University of North Florida researchers are taking an innovative approach to shark conservation: Rather than following the normal course and dissecting presumably pregnant specimens to get a better idea of population variables, Dr. James Gelsleichter and his team are using the same kind of ultrasound imaging technology used on pregnant humans.

"Our hope is to develop an indicator of pregnancy in sharks, so we take blood and ultrasounds to determine if a shark is pregnant or not," Dr. Gelsleichter, an associate professor of biology at the University of North Florida (UNF), told Nature World News.

With a better understanding of shark reproduction – specifically of those that suffer from intense fishing – researchers can better estimate population growth rate, and, in turn, conservation status.

"If you know how many animals are out there, you can estimate at what point they mature and how often the reproduce, and how many offspring they are going to have," Dr. Gelsleichter, who is also the director of UNF's Shark Program, explained. "We are kind of creating a 'budget' for how fast the population grows."

With this "budget" researchers can determine how many sharks fisheries are permitted to be removed from the general population without putting the species in "the red" – or at risk of extinction.

For their study, researchers focused on a few coastal sharks that inhabit northeast Florida waters and are fished commercially. This includes the bonnethead or shovelhead shark, the smallest hammerhead species; the Atlantic sharpnose shark, the most common in the area; the Oceanic whitetip shark, which is commonly associated with attacks and globally threatened; the blacknose shark, a relatively small species characterized by a black blotch on the tip of its snout; the finetooth shark, a species highly valued for its meat; and the smalltooth sawfish, an endangered ray species that resides only in South Florida.

In the case of the smalltooth sawfish, ultrasound is particularly important to check how quickly they are rebounding. The animals were placed on the Endangered Species List in 2003, after being brought to near extinction by fishing practices such as trawl and inshore netting. Smalltooth sawfish are characterized as "critically endangered" on the International Union for Conservation of Nature's (IUCN) Red List of Threatened Species.

Ultrasound helps researchers answer four primary questions: What age do the animals become sexually mature? How often do they reproduce? When does reproduction occur? And how many offspring do the animals have in a given year?

To perform the ultrasound, sharks are captured and tethered to the side of boats. While remaining in the water, the sharks are inverted so that their abdomens face upward. To keep the sharks calm, researchers orient the boat into the current so that water can flow over their gills.

Larger sharks are they exception when it comes to ultrasounded. They still have to be lifted out of the water and onto the boat.

Dr. Gelsleichter and his team use a semi-rugged, water-resistant portable ultrasound machine commonly used by veterinarians and manufactured by E.I. Medical Imaging. To counter the glare of sunlight bouncing off the water, researchers wear goggles that feed into the ultrasound. Sounding gel is placed on the probe, which is then covered in plastic to protect it from being washed off and from the sharks' rough skin.

When performing ultrasound on a shark this is the type of bouncing baby image that you might see:

"What we'll do is scan it almost at a cross-sectional view of its ventral side [Belly]," Dr. Gelsleichter explained. "Then what you'll see looks like a 'tear drop' or a 'water drop.' At the top portion of that you'll see little finlets and the fins themselves; you'll see the muscle bundles, the vertebra – which is made of cartilage, and then you'll see an area that is kind of cloudy, where all the internal organs are. All calcified, or hard, areas are very white."

The idea is that you can count the number of these "tear drops" to see how many babies, or "pups," the pregnant shark is carrying.

Researchers have also studied characteristics of shark reproduction by identifying certain hormones – estrogen and testosterone – in the blood, which allows them to identify different reproductive stages. For instance, estrogen levels are higher when females are producing eggs, and high levels of testosterone indicate males are producing sperm. In other words, this is a good indication that the animals are preparing for mating season. The hope, researchers say, is to identify a specific blood marker for pregnancy.

Every method has its limits, though. Ultrasound, for example, is not all that reliable during the early stages of pregnancy because the embryos' vertebra has not calcified enough to be detected. This accounts for many "false negatives." Alternatively, blood indicators may be useful for "early pregnancy tests," but they don't indicate the number of babies a female is carrying.

Most sharks are seasonal or annual reproducers (every other year vs. every year). Since it is different for every species, ultrasound helps identify how often reproduction occurs. For instance, if all sharks of one species appear to be pregnant when surveyed, it is a good indicator they are annual reproducers. On the other hand, if only 50 percent of the animals caught and ultrasounded appear pregnant, it indicates the species gives birth every other year, essentially cutting their population in half, Dr. Gelsleichter explained.

The end goal is conservation. Dr. Gelsleichter said: "We need concrete data, we need hard numbers in order to figure out how fast a population grows so that it can be matched properly. The idea is to use a number of different approaches, like blood hormones and ultrasound, to estimate population growth and recovery."

Here is how you would conduct ultrasound on a shark:

Related Articles 

Shark 'Tank': Blacktips Gather In Huge Group Near Coast

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).

-Follow Samantha on Twitter @Sam_Ashley13