The gliders have been out on their own for more than a week. In that time they’ve traveled far out to sea, but today the team decided to turn one of them around and bring it almost all the way back home. Being close to shore is actually more dangerous for a glider than being in deep water, but they thought it would be worth the risk to meet up with the krill team’s echosounder and combine the two instruments’ strengths.

Click through the slideshow to learn about the glider’s travels—then check below for a quick look at what the two instruments found together:

This graph helps show how two instruments combine to create a better picture of what’s going on under the water’s surface. To read it, imagine that the glider is flying from left to right on the graph. As it moves slowly along this 1.5-mile track, it dives from the top of the graph to the bottom and measures chlorophyll levels. That gives an estimate of the amount of phytoplankton in the water, and phytoplankton are the main food of krill.

Now imagine the krill team driving their zodiac along the same route. The boat moves along the top of the graph (the surface of the water), and the echosounder detects patches of krill below it. Interestingly, the glider found a fairly high concentration of chlorophyll high in the water on the left side of the graph. The krill team found a patch of krill in deeper water beneath it, but not anywhere else.

“That’s pretty neat to find,” Dr. Kohut said, “that the only place on the whole transect there was krill was underneath the patch of chlorophyll.” The krill may have been resting during the day before swimming up to eat phytoplankton later in the day, Dr. Oliver said, or they may have been feeding on organic material as it drifted downward from the phytoplankton patch.

What’s really interesting about this find is that it couldn’t have happened without putting the two instruments—glider and echosounder—together. If the glider had been on its own, it would have noticed the phytoplankton, but we couldn’t have known whether krill were around to feed on it. On the other hand, if we’d had only the findings from the echosounder we’d have known there were krill around but we wouldn’t know why.