Monday, June 04, 2007

Maug and Uracas, our farthest north

With Maug and Uracas behind us we have reached the northern limit of our mission and are on our way south and home. Our three days at Maug were some of the most spectacular diving of the cruise. Crystal clear waters and wall plunging hundreds of feet into the blue. Diving, hiking, and a little relaxation were all welcome rest-bits from our otherwise non-stop operations. Maug is made up of three islands ringing a central lagoon more than 500 feet deep. Inside this lagoon, hydrogen sulfide still bubbles from the sand, a reminder that these islands were not always the calm and peaceful waters that greeted us. Our oceanography team spent the better part of a day collecting these tiny bubbles for later analysis.

Uracas served as yet another reminder. While the underwater world was not as spectacular as that of Maug, the above water sights were from another world. Uracas is a grey cinder cone, a over-turned ice cream cone in the middle of the pacific. Constant rock falls and avalanches down it's sides kept plumes of dust drifting through the air. During one of our tows, a section of cliff the size of our boat broke loose and came crashing to the beach hundreds of feet below. It certainly gave us something to look at during the hour long surface interval we have while the other team was in the water.

Uracas also gave me one of my most exciting experiences of the mission when a six foot tuna came to check out my fins during an afternoon dive. Jake and I were collecting Crown of Thorns starfish arms for genetic analysis and photographing the reef when I saw several Dogtooth tuna swimming in deep water. I slowly swam out to meet them as the largest of the group started to angle my way. I stopped and slowly raised the camera to my mask as he glided effortlessly towards me. He came to within two feet of my fin tips before circling around behind and slowly moving away. It was awe-inspiring to say the least.

Tom Schilis contributed photographs to this article

Close Encounters at Maug Islands

It was our first day at Maug, near the northern extreme of the Marianas Archipelago. The three wall-like (~800 ft tall) islands that comprise Maug form the rim of an ancient volcano, with three passages to a deep (to nearly 1,000 ft) lagoon or submerged caldera. These high islands are spectacularly scenic, with a pre-history feel. Our first dive was fairly routine- a seascape of large volcanic boulders, with small colonizing corals, scattered across black sand. The coral reef on our second dive, outside of North Island, was simply gorgeous- one of the best in the Marianas- high cover of diverse, large multi-colored corals, abundant fish of all sizes, and great visibility, nearly as good as it gets underwater. I was conducting stationary point counts of medium-large fish on the seaward reef slope, while my buddy did the same a short-distance shoreward. After recording a few large fish, I noticed a shark swimming straight at me. I didn’t realize its size till it turned just in front of me- a 5-foot gray-reef shark (Carhcarhinus amblyrhynchus), followed closely behind by another fat 6-footer, as well as a giant trevally (Caranx ignobilis). As I recorded these on my data sheet, I noticed them swimming around me. My first impression was- wow- great photo opportunity. As I prepared my camera I began moving backwards to fit them in the frame. The one closest to me was then swimming on its side with its body contorted and shaking. I then thought- poor thing, it must be sick or something. It had been some time since I had seen many grey reef sharks, as they seem to becoming rarer each year in the remote Pacific Islands. As I quickly fired a few shots with my camera, I had a flashback of my earlier years of diving with these grays in the Northwestern Hawaiian Islands: the shark was exhibiting aggressive pre-attack posturing behavior! As it opened its jaws wide while violently thrashing his head back and forth, I immediately began moving back toward my dive buddy. The sharks then left. The remainder of the dive was less eventful, with only a 5-foot white-tip shark (Triaenodon obesus) and several great barracuda (Sphyraena barracuda), plus all the other beautiful marine life that comprised this healthy coral reef ecosystem.

Text and photographs by: Bob Schroeder, Chief Scientist