Anything in the pots? Baited traps in Southern French Polynesia. Blog 1, setting the traps.
“Anything in the pots?” is a question I am frequently asked by crew of the RV Braveheart and my fellow scientists as we document samples.
They are using the term commercial fishers in Australia and New Zealand often use for baited traps.
We are in remote Southern French Polynesia, part of a biodiversity survey team. More information on the expedition.
The traps are an item of collecting gear the trip organiser (Dr Tom Trnski) has requested I bring along for this expedition. They provide an efficient way of obtaining cryptic and mobile organisms that other methods miss, and can be used at depths divers can’t readily access. Sampling using these traps is a method I, and other staff at the Australian Museum, have been involved with for almost 30 years and which has contributed to the description of over 60 new species.
I’ve brought along two types of traps, a large commercial design with a 10 centimetre diameter opening and a smaller one with a 1 centimetre funnel shaped opening. The smaller trap is filled with fish bait and placed inside the larger one. The larger trap has a clam-shell design so that it can be folded open, to put in the bait or remove the catch.
During the voyage to our sampling localities the crew help me ready the traps for use. First we measure out and untangle rope from the ships supplies. We need lengths approximately three times the depth of the water we intend to set the traps in, such long lengths help negate the effect of currents and wave action on the surface marker buoys that will be tied to the traps left on the bottom. I specify lengths between 30 and 1,000 metres to allow for a range of depths between 10 and 300 metres, with an aim of covering different habitats found at these depths and collecting a cross-section of different organisms attracted to the bait.
Next we use cable ties to attach approximately 8 kilos of weight into each of the larger traps and then inflate the plastic balloon-like marker buoys I’ve also brought with me.
Everything is ready to go, so at the first opportunity we fill the small traps with frozen pilchards that have been provided as bait, fit them inside the larger traps, load all the gear needed into one of the Braveheart’s auxiliary tenders and head off to set the equipment out. The depth of water is checked with a depth-sounder, the appropriate length of rope selected and tied off to a marker buoy, and the trap lowered over the side and the line let out. We record a GPS co-ordinate and some sight marks so the position can be located again and then head off to set the next trap.