Measuring the swimming speed of the ocean’s slowest shark

BBC : Something has been killing harbor seals in Svalbard, a remote Arctic archipelago. Among the prime suspects was the Greenland shark, but the few-meter-long fish were thought too slow to catch the nimble mammals. A new study , published in the Journal of Experimental Marine Biology and Ecology, confirms that the sharks can’t match the seals in speed, even for short bursts. By attaching sensors to the sharks’ bodies and tail fins, Yuuki Watanabe of Japan’s National Institute of Polar Research and his colleagues determined that the sharks take 7 seconds to complete one full wag of their tails and can sprint at a maximum speed of 0.7 m/s, which is significantly slower than the seals’ mean speed of 1.0 m/s. It turns out, though, that the sharks do catch and eat sealsâmdash;by sneaking up on them when they sleep in the water to evade polar bears.