Pregnant Shark birth tracking technology provides key data for species protection
Protecting newly born shark pups crucial for balancing ocean ecosystem
Peer-Reviewed PublicationIMAGE: INSERTION OF THE BIRTH-ALERT-TAG (BAT) VIA A SPECIALIZED APPLICATOR INTO THE CLOACAL OPENING OF A PREGNANT TIGER SHARK view more
CREDIT: CREDIT: TANYA HOUPPERMANS / BLUE ELEMENTS IMAGING
Most people find sharks threatening. Who doesn’t have an image in their mind of a menacing shark fin racing through the ocean in search of its next meal?
But it is the shark that is threatened.
According to Defenders of Wildlife, a national nonprofit dedicated to protecting imperiled species, 75% of shark species are threatened with extinction and up to 73 million sharks are being killed each year for their fins.
Habitats that were once secure places for sharks to give birth have also been affected. And the fact that sharks have long gestation periods, giving birth to relatively few young, and maturing late in life — complicates efforts at repopulation.
And that’s a problem.
In a new paper published today (March 1) in Science Advances, authors James Sulikowski, a professor at Arizona State University and Neil Hammerschlag, a marine ecologist at the University of Miami, describe a new technology they developed capable of remotely documenting the location and time of birth of shark pups. This type of data will enable scientists to create ways to protect the sharks’ most vulnerable habitats, where they give birth.
“If they (the mother sharks) don't have that suitable habitat, then their babies won't be able to grow up. And if babies don't grow up, we have no more sharks and literally, the ocean ecosystem would collapse,” explained James Sulikowski, senior Global Futures scientist at Arizona State University and director of the Sulikowski Shark and Fish Conservation Lab at ASU’s New College of Interdisciplinary Arts and Sciences.
The device is making waves in the scientific community — and for good reason.
“We've been trying to do this since we started studying sharks. This is our holy grail. We have really advanced shark science, 20, 30, 40 years,” said Sulikowski. “This novel, satellite-based technology will be especially valuable for the protection of threatened and endangered shark species, where protection of pupping and nursery grounds is a conservation priority.”
The paper outlines the deployment and results of an intrauterine satellite tag on two highly mobile sharks — a scalloped hammerhead and a tiger shark –,to detect when birth occurs, leading to its name, birth-alert-tags (BAT).
Here’s how BAT works.
First the BAT is inserted into a pregnant shark. The egg-shaped technology is approximately 2 inches long and 1 inch wide. When the shark gives birth, the BAT pops out along with the pups and reaches the ocean surface. Once there, the device switches to transmitter mode sending messages announcing the time and location of the birth.
The BAT has already yielded remarkable results. Where it was once assumed that sand sharks gave birth inland, the scientists have learned that they are most comfortable having their pups in abandoned shipwrecks on the ocean floor.
“It was a total surprise,” Sulikowski said. “For most shark species we have no idea where they give birth or how far they must travel to habitats that are essential to their survival.”
Once habitats are discovered, efforts will be made to protect those areas, either by creating sanctuaries or expanding areas already set aside for this purpose.
The ultimate goal is to go global with the BAT.
Sulikowski wants to create a worldwide network of shark scientists to determine areas that are important to sharks and figure out how to protect them.
Persistence pays off
Sulikowski is enjoying his current success. “We've had every sort of failure that can happen,” he said. “We had battery failures. We had firmware failures, we had antenna failures. I felt like giving up multiple times. But thanks to my co-author, Neil Hammerschlag, we kept forging ahead and we didn't give up.”
“Honestly, it feels incredible to have created technology that is going to revolutionize the way that we study sharks,” Sulikowski added.
Image of the Birth-Alert-Tag (BAT)
CREDIT
Credit: James Sulikowski
In a new study, researchers used new technologies to remotely document, for the first time in the wild, the location and timing of shark birth. Ultrasounds were used to identify pregnant sharks. During pregnancy in sharks, the entrance to the uterus remains semi-permeable to allow for water exchange between the uterus and outside. So, with the aid of a specialized applicator and guided by the ultrasound, the team inserted a new type of satellite tag through the shark’s cloaca (akin to a vaginal opening) and into its uterus, where the tag was then deposit among developing embryonic sharks. Named the Birth-Alert-Tag (BAT), this new satellite tag remained inside the uterus, along with the developing shark pups, until the mother shark gave birth and expelled the newborn pups, along with the BAT, into the surrounding water. The BAT then floated to the surface and transmitted to satellites the location of where the shark birth took place. The first of its kind, the BATs were successfully deployed in a tiger shark and scalloped hammerhead shark, documenting the location birth.
CREDIT
Infographic by Bianca Rangel. Shark by Kelly Quinn / Canvas of the Wild.
