Reproductive regionalization was observed among in situ females with the majority (83%) of North Carolina females in an active state of reproduction and all Delaware females in a resting reproductive state. Nineteen aquarium females from five aquaria were examined longitudinally for two or more consecutive years. In situ sharks were sampled from Delaware Bay (n = 29), North Carolina (n = 39) and South Carolina (n = 11) during April-November from 2015–2020. The reproductive cycle was divided into eight stages based on ovarian activity and uterine contents. Reproductive status of in situ and aquarium female sharks was assessed using ultrasonography and plasma hormone (17β-estradiol, testosterone, and progesterone) monitoring. Additionally, comparison of reproductive observations from successfully reproducing in situ sharks and aquarium sharks may help elucidate reasons for lack of reproduction among aquarium sharks and aid the development of assisted reproductive techniques for managed populations. Animals in managed care, such as aquariums, provide the unique opportunity for longitudinal study in contrast to in situ sharks that are examined opportunistically, and at a single point in time. Fundamental characteristics of the reproductive biology of female sand tiger sharks Carcharias taurus are needed to understand the periodicity, seasonality and environmental factors essential for reproduction in this iconic species.
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