In late spring, estuaries along the U.S. Gulf Coast come alive with newborn fish and other sea life. While some species have struggled to adjust to the region’s rising water temperatures in recent years, one is thriving: juvenile bull sharks.
We study this iconic shark species, named for its stout body and matching disposition, along the Gulf of Mexico. Over the past two decades, we have documented a fivefold increase in baby bull sharks in Mobile Bay, Alabama, and a similar rise in several Texas estuaries, as our new study shows.
Despite the bull shark’s fearsome reputation, baby bull sharks are not cause for concern for humans in these waters.
While adult bull sharks are responsible for an occasional unprovoked attack, baby bull sharks haven’t fully developed the skills needed to hunt larger prey. And you’re still far more likely to be killed by bees, wasps or snakes than sharks.
The fascinating life of a young bull shark
Most sharks are fully marine and spend their entire lives in the ocean. Bull sharks, however, are one of a handful of shark species that use freshwater environments as nurseries.
Baby bull sharks have been found in the Alabama River, 75 miles north of the ocean, and up the Mississippi River as far as Illinois. They have evolved to tolerate fresh water by reducing the need for salts and urea in their bodies compared to marine sharks, and actively taking in more salts through their food and across their gills.
In Texas, young bull shark numbers have been increasing in estuaries like Galveston Bay and Sabine Lake over the past 40 years, particularly where rivers like the Trinity, Sabine and Neches intersect with these ecosystems. These areas may offer protection from predators, such as bigger sharks.
In 2012-2023, Texas reported seven shark bites, and Alabama reported two, none of them fatal, according to the International Shark Attack File. After white sharks and tiger sharks, bull sharks have had the most reported unprovoked shark attacks on humans globally.
Albert Kok via Wikimedia Commons, CC BY-SA
The presence of bull sharks in these estuaries also contributes to their health and stability.
Because bull sharks frequently move between freshwater and marine ecosystems, they can act as mobile links that connect these two aquatic environments. Bull sharks often feed in one environment, salty water for example, and then rest and excrete nutrients in freshwater bays. Feeding and resting in different locations can improve the ability of these ecosystems to withstand disturbances like warming weather conditions, because if one habitat is disturbed, the other is still supported.
Like a spider web, food webs are connected by many intersecting threads. The more threads, the stronger the web. The use of both freshwater and marine habitats by bull sharks increases the number of these threads through their predator-prey interactions, thereby strengthening the…
