A Sharks Tale Recorded on PowerLab
 Grasping a live shark in your hand whilst it uses its defensive electric charge isn’t part of a typical day in the laboratory for most scientists. However, it is necessary for the Shark Lab’s Laura Macesic, as she investigates whether the lesser electric ray uses its charges (produced by two sets of specialized muscle cells) not just to defend itself, but also to communicate with other rays. Whilst this ray isn’t really the most threatening shark species around - its defence mechanism is an average 35 Volt charge which is enough to shock, but not injure an adult human - Laura has developed an insulated rubber glove embedded with electrodes in the fingers and thumbs so she can grasp the ray as it emits its charge. The electrodes forward the charge signals into a differential amplifier and then the PowerLab, which records and analyzes the charges’ voltage and frequency. Predictably, Laura’s discovered that the bigger the ray, the bigger its charge’s voltage. However, she’s also discovered that the electric ray is capable of producing a 60 Volt charge, almost double the species’ generally accepted maximum charge, with a peak discharge frequency of around 200Hz - scuba divers beware. |
 Another scientist at the Shark Lab, Mikki McComb, uses a research technique that’s actually fairly common amongst PowerLab users- the electroretinogram. However, whilst most researchers are investigating the eyesight of mice and rabbits, Mikki is working with Atlantic stingrays, clearnose skates and lemon sharks, with future plans to investigate a variety of hammerhead species. In order to quantify the animal’s visual fields, she connects glass microelectrodes to the shark’s retina. When the shark is exposed to light, the retina produces electricity, and this signal is sent to the PowerLab. How much the shark can see is determined by comparing the amount of electricity produced with how much light the shark was exposed to. Mikki’s discovered that even distantly related shark species share similar visual fields, and that even though their eyes are positioned on two different facial planes, they still have overlap between their left and right fields of vision, meaning most sharks can see you really clearly in the water! |
 Sharks, as we all know, smell blood in the water. Rather than just being scared of this fact, Tricia Meredith’s decided to explore it, and investigate exactly how well a shark can smell. Tricia uses a technique known as an electro-olfactogram, where chlorided silver wire electrodes detect the negative charge produced when an odorant binds to part of the olfactory (or smelling) system of a shark. The PowerLab then acquires and analyses this information. Tricia is discovering that bigger sharks aren’t necessarily better smellers, and the shark’s ability to smell in the water is actually pretty standard for a fish. It’s just that sharks do really care when they smell blood in the water! |
31 July 2006
