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ESR 50:125-131 (2023)  -  DOI:

Underwater ultrasonography and blood sampling provide the first observations of reproductive biology in free-swimming whale sharks

Rui Matsumoto1,2,*,#, Kiyomi Murakumo1,#, Ryo Nozu3, David Acuña-Marrero4, Jonathan R. Green5, Simon J. Pierce6, Christoph A. Rohner6, Harry Reyes7, Sofia M. Green5, Alistair D. M. Dove8, Maria L. Torres9, Alex R. Hearn9,10

1Okinawa Churaumi Aquarium, Okinawa Churashima Foundation, Okinawa 9050206, Japan
2Okinawa Churashima Foundation Research Center, Okinawa Churashima Foundation, Okinawa, 9050206, Japan
3Faculty of Advanced Science and Technology, Kumamoto University, Kumamoto, 860-8555, Japan
4Institute of Natural and Mathematical Sciences, Massey University, Albany Campus, Auckland, 4442, New Zealand
5Galapagos Whale Shark Project, Cumbaya, 170901, Ecuador
6Marine Megafauna Foundation, West Palm Beach, FL 33411, USA
7Dirección Parque Nacional Galápagos, Galápagos, 200350, Ecuador
8Research and Conservation Department, Georgia Aquarium, Atlanta, GA 30313, USA
9Galapagos Science Center Dept. of Biological Sciences, Universidad San Francisco de Quito, Quito, 170157, Ecuador
10MigraMar, Forest Knolls, CA 94933, USA
*Corresponding author:
#These co-first authors contributed equally to this work

ABSTRACT: We report on a non-invasive technique for observing the reproductive states of wild, free-swimming whale sharks Rhincodon typus for the first time. Female whale sharks (n = 22) were assessed using underwater ultrasonography and a novel blood-sampling technique at Darwin Island in the Galapagos Marine Reserve, Ecuador. Despite the widely held assumption among researchers that the post-pelvic distention of large females is indicative of pregnancy, ultrasound provided no evidence of embryos or egg cases. However, the presence of follicles (diameter: 28.5-83.6 mm) was confirmed in 2 female sharks of 11-12 m total length (TL). Additionally, 3 steroid hormones (estradiol, testosterone, and progesterone) were analyzed in blood plasma from 6 female sharks (11-12 m TL). Hormone levels were similar to, or lower than, those obtained from an immature female in the Okinawa Churaumi Aquarium. Based on these results, we infer that female whale sharks (TL >11 m) in this study were mature but not pregnant. The techniques used here for whale sharks can be successfully used to obtain non-lethal field data on the biology and reproductive anatomy of this globally endangered fish, and are adaptable for use in other large marine species.

KEY WORDS: Elasmobranch · Conservation physiology · Maturity · Pregnancy · Hormone level · Galapagos · Rhincodon typus

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Cite this article as: Matsumoto R, Murakumo K, Nozu R, Acuña-Marrero D and others (2023) Underwater ultrasonography and blood sampling provide the first observations of reproductive biology in free-swimming whale sharks. Endang Species Res 50:125-131.

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