by If you have a baby, or have come across one in the past year, you’ve surely experienced the song “Baby Shark”. Somehow, every child seems to know this song, but scientists know very little about where and when sharks give birth. The origin of these famous sharks is still largely a mystery.
Many of the large, iconic shark species – such as great whites, hammerheads, blue sharks and tiger sharks – traverse hundreds or thousands of ocean miles each year. Because they are so vast, much of shark life, including their reproductive habits, remains a mystery. Scientists have struggled to figure out exactly where and how often sharks kill, the length of their gestation period, and many aspects of the birthing process.
He is a Ph.D. I’m a student studying shark ecology and reproduction and I’m on a team of researchers hoping to answer two important questions: Where and when do sharks live?
Innovation is needed
Until recently, the technology to answer these questions did not exist. But marine biologist James Sulikowski, a professor at Arizona State University and my research mentor, changed that. He developed a new satellite tag called the Birth-Tag with the help of technology company Lotek Wireless. He has no stake in the company. Using this new satellite tag, our team is working to determine where and when tiger sharks give birth and are demonstrating a proof of concept for how scientists can do the same for other species big sharks.
The Birth Tag is a small oval device that we insert into the uterus of a pregnant shark, where it will remain dormant and hidden among the fetal sharks during pregnancy. This type of tag has never been used on sharks before, but similar implanted tags have been used to determine the birthing sites of land mammals, such as deer, for many years. When a tagged mother shark gives birth, the tag will be expelled along with the babies and will float to the sea surface. As soon as it detects dry air, the tag transmits its location to a passing satellite, which sends that location and the time of transmission back to our lab. Once we download this information, we know where and when that shark was born.
After years of fine-tuning this new technology, we launched the first phase of the study in December 2019 and began using the tags. When the Institutional Animal Care and Use Committees at Arizona State University and the University of Miami, as well as the government of the Bahamas, approved the study, we set out to find some tiger sharks. To do this, our team of researchers from the Sulikowski Shark and Fish Conservation Laboratory and the Shark Research and Conservation Program at the University of Miami led by marine biologist Neil Hammerschlag, traveled to the crystal-clear waters of Tiger Beach off the Grand Bahama Island to refer tiger sharks.
Up close with an apex predator
Tiger Beach is a hot spot for female tiger sharks of many life stages, including large pregnant individuals. These pregnant females may be congregating in the warm, calm waters of Tiger Beach to seek refuge and speed up their labor.
The high number of pregnant sharks in this small area makes it much easier to find one, but actually catching a larger 10-foot shark and bringing it to the boat is no easy task. We use backlines when fishing for sharks, and it can take several hours to safely catch one of these powerful creatures, haul it in by hand and secure it next to the boat.
When we catch a female tiger shark, we first do some length and girth measurements to get an idea of her general health and see if she is sexually mature. Then we check for bite marks, which are evidence of a recent mating event.
After gathering this baseline information, we rotate it upside down to lure it into a trance-like state called tonic immobility. Tonic immobility is a natural reflex in many sharks that maintains a state of physical inactivity. This keeps the powerful shark calm and still for the most exciting part of the workup, the part where my experience comes into play: the pregnancy check.
Walking with
Just like the ultrasounds used on humans, we use a mobile ultrasound machine to find out if there is a shark eye. I put on a pair of goggles that allow me to see everything the ultrasound can see, lean over the side of the boat, and place the probe on the shark’s belly upside down. The image is usually blurry at first as water splashes over the shark and up onto the boat. The team holds the shark still while I slowly move the probe along its belly. Then, if she is pregnant, something magical happens.
Baby tiger sharks, up to 40 of them tightly packed together inside their mother’s womb, are visible before my eyes. The image can also be seen on a screen held by another crew member on the boat, with everyone laughing as they gather around to watch the secret life of the unborn shark. We watch them as they pump fluid through their still-developing gills, and we watch as they scurry about, unaware that anything unusual is happening outside in the world. Once we have enough data on the approximate size of the offspring – which gives us an idea of how long the pregnancy is – it’s time to tag the mama shark.
Holding the probe as still as possible to keep the shark’s internal anatomy visible, Dr. Sulikowski takes the Birth Tag and uses a custom-made applicator to carefully insert it into the uterus through the urogenital opening. No surgery required, the tagging procedure is completed in a few minutes. Once the tag is inside the uterus, we rotate the shark upright to wake it up and release it back into the open ocean. I am filled with hope as I watch her gracefully swim away to continue her pregnancy, with a stow-away Birth Tag hidden among her unborn offspring.
Solving the mystery
Last December, we deployed the first Birth Tags on three pregnant tiger sharks. For tiger sharks, pregnancy is estimated to last 12-16 months, but researchers don’t have much hard data. Since these tagged sharks ranged from recent mating to mid-gestation, an added benefit of this study is that it may help refine estimates of pregnancy length for this species.
Although we work in the Bahamas, a shark sanctuary where it is illegal to kill sharks, tiger sharks migrate widely. Therefore, each tagged shark will likely spend time outside the Bahamas in unprotected waters where it will have to navigate carefully to avoid interaction with fishing gear. Tiger sharks are considered near threatened by the International Union for Conservation of Nature and their populations are currently in decline. The data we get from this first round of tags will provide us and policy makers with information that could inform future protections for this species.
We are currently waiting for a notification from our online ARGOS satellite system to alert us that one of our sharks has been born. When that happens, we will be the first in the world to know, close to real time, where and when tiger sharks live.
Many shark species are threatened with extinction, and understanding their reproductive cycles is critical to the effective conservation of these beautiful, ecologically important creatures. Using the Birthtag, we are about to unlock this information about tiger sharks and we hope this can be done for many other species.
We are planning future trips to use many more Birth Tags, but for now, we will have to keep singing the “Baby Shark” song as we patiently await our first glimpse of the private lives of these incredible creatures.
This story has been updated to remove a photo of the Birth Tag.
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This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. It was written by: Hannah Verkamp, Arizona State University
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Hannah Verkamp works for Arizona State University as a Research Associate in the Sulikowski Shark and Fish Conservation Laboratory. The research is funded by the Herbert W. Hoover Foundation.
