Mike Dunford is a graduate student in the Department of Zoology at the University of Hawaii, Manoa, where he studies evolution. He's also a contributer to 
Last Tuesday, I posted another one of my picture quizzes, asking what a particular device is, and what it's used for. Jonathan was the first to get the correct answer - it's a Niskin bottle. A Niskin bottle is used to collect a sample of water at a particular depth. It's put into the water with both ends open, so that water flows through it freely as it descends. When it reaches the desired depth, the two ends are sealed and water trapped inside. As Dave S. notes, the bottle in the picture is a small one, and it's being used in a low-tech setup.
The picture was taken during a field trip that was part of the Marine Ecology and Evolution course (Biol 301) at UH Manoa during the Spring, 2005 semester. The field trip was a half-day excursion on the R/V Klaus Wyrtki. The Wyrtki is a converted 57 foot long-line fishing boat that's operated by the UH Manoa School of Ocean and Earth Science and Technology, and is used primarily for short research trips in Hawaiian waters.
To give you a sense of how quickly you reach deep water off the coast of the Hawaiian Islands, the Niskin bottle that is visible in the picture is part of a string that sampled water down to about the 1000 foot mark. The land that you can see is not the closest portion of the shore - at the time, we were less than 2.5 miles from the coast.
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