A hammerhead shark from the Natural History Museum is helping scientists to investigate how sharks smell their prey.
A drop of blood a kilometre away is no problem for a shark’s sense of smell and this skill could prove useful to scientists in other areas where detecting chemicals is important, such as underwater exploration, environmental pollution such as gas leaks from underwater pipelines, or even counter terrorism.
Sharks smell when they swim forward and propel water through the tiny channels inside their nose. Museum scientists and those from the University of Bath and University of Cambridge are studying how this water flows.
Dr Jonathan Cox of the University of Bath who led the research explains. ‘The nasal cavity of the hammerhead is like a labyrinth of pipes, with a central U-shaped channel and lots of smaller channels leading off it.
Shark model is placed into the flow tank © Nic Delves-Broughton /University of Bath
'The smaller channels contain the olfactory receptors, and so we’re looking at how the water flows through these channels as the shark swims forwards.’
To study the water flow, the team made an accurate 3D model of the head of a 50-year-old hammerhead shark specimen from the Museum's collections. They did this by putting the specimen through a CT (Computed Tomography) scanner.
The resulting digital images are then converted, layer by layer, into a 3D object. This is known as 3D printing. The resulting model, including its internal cavities, is accurate to 200 micrometres (1 micrometre is 1/1000th of a millimetre).
Dyed water flows through the shark model © Nic Delves-Broughton /University of Bath
The shark head model was then placed in a tank of flowing water to monitor how the water flows through the nasal cavity channels. The angle of the head was also changed to reflect how the shark turns its head from side to side as it swims. This is the first time shark sense of smell has been studied in this way.
'This is an excellent piece of research,' says Dr Richard Abel, Museum Micro Tomography Specialist who scanned the shark. 'The project utilised a very old Museum specimen to answer fundamental and wide-reaching questions by applying cutting edge technology and expertise.'
Museum's hammerhead shark head specimen, showing its mouth, used in the shark smell research.
Dr Abel scanned the shark in the CT scanner at the Museum. It is usually kept preserved in liquid in a jar and scanning it wasn't an easy task, as Dr Abel explains.
'It was very difficult to scan the hammerhead because the specimen was delicate, awkwardly shaped and had to be kept wet throughout.'
'I wrapped the specimen in plastic to stop it drying out. Then I very gently mounted the head in Oasis floral foam (the green foam florists use to arrange flowers). All very high tech!'
The shark species used in this research was a smalleye hammerhead, Sphyrna tudes. Worldwide, there are 8 hammerhead shark species, the largest being the great hammerhead, with reports of an animal that grew to just over 6m.
Hammerhead sharks are fish. However, they do not lay eggs but instead, give birth to live young, a process known as viviparity. They belong to the genera Sphyrna and Eusphyra ('sphyrna' is Greek for hammer) and their bizarre hammer-shaped head is thought to help them sense electrical signals, which they use to detect prey. Rays are a favourite food, but they also feed on fish, crabs, squid, lobsters and other sea creatures.
This research combined the expertise of scientists, CT scanners and fluid mechanics as Dr Cox concludes, 'The nice thing about this project is its interdisciplinary-ness. Museum curators, CT specialists and engineers all had a hand in its success. Without them the project would have fallen flat on its face.'
The research is published the scientific journal Comparative Biochemistry and Physiology Part A, volume155, pages 464-475, 2010.
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