Recent research reveals that their numbers in Alabama’s Mobile Bay have risen fivefold over the past two decades, and similar trends have been seen in Texas estuaries like Galveston Bay, according to a new study.

Estuaries as nurseries

Three of the researchers of these studies, James Marcus Drymon and Lindsay Mullins of Mississippi State University and Philip Matich of Texas A&M University, wrote in The Conversation that bull sharks are one of the few shark species that can tolerate freshwater and use rivers and estuaries as nurseries. Young bull sharks have been spotted as far inland as the Alabama and Mississippi Rivers, adapting to fresh water by regulating their salt intake. 

These estuaries provide protection from predators and help support the sharks’ growth. Bull sharks, being highly mobile, connect freshwater and marine environments, benefiting the overall ecosystem. By moving between these habitats, they contribute nutrients and help maintain the balance of the ecosystem, especially as environmental conditions change.

Unlike adult bull sharks, which are occasionally involved in unprovoked attacks, baby bull sharks pose little threat to humans. They lack the hunting skills of their older counterparts and are still developing the ability to pursue larger prey.

Warmer waters

As global temperatures rise, the Gulf of Mexico has warmed by over 3°F (over 1.5°C), and while many species are struggling to cope, baby bull sharks have benefited. The researchers state that warmer waters have expanded their habitat, allowing them to remain in the estuaries longer, increasing their chances of survival. They have observed up to an eightfold increase in juvenile bull sharks in Texas over the last 40 years.

However, while warming waters are currently supporting their growth, future temperature extremes could pose challenges. Research suggests that both cold and hot temperatures may stress bull sharks, potentially disrupting their ecosystems. Monitoring these changes is crucial to understanding the long-term impact of climate change on bull shark populations and other coastal species, the researchers said.