Bull sharks are having a baby boom along the Texas coast

There have been fewer than 50 shark attacks in Texas in the last century, but you may recall around the Fourth of July weekend this year, two people were sent to the hospital and two others were injured in shark encounters off South Padre Island. 

With that still in mind, there’s new research that would seem to align with what some have suspected: The baby bull shark population is exploding along the Texas coast. 

According to a new study, their numbers have risen by as much as eight times over the past 40 years in estuaries from Sabine Lake to Matagorda Bay. 

For more on this research, Philip Matich, a marine biologist at Texas A&M – Galveston and one of the leaders of this study, spoke with Texas Standard. Listen to the interview above or read the transcript below.

This transcript has been edited lightly for clarity:

Texas Standard: Now, professor, bull sharks, I guess, are a little unique because they’ve evolved to survive in freshwater and even use freshwater nurseries. How does that play into their population growth in Texas waters?

Philip Matich: That’s correct. Across their entire range throughout the world, they use these low-salinity habitats for nurseries, which is where juveniles tend to grow up in lower-risk environments because other shark species aren’t able to go into those ecosystems. And you can imagine that if you’re able to stay in those low-risk environments for longer periods of time during your adolescence, you have a higher likelihood of surviving. 

Why are we seeing these numbers grow? Is it something that’s expected just over time, that their numbers would tend to grow? Or is there any other variable here?

Absolutely. It’s a variety of different factors.

If you’re not familiar with shark management in the United States, it’s only been around for the last 30 years. So in the 1990s, the federal government enacted legislation that protected sharks and managed them more effectively, and states either prior to that or after that followed suit. So, it’s certainly one aspect to consider. 

Another important aspect to consider is that the environments of these nurseries are changing.  

I would presume you’re talking about warmer waters.

Yes, and so the waters around Texas have been warming very slowly but consistently over the last 40 years to the point of more than two degrees Fahrenheit from the 1980s to the 2020s. So it’s getting warmer. 

Two degrees doesn’t seem like it’s that big of an increase, but if you as an animal have to leave a particular area because it gets too cold, if it’s a little bit warmer, it increases the time that you can spend in that area, and it decreases the amount of time that you have to spend in an area that you prefer not to be in, which for these juvenile bull sharks is the Gulf of Mexico.

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It’s my understanding that humans are not a typical part of a bull shark’s diet; however, they are known to be aggressive toward humans. What does this mean for going down to the Gulf for a lot of Texans? And of course, there’s a huge tourism industry there that’s built on a lot of that.

Absolutely. I think over the last 10 to 20 years, there’s been a lot of questions about what the implications of recovering shark populations will look like, specifically in terms of interactions with humans. 

It’s not clear right now what the results of this increasing abundance of juvenile bull sharks mean for adult bull sharks. The stock of bull sharks in the Gulf of Mexico hasn’t yet been assessed, so we’re not sure if these increases are actually translating to more large bull sharks, or if this is just something we’re seeing among the smallest ones and that the consequences are relatively small in terms of increasing adults.

How might this affect the overall Gulf ecosystem if we have a lot more baby bull sharks along the Texas Gulf Coast and its estuaries?

That’s a great question, and it’s a very complex question because we know that any one of our estuaries has dozens of different species of fish and mammals and reptiles and birds, and everything is coexisting. 

If you have an increase in one predator population – say, a species of shark – does that mean that it’s going to negatively impact maybe a prey population? Or maybe it’s going to be increasing its competition with another predator species – say, maybe alligators or some type of wading birds. 

We really don’t know the answer to that question because concurrently, while these sharks have been slowly increasing in abundance through time, we’re also seeing changes in the abundance of other species, particularly some of the fishes that humans rely upon. 

You could certainly maybe draw a connection that increasing sharks means they’re eating more of these fish, but we also know that there’s an increased number of people that live in the area so maybe there’s more people catching these fish. 

Also, with this increasing water temperature, some of these species — one good example of this is southern flounder — their numbers are decreasing, in part because they’re just not reproducing as effectively because of these warmer waters.

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