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Volume 14, Number 1 • January-February 1996
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A High Tech Fish

It is one thing to speculate on interactions between physics and biology in the Chesapeake, quite another to map their complex relationships.

When researchers intensively studied dissolved oxygen processes in the mid-Bay during the 1980s, they would take a suite of vertical measurements every two meters at 6 locations across a transect be-tween the Choptank and Patuxent rivers. In a day, they might take 36 measurements, among them temperature, salinity, dissolved oxygen and nutrient levels.

These provided them with a series of data points - dots on a graph - from which they drew their mental maps of the Bay's ecology. Now they can, in little more than an hour, take 36,000 salinity measurements, 30,000 dissolved oxygen measurements, 30,000 zooplankton samples. The difference is the advent of new technology, most notably a flying underwater wing called the Scanfish. With this new instrumentation the researchers can see what they could not see before. "The structure of the Bay is much more complex," says researcher Michael Roman. "It surprises you and makes you come up with new theories. It's like seeing satellite photographs for the first time."

[Scanfish]

Scanfish -- a nw underwater flying vehicle -- is enabling scientists to sweep the entire Chesapeake Bay rapidly, taking thousands of measurements that will help UMCES researchers identify whether the Bay has regions of major biological production.

Mechanical fish have been used in the open ocean for some years, says William Boicourt. The most common are the Batfish out of Halifax, Nova Scotia and the Sea Soar out of California - fat jet airplanes with small wings fitted with instruments and towed alongside the research vessel.

For the Bay, the researchers needed something more fit for shallow swimming. In the Scanfish, says Boicourt, "we have something like a stealth bomber, a flying wing."

As the Scanfish is towed, it rises and falls alongside the research vessel, gathering data on temperature, salinity, oxygen and zooplankton. Though optical counters for counting zooplankton have been available for a while, says Michael Roman, in the last several years their sensitivity has increased remarkably. "We see a ticker tape of zooplankton going through, sizes from tiny Acartia tonsa to fish larvae, pockets of critters even at low oxygen that we missed before," he says. "I get more data now in one cruise than I have in 25 years."

Using the Scanfish, the research team covers the Bay twice over ten days, from its mouth to the Chesapeake and Delaware Canal, sampling 26 to 28 transects. On the first cruise, the crew uses the Scanfish and fish acoustics, mapping as they go, capturing as many variables as possible, as fast as possible. "Three days," says Boicourt. "And we don't stop."

Then the ship returns to the UMCES' Bay labs at Horn Point and Solomons to change crews. The boat travels again to the Bay mouth, hitting every other criss-cross - now with 12 in the scientific party, as many as the research vessel Henlopen will hold. On this second leg, researchers take process measurements, calibrating production, catching fish to positively identify species. Fisheries scientist Ed Houde trawls for fish - he wants to know species and size distributions, what the fish eat, and if there are correlations between the physical features and the way these fish and their prey are organized.

"We want to be able to examine growth rates," Houde says, "to see if fronts promote growth or if they simply aggregate fish and predators together or if there is even a net benefit at all."

"In the dissolved oxygen project, we learned a good deal," says Michael Roman, "but we were connecting the dots between measurements with our best calculations." The inferences that researchers could draw about small-scale fronts and other circulation features were limited. Now instruments on the Scanfish are filling in the dots with real measurements - and helping UMCES scientists to see more than they ever could before.




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