Science update

The crew on R/V Rahiti Tane (RT) have used Pacific weather to deploy their instruments over board. Footage of abundant nocturnal plankton right under the hull (if the term applies appropriately) of the raft was obtained. Specimen samples from this section of the water column have been collected with the plankton net featured in previous publications. The pictures portray one cnidarian, or medusa, located around 10m deep at 0100h local time. Large dorados are curious but shy to the staging strobes of the Sperre Deepbot and so are squid and other fish whose silhouette can be seen from the surface only. The guts and blood of a recently caught dorado were used as an attraction for large predators, but none showed up. Calm wind conditions allowed the crew for more activities.

In a beaufort 0 sea state, the sea surface mirrors clouds when seen from above or fish and plankton from below the water. Diurunal plankton that are not very afraid of being eaten in plain daylight, are easy to spot. The neuston and pleuston are groups within plankton that drift on or right underneath, respectively, the surface; they sail with the wind. A flat sea allowed the observer to easily spot some species in these groups. The siphonophore man'owar is commonly encountered in the sea, but also on board RT. There are others like that jellyfish portrayed in the picture next to the raft. That day, a navy of hundreds of individuals surrounded the vessel. However, a stationary raft allowed for more.

Five stones attached to a CTD were casted down from the port side of RT. A time lapse of the enduring actvivity was taken from the mast, and one photo is shared. An electric motor is installed in the rafts center. It assists with the retrieval of instruments. One member creates tension on the spool side, starboard, of the motor. Another one loops the excess because the line is retrieved faster than it is rolled into the bobbin. This is specially noticeable when all the line, approx 3.5km, is out and each coil is around the bobbins axel diameter only. One more rotates the bobbin by the sail to store the line. This process improves everytime and the crew becomes more and more experienced in deep casting. 2.8km of water where profiled. The stones came back full of sand and the bathymetric map indicates a depth between 2.7 and 3.1km. A sunset clean to the horizon, with stratocumulus clouds at mid heights, dorados jumping in the background, and a warm fish dinner were the reward for the hard working crew.

By: Pedro De La Torre, 13th February 2016.