Wild, free-swimming whale sharks in the Galapagos successfully ultrasounded and blood-sampled to observe their reproductive states – the first time these techniques have been applied in the wild!
Q & A
What are some of the challenges presented by doing underwater ultrasounds? How did the team overcome them?
These techniques were quite challenging to apply. First, we’re working at 10–30 m beneath the surface, often in strong currents. Second, whale sharks are wonderfully placid, but they’re a lot faster than us, and emerge from the blue with little warning; we only get a short time to work with each animal. The ultrasound unit is the size of a large briefcase, so it’s far from hydrodynamic. Rui, the lead author of the study, was using a ‘jetpack’ (actually an underwater propeller mounted on his air tank) to keep up with the sharks and scan them with the ultrasound wand. I felt cool by general association.
Interpretation of the scans requires a lot of experience, too. Rui was filming the process with a GoPro so that we could synchronize the ultrasound imagery with the position on the shark. Kiyomi Murakumo has been examining underwater ultrasound imagery in captive sharks and rays in the Okinawa Churaumi Aquarium for years now, monitoring pregnancy in species from nurse sharks to manta rays, and she was able to discern the developing eggs in these greyscale images that prove that these female whale sharks are indeed adults – something that was previously only possible through dissections.
Collecting blood samples from free-swimming sharks is, similarly, something that has taken a lot of trial and error to get right. Whale sharks have extremely thick skin, so we can’t reach their actual veins – instead, we’re trying to draw blood from vascularised tissue on their fins. That generally only works on relaxed sharks, and requires a large dose of luck! We also have to avoid contamination from seawater, which has necessitated the development of a two-syringe system, with one creating an initial vacuum, enabling the second to draw pure blood.
• Why do we know so little about whale shark reproduction when they are kept in captivity for a while now and are considered an ‘iconic' shark species?
Whale sharks are a relatively well-studied shark, but ‘relative’ is still a key word here. Only one pregnant female, caught in a Taiwanese fishery way back in 1995, has ever been examined by scientists – and we don’t know where the babies live, either. It’s mostly juvenile male sharks that frequent coastal areas and tourism sites. Females, both juveniles and adults, probably live offshore, where they’re difficult to find, let alone study.
There are a few whale sharks in some large aquaria, such as the Okinawa Churaumi Aquarium and Georgia Aquarium, but no adult females. The Okinawa aquarium has a very sexually frustrated adult male whale shark, which matured in their facility, but females probably don’t become adults until they’re over 30 years old, so it might have to continue waiting for a while yet.
• Why did the team choose the Galapagos to do this research over other whale shark hot spots?
Darwin Island in the Galapagos, where this research was conducted, is one of the only places where adult female whale sharks are consistently seen. Between June and October each year there’s a good chance to see them swimming by. The Galapagos Whale Shark Project team have huge expertise in this area, so it was a great opportunity to test and refine these new techniques.
• How does this technological technique help scientists understand the physiology of whale sharks – and can it help other vulnerable shark species?
Shark biology studies used to be based on dissections. For endangered species like the whale shark, where we’re doing everything possible to keep them alive, that’s made us quite creative in the development and application of new techniques, such as underwater ultrasound and in-water blood sampling. Now, we can start investigating their reproduction while they’re in the wild – and it’ll allow for other studies too, such as looking at stress or pollution levels in their populations, which really improves our understanding of their conservation needs.
Whale sharks are gentle giants, so they’re lovely animals to work with, and have become a bit of a ‘poster species’ for the use of new techniques, like photo-identification and laser photogrammetry, that are then adapted for other endangered sharks and rays. Other groups are already starting to use underwater ultrasound wands on poles to scan tiger sharks while they swim by. It’s going to unlock a lot of new opportunities for minimally-invasive research, that can give us a wealth of information while avoiding any harm to the animals. It’s been a super exciting project to be part of!
Q & A by Don Silcock