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How Pygmy Sharks Work

A spined pygmy shark, or a creepy finger puppet? See more pictures of sharks.
Norbert Wu/Getty Images

In the deep waters of the Earth's oceans, size matters. Just ask the great white shark. At 20 or more feet long, it ranks as one of the largest predators in the ocean and you'd have a hard time finding a more feared fish. Bull and tiger sharks are no slouches either, growing to lengths of 10 to 15 feet, with healthy appetites. The advantage that size offers in the ocean is that the larger you are, the fewer fish there are that will have the desire and ability to try to eat you -- most fish feed on prey smaller than they are. The bull shark is an exception -- it often goes after larger prey. But the bull shark aside, chances are if you're the big fish, you'll be safe from predators.

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The size of your standard common shark, or elasmobranch, ranges from the four-foot-long spiny dogfish shark to the 40-foot whale shark -- and there are a lot of sizes in between. At the other end of the spectrum, there's the spined pygmy shark, squaliolus laticaudus. The poor pygmy is just a little guy. They only grow to about 9 inches long (25 cm), and that's about the biggest one you'll ever find. The pygmy's average size is only 7 to 8 inches (17 to 20 cm). Not much is known about its weight, but at that length it can't be much.

Yo­u'd think th­at being so small would make the spined pygmy shark an endangered species. Instead, it's actually one of the few sharks that isn't threatened. The pygmy may be small, but it has a couple of tricks up its sleeve to help it avoid the jaws of larger predators. Even though the pygmy is thought to be abundant, it's rarely seen by humans because of the depths it lives in. This trait has left the pygmy as somewhat of a mystery in the shark world. And since it doesn't pose a danger to humans and it isn't fished for its tiny little fillet, researchers haven't put a lot of time into studying it.

In this article, we'll tell you what we know about this diminutive shark -- where it swims, what it eats and what it does to avoid the jaws of its larger cousins.

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Illustrated side view of Pygmy Shark -- Squaliosus laticaudus
Illustrated side view of Pygmy Shark -- Squaliosus laticaudus
Dorling Kindersley/Getty Images

At its size, you'd think the spined pygmy would be the smallest shark. Researchers believed it was, until the discovery of the dwarf lantern shark. This little fella is an inch shorter than the pygmy. Like the dwarf, the pygmy is a deepwater fish. It's not because they have a preference for cooler waters -- it's a survival tool. The deeper you go into the ocean, the less likely you are to find larger predators.

You might also think that being small would have disadvantages come dinner time, but there's always something smaller to eat in the ocean. Pygmy sharks are actually pretty fierce predators for their size. If you're a shrimp, small squid or lantern fish, you'd better watch your back -- there may be a pygmy shark on your trail. Pygmies stay in depths of about 6,500 feet (2,000 meters) by day, but migrate vertically at night to hunt in depths of about 650 feet (200 meters.)

Pygmies don't look like other sharks, but they don't look exactly unlike sharks either. Imagine a shark drawn on your index finger and you'll be close. It's slender, grey to black with lighter colored fins and its mouth lies under its pug nose, like most sharks. Its lower teeth are larger and more heavily serrated than its smooth uppers and like other sharks, it replaces its teeth as needed. Not much is known about the life cycle or reproductive practices of the pygmy shark, but we do know that it lays eggs that hatch after birth, while many other sharks birth live pups.

The "spined" feature of the pygmy is one thing that sets it apart from its relatives. The pygmy is the only shark that has a pointy spine in the front of its first dorsal fin, but not the second. Not exactly something to brag about, but there's another physical trait the pygmy shark has that might make other sharks a little jealous -- it has a bioluminescent belly. This means that it glows in the dark. There are all kinds of sea creatures that have this unique feature, but the pygmy is the only glowing shark.

There are a couple of theories as to how the pygmy uses its glowing belly, and neither one has to do with lava lamps and incense. It's most likely an attractant to smaller prey that swims underneath it. The smaller fish approach the glow and before you know it, the dinner bell rings. Another perk to a glowing belly is that it may provide camouflage from predators. From below, the glow blends into the light from the surface above, making it less visible to predators. You can read more about this fishy feature in How Bioluminescence Works.

For more information on sharks and related topics, swim over to the links on the next page.

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Sources

  • "Pygmy Sharks." Shark Foundation, 2008. http://www.shark.ch/Database/Search/species.html?sh_id=1114
  • "Pygmy Sharks." sheppardsoftware.com, 2008. http://www.sheppardsoftware.com/content/animals/animals/fish/shark_pygmyshark.htm
  • "Spined Pigmy Shark." discoverychannel.co.uk, 2008. http://www.discoverychannel.co.uk/sharks/detail/pygmy/index.shtml
  • "Spined Pygmy Shark." nmh.org, 2008. http://www.nhm.org/research/fishes/sharksff/sharkimg/sff5.html
  • "Spined Pygmy Shark." sharks.findouthow.org, 2008. http://sharks.findoutnow.org/article-13-spined-pygmy-shark.html
  • Swaminathan, Nikhil. "Not So Tall Tale: Why Pygmies Evolved to Be Shorter." Scientific American. Dec. 12, 2007. http://www.sciam.com/article.cfm?id=why-pygmies-evolved-to-be-shorter

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