Home Harbour PartnersAustralian MuseumSydney Larval Fish Project
Sydney Larval Fish Project
Net hanging from the davet and plankton is washed off the sides of the net into the cod-end. Photo: S. Humphreys.
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The day
07:15-07:30 Fish team arrive bright and early at the Museum. Baragula the Museum's research boat is hooked up to a vehicle and loaded with the equipment needed for the day.
08:30 Baragula is launched at Rose Bay boat ramp.
09:00 The plankton net is set up ready for deployment, while Amanda positions the boat at either Diamond Bay or Manly. Today the Manly site is first up. It is important to always check the water depth before starting the plankton tow. The water must be at least 14m deep so the net doesn't hit bottom.
09:15 First plankton tow is started. Each tow takes roughly eighteen minutes.
The plankton tow
The plankton tow used for this project is an oblique tow. This means the net is towed at an angle through the water column, starting at 10m depth and gradually getting shallower over the eighteen minutes until it ends up at the surface. To do this a 50m rope is attached to the net, so the net trails 50m behind the boat at 10m depth. Then every three minutes 10m of rope is pulled back into the boat. A Global Positioning System (GPS) position is taken at the beginning and end of each tow so the exact position of the tow can be recorded.
[drawing of the tow, needs labels but not sure about font size and readability]
The plankton net
The plankton net has a number of important attachments:
- a 'depressor' attached to the bottom of the net. This weights the net so it doesn't float to the surface when a tow begins.
- two floats are attached to a 10m long cable, which is then attached to the top of the net, this makes sure the net doesn't sink below 10m.
- a dive computer, which will gives an underwater depth profile of the net. (The information from each tow is downloaded at the Museum).
- a flowmeter - a reading is taken before deployment and upon retrieval. This allows us to calculate the speed of the net and volume of water that is filtered.
09:35 Once on board, all the attachments are taken off the net. It is then hoisted up using the davit, and the contents are washed into the cod-end (a detachable pocket right at the end of the net), using the deck hose.
Baragula was custom built for the Australian Museum's research purposes, this means lots of deck space for all of the equipment and things like a deck hose, battery operated winch to haul the net in, and davet for hoisting up the net.
09:45 Plankton samples, which contain the tiny fishes as well as a number of other animals and often plants, are preserved in glass jars of formalin. While the net is being washed down Amanda takes the field data (GPS position, weather conditions, time and field number) and writes labels for the jars. Each tow has a specified field number so that when the team sort and identify the samples later they know exactly where and when it was collected.
09:50 First plankton tow is completed. This is repeated twice if the weather conditions remain favourable.
11:30 Fish team drives Baragula to the next site and do another three oblique plankton tows. To make sure the samples collected are 'scientifically useful', the team always tries to do three tows.
14:00 The work is done and it's time for lunch and a swim!
15:00 - 15:30 Team arrives back at the Museum, now for the fun part! The boat and all the equipment that was used for the day must be washed down and cleaned in freshwater.
The rest of the afternoon is spent putting equipment back or making necessary additions or adjustments to the equipment.
Copyright © Australian Museum, 2002
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