Why is the sea blue?

by B. N. Sullivan

The Right Blue - Bloody Bay Wall, Little CaymanThe name of this blog is The Right Blue, and as we explain on our About page, that term refers to a quest:
Sea water viewed from beneath the surface comes in many hues and shades. Surfers wait for the perfect wave; divers seek the right blue.
By the way, the color of the water in the photo on this page is just about as close to 'the right blue' as we've ever seen. The picture was shot at a dive site called Bloody Bay Wall, on the northern shore of Little Cayman, Cayman Islands. The image was scanned from a transparency (slide), but the color has not been tinkered with at all.

So why does the sea look blue? And why does it sometimes look not-so-blue, or even green?

The sea looks blue for the same reason the sky looks blue: the refraction and scattering of light rays. Light scatters as it passes through air or water. Since blue light has a short wavelength, it scatters most easily. Conversely, red light has a long wavelength and scatters less easily. So, the blue rays get reflected back, and that's what we 'see' as the color of the sky or the water surface.

Notice I said water surface. So far I'm talking about what color a body of water appears to be when viewed from the shoreline, or from the deck of a boat.

Water viewed from beneath the surface appears in different shades depending on the depth, and on how much particulate matter is suspended in it. If you descend just a few meters in clear water on a sunny day and then look up toward the surface, the water will look almost transparent with perhaps a tinge of blue. Descend a few more meters and look up toward the surface again, and the apparent color will seem more blue. Descend below, say 25 meters, and you will see something approaching the color of the water in the photo above.

If the water has a lot of 'stuff' in it -- stirred up sand, or plankton, or tiny bits of debris -- some of the light will be deflected. The water will look less transparent -- possibly even murky. Likewise, if the sky above is overcast, even clear water will sometimes seem grayish from below.

As a rule of thumb, the deeper you dive, the darker the water appears, because fewer light rays are able to penetrate the depths. On night dives, there is no ambient light under the surface, so everything is inky black. Divers use artificial light from a flashlight or spotlight to illuminate a small area at depth, or during a night dive.

Have you seen any sharks?

by B. N. Sullivan

We decided that the first post about marine life in this blog should be about a shark. Our reason is simple. When new acquaintances learn that we are divers, one of the first questions we are asked is, "Have you seen any sharks?"

The answer to that question is an unqualified YES. We have seen many, many sharks over the years: Little sharks, big sharks, juveniles and adults. We've never seen a great white shark while diving, but we have encountered whale sharks, gray reef sharks, blacktip reef sharks, silvertip sharks, nurse sharks, Caribbean reef sharks, leopard sharks, several kinds of hammerheads, one tiger shark, one Galapagos shark, one thresher, and possibly a few other species that we have forgotten for the moment.

The shark species we have encountered most often is the one in the photo on this page: the whitetip reef shark (Triaenodon obesus; Hawaiian name: mano lalakea). This species is widely distributed in the waters where we have done most of our diving.

The individual in the image above was photographed at Sipadan, an oceanic island off the coast of the Malaysian end of Borneo in the Celebes Sea. The photo was taken near the southern tip of the island on a gentle slope about 20 meters (60+ ft) deep, covered with sand and coral rubble -- and several dozen whitetip reef sharks at rest. It was quite a sight!

This individual was a bit apart from the rest, making it easier to approach for a portrait. Even after I shot off several frames, blasting the poor shark with flashes of light from the strobes each time, it did not leave. (In case you are wondering, that's a remora -- AKA 'sharksucker' -- on the back of the shark.)

Whitetip reef sharks are not considered to be particularly dangerous to divers -- unless the diver has been spearfishing, in which case whitetips have been known to sneak up and snatch away the diver's catch. We don't spearfish, so we haven't had that experience.

During daylight dives, whitetip reef sharks often are encountered at rest in cavelets or sheltered areas of reefs, sometimes in small groups, but usually as individuals. When not at rest, these sharks can be seen swimming over sandy bottoms or a foot or two above a reef. With their slender bodies, they look very sleek as they swim. We've been approached by them on many occasions. Usually they just cruise past while clearly looking us over. Sometimes they pass, and then lazily circle back for another look.

As docile as whitetip reef sharks may seem in the day, they are anything but docile when pursuing prey. On more than one night dive we have seen a whitetip reef shark streak past and nail a snoozing critter so quickly it could take your breath away. And they have no compunction about bashing the coral to grab their prey!

Whitetip reef sharks are creatures of habit, at least when it comes to their napping. A diver making a single visit to a reef may be lucky enough to chance upon a whitetip reef shark, but divers who frequent the same reef over and over (as we have done in our home waters) often learn where these sharks hang out. Once a whitetip reef shark's favorite spot is discovered, divers can return again and again on successive dives and quite reliably find the same individuals in the same cavelet or on the same shelf on any given day.

