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

• Published in: Endangered Species Research
• Main Authors: R Matsumoto, K Murakumo, R Nozu, D Acuña-Marrero, JR Green, SJ Pierce, CA Rohner, H Reyes, SM Green, ADM Dove, ML Torres, AR Hearn
• Format: Article in Journal/Newspaper
• Language: English
• Published: Inter-Research 2023
• Subjects: Zoology; QL1-991; Botany; QK1-989; Darwin Island; Galapagos
• Online Access: https://doi.org/10.3354/esr01226; https://doaj.org/article/6eac6b8d9290458592e7b6338c94a0a8

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.