Mothers have long demonstrated the maternal instinct, that undeniable urge to care for their offspring. Science has just recently determined that it has a biological basis. A 2008 study of mothers who were shown video footage of children crying and smiling reacted differently than when video of their own child crying or smiling was displayed. In magnetic resonance imaging (MRI) scans, neurons in the mothers' brains lit up when they saw their child, especially in the case of seeing their child cry [source: The New York Times].
So we could argue that mothers are wired to respond to their children. But humans aren't the only animals who display this caretaking imperative. Evidence of this instinct is found in almost every species on Earth. And it isn't strictly relegated to caring for offspring or members of the same species. In one instance in 2008, a King Charles spaniel named Ellie made news after she took it upon herself to care for a litter of rabbits whose mother had died [source: National Geographic].
You can certainly understand where Ellie the spaniel is coming from. You've adopted rabbits, too. Your sense of duty toward hurt and helpless animals hardly ends at the shoreline, though. You feel the same sense of responsibility to help hurt fish and other aquatic life. Say, there's a fish flapping about in the surf right now. Perhaps you should go see if you can help it. As you wade out to where the fish is struggling near the water's surface, a vague memory of an episode of "Mythbusters" you saw gnaws at you. Something about sharks and flapping fish... What was it? Oh yeah -- don't flapping fish attract sharks? While you stand there, waist-deep in the ocean and frozen in terror, you might as well turn to the next page to find out if it's true.
Injured and Struggling Fish: Steer Clear
That injured fish you found flapping around -- should you rescue it? Heck no! Instead, you should stay far away from injured and struggling fish. Their flapping has been shown to attract sharks. Just as land-bound predators like lions and tigers seek out the weakest of the group when they hunt for prey, so, too, do most sharks. And injured fish make about as easy prey as a shark's likely to find.
Fish don't have to be injured to attract sharks, either. Even just the flapping motion on the water's surface can draw a shark's attention. Fish that sharks prey on are also targeted by fishermen. When fishermen's nets capture masses of fish struggling to get free, it's like a neon buffet sign for sharks.
So how do injured and trapped fish attract sharks? They use a combination of their senses to detect potential prey. If a fish is injured and bleeding, a shark's legendary sense of smell comes into play. It's significant that sharks have noses since they don't use them to breathe (they have a gill system for that). Their noses are dedicated to detecting odors. Sharks have been shown to sense very small amounts of blood in the water -- as little as one part blood per million parts water [source: Shark Trust]. But fish don't necessarily have to be bleeding to be detected by sharks. The predators can also smell scents produced by fish in distress.
The senses of sight and hearing among shark species are also remarkable. Shark vision has evolved over the 400 million years the species has been around to get as much visual information as possible from the low light available underwater. And their hearing isn't too shabby, either. This is due, in part, to their aquatic habitat. Sound travels faster and farther underwater than it does through air, and sharks' hearing has adapted to pick up on minute sounds. Even recordings of the sound of flapping fish have been shown to draw sharks [source: Shark Trust].
What's more, sharks possess a sixth sense we humans don't -- they can pick up on electrical impulses, a sense called electroreception. Sharks have specialized organs called Ampullae of Lorenzini made of tiny hairs embedded in a jelly-like substance in pores on the underside of their heads. This system allows sharks to pick up on minute electrical impulses hundreds of feet away. Any organism with a nervous system generates electrical impulses to stimulate muscles and create motion. And electrical impulses are also created by motion itself -- such as the flapping of fish in water. Sharks use these electrical impulses to steer toward their prey, based on the weakness or strength of the signal [source: Davidson College].
But even with their highly developed senses working in conjunction to find prey, sharks can make mistakes. If you flap around in the ocean, you might look, sound and feel like a source of food to a shark. We all make mistakes -- even sharks.
For more information on sharks and other related material, visit the next page.
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More Great Links
- Parker-Pope, Tara. "Maternal instinct is wired into the brain." The New York Times. March 7, 2008. http://well.blogs.nytimes.com/2008/03/07/maternal-instinct-is-wired-into-the-brain/
- "Adorable dog adopts orphaned baby bunnies." National Geographic. http://jezebel.com/5011617/adorable-dog-adopts-orphaned-baby-bunnies
- "Electroreception." Davidson College. http://www.bio.davidson.edu/people/midorcas/animalphysiology/websites/2005/DiLuzio/electro-reception.htm
- "Island of the sharks: Exploding myths." PBS. June 2002. http://www.pbs.org/wgbh/nova/sharks/masters/myths.html
- "Senses of sharks." SharkTrust. www.sharktrust.org/do_download.asp?did=27360