We have always enjoyed seeing these animals, day or night, whether they are swimming, hunting, or peacefully at rest.

Learning underwater photography -- the easy parts

Nikonos V underwater cameraby B. N. Sullivan

A lot of the tales that will be told in this blog will center on a photo, or series of photos, that I've taken underwater.  I came late to photography as a hobby -- underwater and otherwise. Until the late 1980s, I had never taken any photos except for the usual family stuff -- holidays, birthday parties, trips -- and always with a point-and-shoot camera.

From the time I began diving in the early 1970s, I had often wished I could show non-divers the wonderful things I saw on my dives. I'm usually pretty good with words, but in so many ways there were just no words to describe the stunning scenery or the fascinating critters I saw beneath the surface of the sea. So, I began to think about getting an underwater camera. I couldn't afford a "good" one until the late 1980s, when I bought my first Nikonos V camera body and a submersible 35mm lens for it, just like the one in the photo above.

My first attempts at underwater photography were truly dismal. I understood nothing about photography, and even after reading a few how-to books, I still couldn't figure out how to adapt terrestrial photography techniques to the undersea realm. I sorely needed some instruction.

I heard about a week-long underwater photography course taught by the renowned underwater photographer Jim Church. The course was taught on a live-aboard dive boat in the Cayman Islands, so it served as a diving vacation as well as an opportunity to learn about underwater photography. We both enrolled.

The first day was a shock as we watched all the other "students" arrive toting multiple Pelican cases filled with massive amounts of camera gear. I wilted. We showed up for the course with the one camera and one lens between us. We felt so naive!

Jim Church, bless him, put us at ease from the start. On the first day, he chatted with each of his students in order to get a fix on how much they already knew, and what they hoped to learn during the week. I admitted that I was a rank novice -- and apparently gravely under-equipped at that. Jim patted me on the shoulder and told me not to worry: He said that meant I didn't have any bad habits to unlearn. As for the lack of equipment, there was a whole range of cameras, lenses, strobes and various accessories for rent aboard the dive boat. I tried them all!

Each day we learned a new technique or two in our ad hoc classroom -- the vessel's dining room. Then we went right into the water to practice what we'd learned -- five dives each day, shooting scenes, fish, critters, divers. And speaking of photographing divers, we even learned a lot about managing -- and being -- an underwater model.

We'd do wide angle shots one day, macro shots the next, and so on. We shot in natural light; then we tried out different combinations of lenses and strobes. We shot in morning light, afternoon light, and on night dives.

At the end of each dive, we'd turn in our film for immediate processing. In the evening we'd all sit around the light tables in the dining room looking at our day's worth of slides, critiquing each other's work.

The week went by quickly, yet we learned an enormous amount about photography, camera maintenance, and how to deal with the underwater environment as a "studio" from Jim and his then-sidekick, Mike Mesgleski. [Side Note: Jim Church passed away in 2002. Mike is still teaching underwater photography -- highly recommended!]
It was a great way to learn about the basics of underwater photography, but unbeknownst to me at the time, choosing lenses, apertures and shutter speeds was the easy part.

As we go along, I'll point out some of the more challenging aspects of underwater photography.

Prologue: The supporting cast

Diver on the surfaceI mentioned in the introduction to The Right Blue that this project is part memoir, and part travelogue. Of course, we didn't do all of those thousands of dives or travel all of those thousands of miles alone.

Over the years we have enjoyed the companionship of many other divers and fellow travelers. In many ways, the stories we will tell here are theirs as well as ours.

We're still in touch with many of our old dive buddies and travel companions, so we decided to tell them about The Right Blue project, and to invite them to participate in whatever way they wish.

We have no doubt that our old friends will be interested to see the photos and read the stories we post here. We have no doubt that this project will evoke memories for them as it does for us. What we are hoping is that they will be inspired to add to what we have to say by sharing some of their photos, adding their versions to our stories -- and telling some of their own tales as well.

At the very least, we are asking our old friends to add their comments to the blog posts, and to give us permission to post some photos we have of them. At best, we're hoping that we can convince our lifelong friends to contribute some of their own photos, and to write guest posts about their undersea experiences, too.

So here's a shout out to all of our former dive buddies and travel companions (you know who you are!). Dig out your old photos, conjure up your memories and write them down, and then email the lot to us. We'd like nothing better than to turn The Right Blue into a community project.

P.S. That's one of our long-time diver friends in the photo on this page. I wonder if she'll recognize herself and be able to recall when and where the photo was taken...