Texas A&M University-Corpus Christi researcher studies endangered smalltooth sawfish DNA
Decades after the endangered smalltooth sawfish disappeared from Texas coastlines, researchers at Texas A&M University-Corpus Christi aim to find out how many remain in the U.S.
A century ago, it would not have been unusual to come across smalltooth sawfish near Bob Hall Pier in Corpus Christi. Historically, the species could be found from North Carolina to Texas.
But populations declined dramatically in the 20th century. Exactly how many smalltooth sawfishes there might have been before they began disappearing and exactly how many there are today is hard to estimate. But they aren’t found any more in Corpus Christi.
The last confirmed record in Texas was in Aransas Bay in 1984.
Decades after the species disappeared from much of its historic habitat, the smalltooth sawfish earned federal protection as an endangered species in 2003.
Today, smalltooth sawfish are only regularly found in southwest Florida in the U.S.
To determine what impact federal protection has had on the species, A&M-Corpus Christi researchers aim to find out current and historic population sizes.
The university's Marine Genomics Lab has received more than $375,000 from the Shark Conservation Fund to use DNA sequencing technology to estimate the population size of the smalltooth sawfish.
Post-doctoral researcher Dominic Swift is the lead researcher on the smalltooth sawfish project.
“It has been under the Endangered Species Act for a while, but they actually don’t have much information about whether any of these changes have been beneficial in increasing its abundance,” Swift said.
To take a species off the endangered and threatened species list, authorities have to be able to show that populations have increased.
“But the problem with that sort of goal post is we almost never know what the number was in the past,” associate professor and marine biology graduate program coordinator David Portnoy said. “We usually don’t realize we need to know that until the crash.”
Smalltooth sawfish are a type of ray, but they resemble sharks. They are known for their long, flat snouts edged with teeth. A smalltooth sawfish can grow to over a dozen feet long and weigh several hundred pounds.
Scientists produced a full genome for the species in 2019.
“If you have a really good reference genome – which is basically a collection of all the different DNA sequences of a species – that can be used in a really robust way to do different types of analyses,” Swift said.
The project aims to use DNA analysis to assess the relationships between individual smalltooth sawfish, such as whether they are parents and offspring, siblings or cousins.
If you can determine how many of each different type of relationship there is within the population and you also understand how the population grows, such as when and how often individuals reproduce and how many offspring they can have, you can estimate the population size, Swift said.
“Really small populations have a lot of related individuals because there’s only a limited number of parents available,” Portnoy said. “Large populations have relatively few related individuals because there’s loads of parents.”
Because there are no accurate population counts from before the species became endangered, genetic analysis is the best way to find out how many there might have once been, Swift and Portnoy said.
“We’ll first get an idea of what is it currently and then we’ll get an idea of what was it in the past before the population decline occurred,” Swift said. “That allows the sawfish team to understand what our baseline was and where we are now and how far away we are from what we really need to be.”
In Florida, the National Oceanic and Atmospheric Administration's Smalltooth Sawfish Recovery Team is working to recover the U.S. population through research, outreach and education. Swift plans to set up a monitoring tool for the group to continue incorporating new samples and assess how recovery is progressing in the future.
Recovery is a slow process, Swift said, because smalltooth sawfish grow and mature slowly and reproduce infrequently, like other sharks and rays.
The story of the smalltooth sawfish is shared by many other endangered and threatened sharks and rays, Portnoy and Swift said, including species that are still present in Texas waters and impacted by fishing.
“More broadly, what has led to the problem for sawfish is also a problem for hammerhead sharks and sandbar sharks and other numbers of species that follow the same sort of patterns,” Portnoy said.
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This article originally appeared on Corpus Christi Caller Times: A&M-Corpus Christi researcher studies endangered sawfish DNA
