like crabs, fish, and seabirds, and even eat other baby bull sharks when they get really hungry. Yikes!
The discovery of the Chetumal Bay nursery is also important because bull sharks are currently considered a threatened species with their population numbers declining worldwide. Bull sharks are struggling mainly due to human influence. Climate change is destroying their habitats, overfishing is decimating their food sources, and many bull sharks are murdered by people just for their fins. Studies have also shown that young bull sharks are at an even higher risk because they are often killed in coastal regions as bycatch. Bycatch are any animals caught by accident in nets, meaning they are wasted. As a result, scientists predict that bull shark numbers will continue to decline unless action is taken.
Fortunately, Chetumal Bay is already a marine protected area so baby bull sharks are relatively safe from human influence there. Still, many of them are caught by fishermen outside the bay when they are older, demonstrating the need for more widespread conservation efforts. And we must continue to advocate for other nurseries to be protected too so that bull shark pups have a chance to grow up and become the fearless, amazing creatures they were born to be. Who knows, maybe you’ll even be lucky enough to see one of these apex predators with your own eyes someday! But only if the right conservation steps are taken now to protect their future.
1. Blanco-Parra, Sandoval-Laurrabaquio-Alvarado, Díaz-Jaimes, et al. “Evidence of a nursery
area for bull shark, Carcharhinus leucas (Müller y Henle, 1839) in the Mesoamerican Reef System region.” Environ Biol Fish 105, 1193–1202 (2022). https://doi.org/10.1007/s10641-022-01338-1
