BONGO Sampler Towing Procedure For Globec Broadscale Cruises

For table of water depth, sampling depth, maximum wire out and wire speed click here.
  1. The 0.61-meter bongo is towed at each bankwide station. Net mesh is 0.335 mm. Records are kept on the Ichthyoplankton GLOBEC Sample Log. Before each tow record the first five digits of the flowmeter and make certain cod ends of nets are securely tied.
  2. At stations where larval fish specimens are required for biochemical analyses, tow two bongos simultaneously. Bongo frame marked A and B is on top, C and D on bottom. Put cups on flowmeter fins if windy.
  3. Bongo tows are made to within five meters of bottom or to a maximum depth of 200 meters. Consult the following table for wire payout and retrieval rates and maximum wire out, given depth of water.
  4. To achieve the desired smooth-oblique tow profile and avoid loss of or damage to equipment, personnel responsible for the bongo tow must closely monitor the wire angle to insure that it remains throughout the tow at or near 45 degrees.
  5. During tows with slow retrieval, those over depths less than 45m, avoid over sampling surface waters during haul back. When the mouth of the net initially breaks the surface, tell the winch operator to jerk the net out of the water.
  6. If a sudden slackness occurs in the wire shortly before maximum sampling depth is achieved, haul back immediately. The net is on bottom. Most of the time these samples can be saved, with very little or no sand in them, if you act promptly. If a net contains more than ~200ml of sand, wash it out, discard the contents and redo the tow.
  7. At completion of tow, record flowmeter readings on Ichthyoplankton GLOBEC Sample Log. Thoroughly wash down nets. The top outboard net A is for zooplankton/ichthyoplankton analysis, the other(s) provide specimens for RNA/DNA analysis, etc.
  8. Gently hose net contents into corresponding sieve. Tie cod ends in preparation for next station.
  9. Preserve net A plankton in 5% formalin. Fill quart jar no more than 1/3 with plankton, the remainder with sea water and last with 50ml of formalin. Use more than one jar if necessary and record number of jars (splits) on the Ichthyoplankton GLOBEC Sample Log. Place completed label inside jar and outside on lid.
  10. Store jar in cardboard container.
Feb. 1, 1995