Sharks will eat anything.
Wrong. Sharks are pretty discriminate eaters. Even if we didn’t know this from examining the stomach contents of dissected sharks, it’s obvious from the wide array of adaptations found in different shark species. As I said in my shark diversity posts, each shark has evolved to fit a specific diet. Unless they’re injured or starving, there’s little motivation for a shark to waste energy pursuing something that isn’t their normal prey. Although tiger sharks have been nicknamed the “garbage cans of the sea” because a few odd things (license plates, shoes, glass bottles, ect…) have been found in their stomachs, these finds are actually quite rare.
Sharks will eat anything.
Without sharks, many of our favorite crustacean-based seafood dishes would drop off menus. Sharks, perfectly adapted to thrive as apex predators, maintain the ocean’s biodiversity by controlling the populations of marine species that are lower than them on food chains. As has been shown in Tasmania, Australia, removing sharks from an area has devastating effects on the ecosystems we depend on for seafood. Tasmania’s shark fisheries quickly exhausted local shark populations. With the sharks virtually gone, the squids dwelling in Tasmanian waters no longer had any predators. Their populations exploded and the rampant squids devoured all of the lobsters in the area until Tasmania’s lobster fishery collapsed. Other fisheries have suffered similar crashes from depleted shark populations, including those for scallops, clams and crabs. We can only guess at the impact declining shark numbers have on parts of the ecosystem that do not affect us directly. Read the rest of this entry »
Sharks are the focus of a wide range of medical research and a source of biomaterials used in several surgeries and pharmaceutical drugs. For example, the irregular, shifting structure of sharkskin that deters plant spores from latching onto and growing on sharks is being studied for possible medical applications. A sharkskin-like surface would prevent detrimental tissue growth on biomedical implants like catheters and heart valves. Scientists are also studying how Epaulette sharks can survive being stranded on shore for a few hours at low tide without being able to breathe. Since the epaulettes cope with oxygen deprivation at temperatures close to the human body temperature, there is hope that what they learn could be applied to stroke and heart attack patients.
Humans are swiftly wiping out sharks. The United Nations Environment Programme estimates that as many as 100 million sharks are killed each year, and that global populations have dropped by up to 90% in the past few decades. Certain species are on the verge of extinction or already extinct in some regions.
Here’s some other shark adaptations:
- Swell sharks can inflate their stomachs with water, increasing their diameter by up to 3 times their normal size. This sudden size increase can startle predators or help the shark to wedge itself in a crevice on a reefbed, making it hard for predators to remove it.
- Juvenile Nurse sharks prop themselves up on their side fins and curl the fins under themselves to create a false cave that unsuspecting crabs seek refuge in. The sharks promptly eat any tricked crabs.
- The way an Epaulette shark’s side fins are attached to its body allow it to maneuver its fins in a type of “walking” motion over coral and rock beds.
- Read the rest of this entry »
Here’s some more ways that sharks are diverse:
Sharks come in a wide range of sizes. Dwarf Dogfish are the smallest, reaching a max length of only 8 inches. Whale sharks are the largest. The biggest one actually measured was 42 feet, though there are estimates that they reach up to 60 feet. While there are several other sharks that grow to be close to or more than 20 feet long, most reach more moderate lengths. About half of known shark species are under 3 feet long, and eighty percent don’t exceed 9 feet.
There are over 500 different types of shark. Each has evolved with a specific tooth structure, skin pattern, body type and other traits to suit them to living in a specific niche and hunting a certain range of prey. Here’s a quick overview of some sharks and their adaptations to give you an idea of how diverse they are:
Some sharks, like Makos, have pointy teeth that are perfect for impaling and trapping fast, slippery fish. Others, such as Whites, have serrated teeth for tearing through and removing chunks of meat from blubbery sea mammals. Bottom dwelling sharks, like Port Jacksons, sport flat teeth that can crush shells or exoskeletons. The three filter feeding sharks—Whale, Megamouth and Basking—have minuscule teeth that are essentially useless for catching prey, but the spongy tissue along their gills can sieve tons of zooplankton from the ocean as they swim with their mouths open. White Spotted Bamboo sharks have extra versatile teeth—not only are they pointed to pierce and grasp fish, but the ligaments that attach the teeth to the jaw are unusually flexible to allow the teeth to fold back under pressure, becoming a flat surface that can crush hard shelled creatures. The small, parasitic Cookie Cutter shark attaches itself to large fish or marine mammals using its suctorial lips, and then removes a plug of flesh by vibrating its jaws and twisting its body.
Sharks actually have sharp eyesight. Here’s three reasons why sharks have good, if not impressive, vision:
Sharks have great night vision.
A shark’s eyes are about 10 times more sensitive to light than our own. Like cats and other nocturnal animals, they owe this sensitivity to a mirror-like membrane behind their retinas called the tapetum lucidum. Light is reflected off the tapetum lucidum, back to the photoreceptors in the retina, effectively reusing and thus doubling the amount of light that reaches the eye’s photoreceptors. This is why sharks are so adept at hunting after dark, even with only starlight to illuminate the ocean. Because of their high sensitivity to light, sharks have also evolved a way to avoid being blinded in bright light conditions. They have mobile pigment cells in their eyes called melanoblasts. Melanoblasts cover the tapetum lucidum when light levels get too intense. It’s kinda like wearing those Transitions brand eyeglasses that darken or lighten in response to light levels.