FOCI Standard Operating Instructions

January 2002
3.2.9 Tucker Trawls - The Tucker trawl may be used as the primary gear for late-larval surveys, as a backup for the Multiple Opening/Closing Net Environmental Sensing System (MOCNESS), or for dedicated predator studies.  When used for late-larval surveys, the Tucker will be equipped with 0.505-mm mesh netting and be towed in a smooth oblique fashion with one net open.  If the Tucker is to be used as a backup MOCNESS sampler, it will have 0.333-mm mesh netting.  However, four Tucker tows are required to substitute for one oblique MOCNESS tow.  When used for predator studies, it will have 0.505-mm mesh with a 1-mm cod-end bucket.  When used for discrete depth sampling, a Sea-Bird Electronics SBE 19 SEACAT or a SBE 39 Temperature and Pressure Recorder will be attached on the main cable above the bridle.  The messenger release is positioned on the cable above the SEACAT.

The winch should be one of the ship’s Markey oceanographic winches equipped with slip rings and at least 2,000 meters of 0.322, 2-layer, 3-conductor oceanographic wire.  A Sea-Bird Electronics SBE 19 SEACAT Profiler or SBE 39 Temperature and Pressure Recorder will be attached to the wire above the bongo frame(s) to provide real-time tow data.  The primary SEACAT, or SBE 39, will be provided by the Pacific Marine Environmental Laboratory (PMEL) and the backup SEACAT will be provided by the ship.  Before the SEACAT is terminated on the wire by the ship’s electronic technician and the survey technician, a PMEL scientist will note the identification number of the unit and provide the proper calibration file for the computer when the SEACAT from PMEL is used; however, if the ship’s equipment is used, current calibrations should be available.  Personnel from PMEL will provide the acquisition computer and monitor.  There is no requirement for the SEACAT data to be displayed on the Scientific Computer System (SCS).

After the bridge gives permission, the survey technician and one or two scientists will deploy and recover the Tucker trawl.  A scientist will be stationed in the ship’s DataPlot compartment to monitor the SEACAT and to inform the ship’s survey technician and winch operator when each desired gear depth is reached.  While holding at depth, the first messenger is sent, usually by a scientist, closing the drogue net and opening the first net.  Then at the next desired depth, a second messenger is sent, closing the first net and opening the second.   The winch operator will be instructed by the scientist from DataPlot to retrieve the nets at a wire speed of 20 meters per minute.  The ship’s speed should be adjusted to maintain a wire angle of 45(±5)° during the entire tow, which is accomplished by the survey technician relaying wire angles to the bridge by radio.  When the nets reach the surface, they are brought aboard and hosed with saltwater to wash the sample into the cod-end.  The sample is preserved as specified in the FOCI Field Manual or sample collection request forms.  Flow meters in the nets record the amount of water filtered, and the SBE 19 SEACAT, or SBE 39, records the depth history of the tow.  The scientists on watch are responsible for recording times, maximum depth, wire outs, and flow meter counts on the Cruise Operations Database (COD) forms.  Tows not meeting specifications (i.e., hit bottom, poor wire angles, nets tangled, etc.) may be repeated at the discretion of the scientific watch.

allen.macklin@noaa.gov