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Hi Reader, Do you have a fear of Sharks? Many that are unfamiliar with life under the sea, and unfamiliar with sharks in particular, do. Sharks are strong powerful predators and deserving of our respect for their capabilities.
The nurse shark is likely the most misunderstood of all the sharks. It offers the opportunity to begin looking a sharks in a new light. Through its example, we can begin to transform fear into reality and begin to more fully understand the animal that we’re diving with.
While most sharks use strength and speed to chase down prey, the nurses shark embodies waiting, sensing, and conserving energy. It spends most of its time, especially during the day, resting and sleeping. Sometimes referred to as the ocean’s sleeping dragons, they are ancient and patient predators that survive, not through speed and constant movement, but through stillness. Comparing its tail to a typical reef shark, the nurse shark’s tall is adapted to bottom dwelling instead of the constant swimming most sharks need to do in order to keep water and oxygen flowing over their gills
Eyes – Despite their small eyes, the nurse sharks possess exceptional night vision due to a biological adaptation shared with cats called the tapetum lucidum—a layer of reflective crystals behind the retina that bounces available light back through the eye. The eyes also have a nictitating membrane (a transparent protective eyelid) that keeps their eyes safe while hunting in rocky crevices without losing visibility. Spiracle – There is a small hole behind its eye (called a spiracle) which is used to pump oxygenated water over the gills even while the shark has its mouth closed, has its head buried in the sand or while it is sleeping. Barbels – This shark has highly sensitive taste and touch organs call barbels. The shark will drag these ‘wiskers’ through the sand to help them locate prey. Ampullae of Lorenzini – The small black pits around the mouth are the sharks electro-sense receptors. They contain jelly-filled canals that can detect the faint electric fields generated by all living organisms. The nurse shark can use this sensory information to execute precise strikes and suction-capture a meals in dark and murky water. With these tools, the nurse shark transforms into an active hunter at night. They literally taste and sense the night. They patrol reefs using smell, electro-reception, touch and low light vision. As a predator, it doesn’t use high speed attacks to capture its prey. Instead it uses powerful suction feeding. Nurse sharks are generally calm around divers. They can recognize feeding areas and repetitive diver behavior. Nurse sharks will often join divers during the day, especially if they have been fed lion fish during a diver’s hunt or recognize an opportunity for an easy handout. These sharks display some of their most aggressive and violent behavior during mating. Males will bite females to hold position. Eggs hatch inside the mother and she gives birth to live young. They can produce litters of 20 to 40 pups. Diving with these sharks allows us to see the grace and calmness of these animals. We enjoy diving with them and they often seem to enjoy being around us. It also allows us to take a more realistic perspective of all sharks. At some point in all of our dive careers, we move from being afraid of sharks to complete appreciation of their gracefulness, strength, and capability, and can’t wait to get into the water to dive with them. Diving with nurse sharks can be that 1st step to a transition from fear to appreciation. You can see the full video in YouTube from our Cozumel SeaLife Series.
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