Momma
Shark
In a pioneering collaborative effort between Fuvahmulah Dive School, Pelagic Divers Fuvahmulah, the Suliwoski Lab, Oregon State University, and Miyaru, we were conducting the first dedicated ultrasound study on free-swimming tiger sharks in Fuvahmulah. Using specialized underwater ultrasound equipment, the team can non-invasively assess reproductive status, detecting pregnancies, ovarian development, and overall health. This project represents a major leap in shark science, offering unprecedented insight into the breeding biology of tiger sharks in one of the world’s most important shark hotspots.
We used a high-definition submersible ultrasound at Tiger Harbor, Fuvahmulah, to assess the reproductive state of free-swimming tiger sharks.
We observed 69 female sharks (44 adults, 25 subadults), 36 swam close enough to be scanned, 32 of those were identified as adults, and the transducer made contact long enough to obtain usable scans on 28 adult sharks. Of those 28 adults, 26 (93%) were gravid, embryos were visible on ultrasound.
Embryos across the gravid sharks sorted into two distinct size cohorts: the first group (n = 19) had a mean embryo length of approximately 8.2 cm, and the second cohort (n = 7) exhibited a mean length of approximately 18.4 cm. The authors note that this bimodal distribution in embryo size may indicate asynchronous reproductive cycles within the population or reflect differences in exposure or habitat histories among the females.
Ultrasound analysis in tiger sharks works very similarly to how it is used in other large animals, but it is adapted for use underwater and on free-swimming sharks.
A portable, waterproof ultrasound unit is placed gently against the shark’s abdomen while the animal is calmly guided alongside the boat or held in a controlled in-water position by trained safety divers.
The probe sends high-frequency sound waves into the body; when these waves reflect off internal tissues, the returning echoes create real-time images on the screen.
In our ultrasound study, Embryos were visible on the scans as clearly defined structures inside the uterus. Because embryonic tissues and surrounding uterine fluid reflect sound differently, the embryos appeared as distinct shapes with measurable body outlines.
In many of the gravid females, individual embryos could be identified by their vertebral columns, body curvature, and the bright (hyperechoic) margins typical of developing shark pups. These visual markers allowed researchers to confirm pregnancy, count developing embryos, and place them into size cohorts, providing unprecedented insight into tiger shark reproduction without harming or restraining the animals.
Figure 3. (A–C) Representative transverse ultrasound images of tiger shark Galeocerdo cuvier embryos measured using E.I Medical Imaging proprietary software. Embryo’s separated into two discreet groups (students t test, p-value < 0.01); (A)group one (n=19) measured 8.2 cm (0.5 cm) in total length (TL) and (B) group two (n= 7) measured 18.4 cm (1.4 cm) in total length (TL). (C) represents the scan from a non pregnant tiger shark. Arrow points to uterus.
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