Henry's heart was pounding hard. His air supply was dangerously low, and he knew the three divers inside the wreck must have even less air because their dive was deeper and they were working as they penetrated the wreck. He swam a short way inside, hoping to find some sign of his friends. Finding no trace of them, he became even more anxious. Finally, in desperation, he ascended to the surface, where he blew his whistle to alert the dive boat crew that there was a problem 130 feet below. The captain immediately sprang into action, taking the steps necessary to get a rescue attempt started.

The Great White, on the other hand, is known to be an aggressive predator and has an extremely muscular body, capable of chasing down some of the fastest swimmers in the ocean.  Reaching lengths of up to 20 feet (6 m) and weights of several tons, the Great White’s body is perfectly adapted to a life of predation.

Great White Sharks are known to be highly migratory, with individuals making long migrations every year.  In the eastern Pacific Ocean, Great Whites regularly migrate between Mexico and Hawaii.  In other ocean basins, individuals may migrate even longer distances.  Like in many highly migratory species, the very largest individuals are female.  Great Whites mate via internal fertilization and give live birth to a small number of large young (over three feet/one meter).  Though they give live birth, Great Whites do not connect to their young through a placenta.  Instead, during the gestation period, the mother provides her young with unfertilized eggs that they actively eat for nourishment.  After they are born, young Great Whites are already natural predators, and they eat coastal fishes.  As they grow, their preferred prey also gets larger, and the largest, mature individuals prefer to eat marine mammals, like seals and sea lions.  Great Whites are known to take very deep dives, probably to feed on slow-moving fishes and squids in the cold waters of the deep sea.  Though almost all fishes are cold blooded, Great Whites have a specialized blood vessel structure – called a countercurrent exchanger – that allows them to maintain a body temperature that is higher than the surrounding water.  This adaptation provides them with a major advantage when hunting in cold water by allowing them to move more quickly and intelligently.  It is also particularly advantageous when hunting warm-blooded marine mammals that might otherwise have too much energy for Great Whites to successfully capture them.

The ultimate action camera accessory, the Sidekick is small, low profile and – at 123 grams – weighs less than the GoPro. Its factory-sealed design and clean simple mount allows Sidekick to seamlessly integrate with any GoPro set-up and go wherever a GoPro goes, including 200 feet underwater. Adjustable spot and flood modes give users the flexibility to control the amount of light to create the perfect POV footage. 

nvertebrate life, so the best way to find them is to lookfor their food, which tends to be richest in areas of current. Their large, brightly colored egg ribbons are normally the first clue that they’re nearby. But be warned: Nudibranch photography is highly addictive; once you begin, the quest for tiny treasure can easily take over your diving.

Using a hot-water drill and an underwater robotic vehicle designed, built and operated by a University of Nebraska-Lincoln engineering team, scientists have made new discoveries about Antarctica's geology and biology.