JELNET Protocol for Broad-scale Cruises

Please Be Gentle.
This Net System is Designed to Quantify
Fragile Zooplankton

1. Tows to be made at all Priority 1 stations, weather permitting. At Priority 1 stations where a 10 m MOCNESS trawl is NOT made because of weather conditions, we would especially like the JelNet tow to be made, since it would then be the only sample for large jellies.

2. Tows are vertical, made from the depth of the deepest MOC-10 net, (usually 0-15 m off the bottom) or to 100 m at the deeper stations. It is not necessary to use a flowmeter with these tows; we will calculate volume filtered from mouth diameter and depth. Suggest the winch operator zeros the wire out when the net is at the surface. The wire out, and not the target depth, is the distance value logged at sea and then used to compute the seawater volume filtered by the net.

3. The net may be cast at 20 meters a minute, while it should be retrieved at no more than 5 m/min. Do not allow the net to rest at the surface when retrieving the net because the ship's roll may act to spill a portion of the catch.

4. Getting the catch out of the net: Lean the frame on it's edge and gently rinse the catch down into the codend bucket.

5. Carry the bucket into the wetlab, and place the catch in the transparent tray and view on the light table. Since much of the cast may be fragile (large ctenophores, etc.), it need be examined immediately, before preservation. We would like a count of the large jellies, particularly lobate ctenophores (i.e. Bolinopsis, Mnemiopsis), and an oral / aboral length measurement of all the animals of a given taxa, or a subsample of ten measurements if there is more than ten individuals within a given taxa. Measurements are made with a ruler from underneath the dish. The entire catch should then be preserved in a liter jar in 10% buffered formalin.

6. Label jar and COMPLETE DATASHEET. Please keep these samples in a separate box.

Contact Erich Horgan (ehorgan@whoi.edu or 508-289-3207) for further details.