BONGO Sampler Towing Procedure For
Globec Broadscale Cruises
For table of water depth, sampling depth, maximum wire out
and wire speed click here.
Feb. 1, 1995
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- Gently hose net contents into corresponding sieve. Tie cod
ends in preparation for next station.
- 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.
- Store jar in cardboard container.