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It's Shark Week!
It’s Shark Week on the Discovery Channel and the perfect time to highlight one of our sharks on display at the Aquarium…the swell shark.
Swell sharks are adapted for blending in on the ocean floor with alternating patches of tan and brown offset by dark brown and small white spots. Since the swell shark is nocturnal, this coloring provides excellent camouflage during the day when swell sharks maintain a low profile lying in caves and rock crevices typically in water less than 75 feet deep.
At night, swell sharks are active and hunt for fish close to the ocean floor and catch food using two different techniques. They will either slurp their food by sucking fish in quickly or use what is called the yawn, which entails patiently waiting with their mouth gaping open until a fish swims in or is swept in by the currents. These eating strategies work well for swell sharks allowing them to grow up to 43 inches in length.
To avoid becoming dinner themselves, swell sharks have a very cool adaptation. When they feel threatened, swell sharks grab their tail by the mouth and form a “U” shape, then they inflate their stomachs by swallowing water or air and swell their bodies up to double the size like a big balloon, hence their common name swell shark. Once danger has passed, the swell shark spits out the water or air and its body returns to normal size.
Taking a passive approach to defense is the same approach swell sharks use in their reproductive strategy. Instead of actively guarding the eggs, female swell sharks lay two to four eggs at a time and leave them laying on the ocean floor. Each egg contains a yolk that provides all the nutrition a developing embryo needs to grow, similar to a bird’s egg.
The eggs are brown, slightly translucent and shaped like a purse. This is why we call empty eggs washed up on the beach mermaid purses. On the ends of each egg are long adhesive tendrils that catch on rocks or seaweed that prevent eggs from washing away. When a young shark is ready to hatch it uses tough scales on its back to break open the egg case and start life in the open ocean without any help from its parents.
Stop by and visit our swell sharks during your next visit. Tank 15 features baby swell sharks, plus a close up look at swell shark eggs in six different stages of development. In tank 35, you can see our adult swell sharks resting during the day to support their nocturnal lifestyle.
Post Date: Saturday, August 11, 2012
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