Photo of the Week: January 11, 2010

Hi Gang!

This week’s POTW is a picture of a tiger shark (Galeocerdo cuvier), a species that most divers recognize almost instantaneously because of the vertical stripes, spots and striations on their back and sides. No doubt about it, a big tiger shark is an imposing animal, and the tiger shark is one of those animals that captures our imaginations when we think about the marine kingdom, and that commands our undivided attention when we see one underwater.

Tiger sharks are held in high regard by many native Hawaiians because they believe the spirit of their ancestors manifest themselves in living tiger sharks.

With the exception of the Mediterranean Sea tiger sharks inhabit all of the world’s tropical and temperate bodies of water. Individual animals are documented to cover long distances. In fact, tiger sharks have been documented to travel over 50 miles in a 24-hour period. They are generally believed to prefer shallow, coastal water that is somewhat murky.

Tiger sharks are seasonal migrators moving toward tropical areas during the winter and toward cooler, temperate seas during warmer months. While they often appear to be slow and lumbering in the water, tigers can change their demeanor at a moment’s notice, taking on the personality of swift, aggressive predators.

Few would debate that it is their combination of size, power and predatory skills that makes tiger sharks a topic of interest for many divers. Tiger sharks feed on a very wide range of food sources including marlin and other large bony fishes, marine mammals, turtles, other sharks, squids, octopi, rays, crustaceans and even sea birds. They are also well known to scavenge on trash discarded into the sea by humans. The teeth of tiger sharks are broad at the base, serrated and extremely sharp, a design that is superb for cutting and tearing their prey. The teeth are also very well equipped for crushing the shells of sea turtles, a favorite prey item that would be difficult to impossible for many other sharks to capture and consume due to the hard, thick shells of sea turtle.

Surprisingly perhaps, tiger sharks are known to prey upon unsuspecting sea birds in shallow waters, especially fledgling albatross chicks. Tiger sharks are migratory, but they are documented to gather in areas in the Marshall Islands and French Frigate Shoals in Hawaii when recently hatched albatross chicks attempt their first flights. Many of the young birds only manage to fly a few feet before dropping into the sea where opportunistic tiger sharks await an easy meal.

Tiger sharks often bite with a rolling motion to assist their large, saw-like teeth in cutting, ripping and tearing large prey into smaller pieces so prey items can be consumed. Although they are opportunistic feeders that readily feed when a good opportunity arises, tiger sharks typically hunt at night, often entering surprisingly shallow water very close to shore.

I captured this week’s POTW image at Tiger Beach, a dive site in the Bahamas that is accessible by liveaboard dive boats, and that is well known for the opportunities divers have to dive with tiger sharks and lemon sharks. Over the course of a day conditions at Tiger Beach often vary considerably due to the direction of the tidal flow. An incoming tide brings relatively clean ocean water over the shallow sandy sea floor at Tiger Beach. An outgoing tide often brings dirty water.

I was fortunate to have the right water conditions and a nice, large tiger shark to work with when I captured this week’s POTW. I used a Nikon 17-to-55 mm zoom lens, an excellent lens for working with sharks and other big animals in reasonably clear water because the zoom feature helps me fill a pleasing percentage of my frame with the animal. If I am able to get right next to the shark, I pull back and use a wider focal length. If I am unable to get as close as I might like, but I can still work in the water conditions of the moment, I zoom in a little and get the best image I can get at the moment.

I know shark diving is not every diver’s cup of tea, but for those that want to pursue sharks, there is little question that Tiger Beach provides that opportunity.

I hope you enjoy this week’s POTW.

See you next week!

Marty