JOURNAL
Science Advances
ARTICLE TITLE
A novel intrauterine satellite transmitter to identify parturition in large sharks
ARTICLE PUBLICATION DATE
1-Mar-2023
‘Chunky dunk?’ Cleveland’s prehistoric sea monster may have been shorter, stouter, than once believed
Case Western Reserve University scientist PhD student applies new calculations to reveal downsizing and chunky details about species from Devonian Period
Peer-Reviewed PublicationIMAGE: GRAPHICAL ABSTRACT SHOWING THE RELATIVE SIZE OF DUNKLEOSTEUS COMPARED TO A HUMAN FIGURE--BEFORE AND AFTER THE NEW CALCULATIONS. view more
CREDIT: RUSSELL ENGELMAN/CASE WESTERN RESERVE UNIVERSITY
CLEVELAND—About 360 million years ago, in the shallow subtropical waters above what is now the city of Cleveland, an armor-plated fish many believed to be up to 30 feet long ruled the seas.
The species Dunkleosteus terrelli was Earth’s first vertebrate “superpredator” and lived during the Age of Fishes (Devonian Period)—when North America was near the latitude of what is now Rio de Janeiro.
But in nearly 150 years of research since fossilized remains of the prehistoric big fish were discovered on the shores of Lake Erie in 1867, scientists may have made some incorrect assumptions about Dunkleosteus’ size and shark-like shape.
In research published this month, a Case Western Reserve University scientist suggests the length of this prehistoric predator may have been greatly exaggerated—that it was much shorter and chunkier.
Cleveland mascot and Ohio’s top fossil fish
“Dunkleosteus is already a strange fish, but it turns out the old size estimates resulted in us overlooking a lot of features that made this fish even stranger, like a very tuna-like torso,” said Russell Engelman, a Case Western Reserve PhD student in biology and lead author on a study published in the journal Diversity in February. “Some colleagues have been calling it ‘Chunky Dunk’ or ‘Chunkleosteus’ after seeing my research.”
Engelman said he recognizes downsizing the iconic Dunkleosteus may not be welcome news because the big fish “is essentially Cleveland's mascot when it comes to paleontology” (The species even had a Twitter account for a few years). As a native Clevelander, he said he originally had similar feelings.
Most research on Dunkleosteus is based on specimens in the Cleveland Museum of Natural History, which has the largest and highest quality collection of Dunkleosteus remains in the world. And its name honors both a former museum curator (David Dunkle) and a local business owner (Jay Terrell) who discovered the fossilized species.
Dunkleosteus is such a homegrown icon that in 2020, the Ohio General Assembly declared Dunkleosteus terrelli the state fossil fish.
Even so, little research has been done on the fish since the 1930s, Engelman said.
“Without reliable size estimates, not much could be said about Dunkleosteus scientifically beyond ‘look at the big, scary fish!’” Engelman said. “These length estimates were an example of something that just slipped by everyone's notice because it was assumed this fish has been well-studied.”
Short head, short body
Most estimates of the species’ length weren’t based on hard evidence, Engelman said.
That’s because Dunkleosteus was a type of extinct fish called an arthrodire. Unlike modern fishes, arthrodires like Dunkleosteus had bony, armored heads but internal skeletons made of cartilage. This means only the heads of these animals were preserved as fossils, leaving the size and shape a mystery.
The new study proposes estimating the length based on the 24-inch-long head, minus the snout—considered a way to measure that’s consistent among groups of living fishes and smaller relatives of Dunkleosteus known from complete skeletons.
“The reasoning behind this study can be summed up in one simple observation,” Engelman said. “Short fish generally have short heads and long fish generally have long heads.”
Based on that method, Engelman concluded Dunkleosteus was only 11 to 13 feet long—much shorter than any researcher had proposed before.
‘Wrecking balls’ of the deep
“Dunkleosteus has often been reconstructed assuming it had a body shape like a shark,” Engelman said.
But a shorter body and shape of the body armor also meant Dunkleosteus was likely much chunkier.
“An 11-foot Dunkleosteus is essentially the same weight as a 15-foot great white shark,” Engelman said. “These things were built like wrecking balls. The new proportions for Dunkleosteus may look goofy until you realize it has the same body shape as a tuna…and a mouth twice as large as a great white shark.”
These new size estimates also help put Dunkleosteus in a broader scientific context. Dunkleosteus is part of a larger evolutionary story, in which vertebrates went from small, unassuming bottom-dwellers to massive giants.
“Although the reduced sizes for Dunkleosteus may seem disappointing,” Engelman said, “it was still probably the biggest animal that existed on Earth up to that point in time. And these new estimates make it possible to do so many types of analyses on Dunkleosteus that it was thought would never be possible. This is the bitter pill that has to be swallowed, so that now we can get to the fun stuff.”
Patricia Princehouse, associate director of CWRU's Institute for the Science of Origins said it was exciting to see the new work.
"This fresh take on the legendary Dunkleosteus 'sea monster' shows there's still lots of brand-new breakthroughs waiting to be discovered in the world of paleontology, even with famous species," Princehouse said. The multidisciplinary institute initiates and conducts scientific research in origins-related sciences and has promoted work undertaken by Engelman and other students.
Engelman conducted his research under advisor Darin Croft, professor of anatomy at the Case Western Reserve School of Medicine, who also advises students in biology in the College of Arts and Sciences.
JOURNAL
Diversity
ARTICLE TITLE
A Devonian Fish Tale: A New Method of Body Length Estimation Suggests Much Smaller Sizes for Dunkleosteus terrelli (Placodermi: Arthrodira)
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