Held firmly, but gently, in place by expedition member Jean de Marignac, a young lemon shark turns to nip at the camera. The shark, probably no more than two years old, was soon swimming free after a quick round of tests on dry land.

8:35am, March 22, Atol das Rocas, Brazil -- Young lemon sharks enter Atol das Rocas's protected inlet with rising tides, presumably looking for food and a bit of shelter in the island's interior lagoon. Ebbing tides drain the lagoon, causing the sharks to return to the harsh, surrounding seas.

Just before high tide, I reached the beach with a landing party of researchers focused on capturing juvenile sharks with nets stretched across the narrow inlet. The team waited eagerly for the tide to recede -- for retreating sharks to entangle themselves. Every shark researcher on the small, tightly-guarded island preserve remained constantly mindful of their obligations to preserve the pristine conditions of Atol das Rocas, and to protect its animal residents. One wrong move, one injured shark, one disrupted bird's nest could mean the end of the mission. And in a scientific study dedicated to learning how sharks live and breed in their natural habitats, the loss of even one baby shark would be an unacceptable blow to the accuracy of the mission's data. While I made preparations to document my second "genetic roundup" of young lemon sharks, the research team redied themselves to work hard, work fast, and work extremely carefully. (See our DAY 9 coverage of Mark's first roundup)

The sharks proved to be much less psyched up for research than the researchers. Maybe they remembered their previous experiences in the channel and avoided the area altogether. Perhaps the tides were off. Regardless, our team managed to capture and sample only three sharks at their beachside field lab. After a while, they called it a morning and returned to the ship.

"You have to adapt to situations like this," said Chief Scientist Samuel Gruber, standing on the ship's main deck. "We have problems with our boats; we fix them. We have problems catching sharks; we change locations."

Tomorrow, the crew will, indeed, 'adapt,' moving their operations to several newly-discovered lemon shark pools.

5:58pm, onboard the Research Vessel SEWARD JOHNSON (RVSJ) -- I was warned in advance that our remote research location would be a hard place to describe. It redefines itself as often as the light changes and the tide shifts.

Atol das Rocas formed millions of years ago as the mass of an ancient volcano slipped, eroded, and sank eventually into the sea. Countless generations of mollusks and algae colonized this submerged caldera, living and dying on the calcarious skeletons of the their ancestors. In time, they formed a mile-wide rocky circle that now breaks barely above the surrounding ocean. The Atol das Rocas of today, although lovely to look at, is a forbidding environment of rough rocks, rough water, and brutal equatorial sun.

As isolated as it is, Atol das Rocas still harbors an abundance of wildlife, both above and below the waves. In addition to sharks, a healthy population of sea turtles and countless tropical fishes swim in the island's lagoon and in the surrounding ocean. Above ground, thousands of birds nest on the atoll's sandy knolls...the sound of their calls overpowers even the waves. Egg shells litter the beaches. Young fledglings flap their wings in the wind, preparing for flight.

With a tidal range of six feet, water rages through the atoll's lagoon as high tide shifts to low tide and then back again. Big ocean swells break in the narrow channels. At times it seems that our expedition is as much about battling the atoll's environment as it is about getting down to productive, scientific inquiry. A mis-timed run through the rocky labyrinth could be disastrous for boats, crew or both. More than once, team members have been stranded by the receding water or by the hazards of navigating the channel at night.

1:20am, March 23, onboard the SEWARD JOHNSON -- I have just returned to my room to face a challenge that seems to dwarf the hazards posed by Atol das Rocas. Namely, my room smells (exactly) like two waterlogged guys have been living in it for almost two weeks. But, fatigue, an adaptable nose, and the comforting drone of the RVSJ's engine promise to put me to sleep within the minute.