Quarterdeck Volume 6, Number 1, May 1998
Capture a slice of sea life
Net system samples species at nine depths
Knowing the kinds and amounts of fish, squid, and shrimp in the gulf's Deep Scattering Layers (DSLs) is key to our inventory of the sperm whales' habitat. Although our acoustic Doppler current profiler (ADCP) shows these organisms scattering sound in the water column, the ADCP cannot tell us what the organisms are. To find out, we collect actual specimens from discrete depths.
Our collection tool is the electronic Multiple Opening/Closing Net and Environmental Sampling System. The MOCNESS has nine cone-shaped nets, each with a mouth area of one square meter. We lower the MOCNESS from the ship at the end of a conducting cable, which allows the operator to receive real-time data and lets us send commands to the MOCNESS. We tow the nets at one and a half to two knots.
As the MOCNESS is lowered into the water, the first net is open. When the cable operator has released enough conducting cable wire to reach a depth of interest, a net command closes the first net and opens the second net. We can maintain the position of the net within a depth range as thin as five meters or less, depending on wave and weather conditions. When a flowmeter in the net's opening has measured 300-500 cubic meters of water filtering through the net, another net command closes the second net and opens the third net. In this manner we can open and close nine nets which can be from a constant depth or from a 10-25 meter interval. After returning to the surface, the nets are rinsed down and the samples preserved in 10 percent formalin for laboratory study.
In addition to the MOCNESS, we also tow a larger Isaacs-Kidd Midwater Trawl, in order to sample the larger, faster animals that might avoid the MOCNESS nets. The IKMT has a mouth area of six square meters, and we can tow it at a speed of four to five knots.
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Last updated May 1, 1998