By employing the same kind of ultrasound imaging technology used on pregnant women, scientists from the University of New England and University of Miami have found a less invasive way to study the reproductive biology of female tiger sharks.
Compared to previous methods involving the dissection of presumably pregnant sharks, which ultimately kills the animals, researchers have preformed in-water ultrasounds on live tiger sharks ("Galeocerdo cuvier") at Tiger Beach in the Bahamas - a site known for its year-round abundance of tiger sharks.
Ultrasound technology gives researchers the opportunity to survey the animal's abdomen and look for the presence of embryos in female sharks. They also took blood samples for hormone analyses to further investigate the reproductive status or maturity of females.
"Using the same ultrasound imaging technology used on pregnant women, we discovered Tiger Beach was important for females of different life stages, and that a high proportion of tiger sharks were pregnant during winter months," said James Sulikowski, a professor at the University of New England's Department of Marine Science, in a news release.
Marine predators such as sharks have faced drastic population declines, as the fishing of pregnant females has a significant impact on the health and viability of both local and regional populations.
For instance, female tiger sharks give birth to between 10 and 80 pups at a time. The gestation period usually lasts for 14 months on average; however, pups can remain inside their mother for up to 16 months. Adult females are generally ready to start mating when they are about 8 years old. Therefore, populations can be greatly impacted if a pregnant female were to be killed, and no babies were born to ensure the survival of the subsequent generation.
"Our data suggests that Tiger Beach may function as a refuge habitat for females to reach maturity as well as a gestation ground where pregnant females benefit from calm, warm waters year-round that help incubate the developing embryos and speed up gestation," added study co-author Neil Hammerschlag, a research assistant professor at the University of Miami Rosenstiel School and Abess Center for Ecosystem Science and Policy.
Tiger Beach is located within the Bahamas Exclusive Economic Zone, where shark fishing has been banned since 2011. Therefore, researchers suggest the relatively high shark populations seen in the Bahamas sanctuary, compared to other parts of the Caribbean, may in part be due to the increased protection of mature and gravid females.
"It is crucial for marine biologists to understand their behaviors to provide information for resource managers to effectively protect and manage them," said Hammerschlag.
Their study was recently published in the Journal of Aquatic Biology.
