FEATURES
TOP: Kiyomi Marakumo taking a whale shark’s blood sample. BOTTOM ROW: Photos by Jonathan R. Green. 1. The Research Team. 2. A different method was used to attach a satellite tag by clamping it to the tip of the dorsal fin. Close-ups of the tags. (www.galapagoswhaleshark.org/)
results were promising. “We confirmed the presence of follicles in the ovaries but none of the images captured embryos or egg capsules inside the uterus. These adult female sharks we saw at Darwin Island might be on their way to mate fur ther offshore. I am confident that we can judge the sexual maturity, and probably also determine the pregnancy of whale sharks in the field, using the underwater ultrasound”. The researchers attached satellite-linked tags to the sharks to track their onwards movements. Professor Alex Hearn from the University of San Francisco/Galapagos Science Center explains, “We’ve tagged whale sharks in Galapagos before, but there are lots of predatory sharks at Darwin and they often try to eat the tags, which can rip them out of the whale sharks almost immediately. To reduce early tag loss, we tried a different method on this trip, clamping the tags to the tip of the dorsal fins. All tags are transmitting well, so we
should get great information on where these sharks swim over the months to come.” Project member Dr. Alistair Dove, from Georgia Aquarium, notes that these tags could document some amazing behaviours: “Whale sharks are already known to be the deepestdiving of all fish. The current depth record is 1,928 m – well over a mile – set by a juvenile whale shark. Larger, older animals can generally dive deeper than young smaller ones, so perhaps we will challenge that record.” Kiyomi Murakumo, from Okinawa Churashima Foundation, successfully collected blood samples from six adult sharks – no easy job. Her colleague, Dr. Ryo Nozu, analysed the results immediately following the trip: “Sex steroid hormone levels in the blood are an excellent way to monitor reproduction in individual sharks. This study measured levels of estradiol, progesterone and testosterone of wild, adult female whale sharks for the first
time in the world. Estradiol could be associated with follicular development, and progesterone could be involved in ovulation and pregnancy. Over time, as we sample more whale sharks, we can build up a complete picture of their reproductive cycle by combining the blood sampling with the ultrasonography.” Jonathan R. Green added, “These big female sharks are not going to give up their secrets easily. One thing is clear, there’s a lot of work still to do to understand the reproductive processes of this endangered species. However, this trip proved that it is possible to research their breeding in the wild. We’ll continue to hone our techniques and build upon this knowledge, as we need to understand these enigmatic sharks and protect them through their life cycle.” This project was supported by Galapagos Conservation Trust, Planeterra Foundation and Temperatio. DECEMBER 2018 | DIVERS FOR THE ENVIRONMENT
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