MOCNESS 1-Meter2 Towing Procedure for GLOBEC Broad-scale Cruises

1. The 1-meter2 MOCNESS (MOC-1) sampler is loaded with ten nets. Nets #1-4 are 150µm mesh, and nets #0,5-9 are 335µm mesh.

2. MOC-1 tows are double oblique from surface to ~5 meters off bottom. Maximum tow depth of nets #0 and #5 is 500 meters. Net #5 is brought up from maximum depth to 200 meters whereupon net #5 is closed and net #6 is opened.

A standard tow is as follows:

NET MESH(µm) RATE(m/min) STRATA(m)
0 335 15m/min Down - from surf to maximum depth or 500 meters.
1 150 15m/min Up - from max tow depth to 100m.
2 150 15m/min Up - from 100m to 40m.
3 150 15m/min Up - from 40m to 15m.
4 150 15m/min Up - from 15m to surface.
5 335 15m/min Down - from surface to maximum depth or 500 meters, then up to 200 meters.
6 335 10m/min Up - from max or 200m to 100m.
7 335 10m/min Up - from 100m to 40m.
8 335 10m/min Up - from 40m to 15m.
9 335 10m/min Up - from 15m to surface. This net remains open at end of tow.

3. Winch rates for nets #0-5 are 15 m/min and for nets #6-9 10m/min at depths 200m. For those nets fished >200m, the decent rate can be increased so the maximum vertical velocity of the MOCNESS(not the winch rate)is 25m/min. This is providing the net angle does not go below 25 and the net horizontal speed does not drop below 0.5 kts. After maximum depth is reached and the MOCNESS is hauled back, the assent rate should not exceed 10m/min vertical velocity. Note that from 200m to the surface, standard winch speed rates are to be used.

4. During the tow, nets are tripped "on the fly" and the computer command is initiated about two meters from the next designated depth stratum to be fished. For example, when a net fishing on the up haul within the 100 to 40-meter stratum reaches 42 meters, trip the next net.

5. At the end of the first oblique haul (#0-4), when the MOC-1 is at the surface, trip any remaining nets of 150 m mesh ( #4) so that net #5 (with 335 m mesh)is fished on the down cast of the second oblique cast.

6. On completion of the second oblique cast (nets #5-9), when the MOC-1 is again at the surface, close the net fished to both minimize surface sampling and to end data acquisition. The exception is if #9 net is the last net fished, it of course cannot be closed (just mouse click "end acquisition" in program) before the MOC-1 is retrieved back aboard.

7. At stations where water depth is such that subtraction of the ~5-meter off bottom safety factor results in only a few meters of depth to be sampled, the current protocol is to not fish a net for only one or two meters, but to fish a net for a 3-m or greater stratum.

Last modified: January 30, 1998 (Sibunka/Wiebe)