Juvenile bull sharks thrive in Texas and Alabama bays because the Gulf of Mexico warms

In late spring, estuaries along the U.S. Gulf Coast teem with newborn fish and other marine life. While some species have struggled to adapt to the region's rising water temperatures in recent times, one species is prospering: juvenile bull sharks.

We study this iconic shark species, named for its powerful body and matching disposition, within the Gulf of Mexico. Over the past twenty years, we’ve got Number of bull shark pups in Mobile Bay has increased fivefoldAlabama, and an identical increase in several river mouths in Texasas our latest study shows.

Despite the bull shark's fearsome status, baby bull sharks will not be a cause for concern for humans in these waters.

While adult bull sharks are occasional unprovoked attackBaby bull sharks haven’t yet fully developed the abilities they should hunt larger prey. And they’re still much more prone to be killed of bees, wasps or snakes than of sharks.

The fascinating lifetime of a young bull shark

Most sharks are purely marine sharks and spend their entire lives within the sea. Bull sharks, nonetheless, are one in all the a handful of shark species that use freshwater environments as breeding grounds.

Baby bull sharks found within the Alabama River75 miles north of the ocean, and up the Mississippi to Illinois. They have evolved to tolerate fresh water by having a lower need for salts and urea of their bodies in comparison with marine sharks and actively absorbing more salts through their food and their gills.

In Texas, populations of young bull sharks are Increase in river mouths equivalent to Galveston Bay and Sabine Lake over the past 40 years, especially where rivers equivalent to the Trinity, Sabine and Neches intersect with these ecosystems. These areas can provide protection from predators equivalent to larger sharks.

The presence of bull sharks in these estuaries also contributes to their health and stability.

Because bull sharks ceaselessly migrate between freshwater and marine ecosystems, they will act as mobile links between these two aquatic environments. Bull sharks often feed in a single environment, equivalent to saltwater, after which rest and excrete nutrients in freshwater bays. Feeding and resting in numerous locations may improve the resilience of those ecosystems to disturbances equivalent to warmer weather conditions, because if one habitat is disturbed, the opposite is preserved.

Food webs, like spider webs, are connected by many intersecting threads. The more threads, the stronger the online. Bull sharks' use of freshwater and marine habitats increases the variety of these threads through their predator-prey interactions, thereby strengthening the ecosystem.

The waters are warming

As the planet warms, the temperatures of the coastal seas are also rising. In the Gulf of Mexico, water temperatures are increased by greater than 3 degrees Fahrenheit (greater than 1.5 degrees Celsius) attributable to climate change.

On a worldwide scale, warming waters are harming more fish species than they’re helping. Higher temperatures increase food needs and stress levels, while making fish more at risk of disease and reducing the probabilities of survival of their young. Quite a lot of fish populations within the Gulf of Mexico, including mullet and flounderhave declined as warmer conditions affected their spawning.

At the identical time, the waters utilized by young bull sharks have expanded, partly attributable to this warming, making a dynamic habitat.

To understand how sharks use dynamic habitats, it is simple to catch them with nets and measure the characteristics of their environment. In our sample data, we found that average annual water temperatures along the coasts of Alabama and Texas increased similtaneously bull shark populations increased.

In the Alabama coast, we found that the relative abundance of bull shark pups quintupled within the last 20 years. Slight temperature increases during this era were the very best explanation for this population increase.

Of all of the temperatures recorded on this study, no maximum temperature threshold was found for bull shark pups. Until now, not less than since 2003, the rule for bull shark pups has been “the warmer the better.”

We observed an identical trend along the Texas coast from Sabine Lake to Matagorda Bay, where warming estuaries led to a rise within the population of bull shark pups. as much as eight times over the past 40 years. Warmer waters allowed young bull sharks to remain of their natal mouths longer during their first 12 months before wintering within the Gulf of Mexico, increasing their possibilities of survival to the subsequent life stage.

Overall, our recent studies show that warming waters are currently useful for juvenile bull sharks. But identical to your favorite dessert, an excessive amount of of a great thing may be harmful.

All animals, including bull sharks, have maximum and minimum temperatures at which they will function. When temperatures get too hot or too cold, it will possibly cause problems, whether through direct stress to the shark's bodily functions or to its ecosystem as an entire.

Some of our previous work from Florida shows that bull shark pups will leave coastal nursery areas in response to episodic cold to avoid cold stress. Sharks that didn’t leave died. The same could also be true for warm temperatures, although our research indicates that conditions within the Gulf of Mexico haven’t yet reached that time.

A changing world

It is evident that climate change is altering coastal ecosystems. Our work shows that juvenile bull sharks are directly benefiting, but how the observed population growth will affect other species in coastal estuaries stays to be seen.

The rise of bull sharks may affect other fish speciesincluding bull shark prey equivalent to mullet, drum, herring and catfish. More bull sharks could ultimately mean fewer of the fish that individuals rely on. In warmer water, sharks use more energy.

Ultimately, tracking changes within the distribution of species like bull sharks over time stays critical to understanding future changes in fish populations and the health of our coastal ecosystems.