During July’s annual “Shark Week”, Olympic champion swimmer Michael Phelps went head to head with a Great White shark in a 100 meter race. Fortunately for Phelps the shark was not real, but instead a computer simulated fish created using data on the swimming speed of sharks. Despite being equipped with a wetsuit and a monofin that mimicked a shark’s powerful tail, Phelps swam the race two seconds slower than the shark. Just what exactly makes great white sharks such speedy swimmers?
Whilst Phelps can reach impressive speeds of 6 mph, great white sharks can swim up to 25 mph, potentially 35 mph in small bursts. This makes them the third fastest swimming shark in the world – beaten only by Salmon sharks and Mako sharks, which can swim up to 50mph and 60mph respectively. Explanations for this speed include warm blood temperature, enormous size and a high metabolism, as we will discover.
Firstly, great whites are thought to have a slightly warmer blood temperature than other shark species. Whilst most sharks are cold-blooded, great whites and other species of sharks belonging in the family Lamnidae, for example Mako sharks, are partially warm-blooded. They can be characterized as endotherms, meaning they are capable of generating heat internally. Their ability to do this stems from their special blood vessel alignment, specifically known as rete mirabile. This is a network of capillaries where the heat produced from muscle activity is recycled into colder blood through counter-current exchange.
More specifically, the vessels are arranged in such way that the warm blood coming from the swimming muscles is aligned to the cold blood coming from the gills, meaning heat can be easily transferred. The arteries in the rete mirabile carry oxygenated blood from the gills that have been in close contact with the outside water, decreasing the blood’s temperature. These meet a bundle of veins that are carrying heated de-oxygenated from the organs, and the heat is passed from these veins to the colder arteries. Great whites have these systems in their swimming muscles, brain and stomach, allowing them to increase the temperature of organs in these areas to around 14 degrees above the surrounding water. Therefore, they can inhabit waters that are too cold for other sharks. As blood on the way to be delivered to the swimming muscles is pre-warmed, this keeps their muscles readily powered. As we all know, a warm muscle is better than a cold one when it comes to activity, meaning sharks can swim at high speeds for long periods of time.
Another adaptation for speed held by great whites is their enormous size, which gives them great power. Great whites exhibit significant differences between genders, and the females are significantly larger than the males. On average, males weigh around 522 to 771 kg, with females being around 1950 kg. In fact, the largest individual weighed was an impressive 3,324 kg! Their gigantic size means they have extremely strong tail muscles which they use to power them through water at great speeds. Complementing their size is an extremely streamlined body. The torpedo like shape minimizes drag, whilst their pectoral and dorsal fins mean they can glide seamlessly through the water.
Finally, the great white shark has a high metabolism. Their blood has high levels of hemoglobin, meaning at any given time there is a high amount of oxygen being pumped around the shark. This allows plenty of aerobic metabolism to take place. On top of this, the ventricle of the great white – which is where oxygenated blood is pumped out of the heart to the rest of the body – is well muscled. This allows for lots of oxygenated blood to be pumped around the body at a fast rate. Together, these adaptations mean that oxygen is readily accessible at all times in a great white, allowing for plenty of aerobic respiration and thus a constant, immediate supply of energy. It is this energy that enables great whites to become such speedy swimmers.