Last night, the sea conditions thankfully calmed down to slight 1m swell with a light wind of 2-4 knots. Through the fog patches of the early hours the mid-water trawl (RMT) was deployed 4 times.
The nets of the first trawl were opened at 150m and closed at 100m. The opening and closing of the nets is controlled by acoustic command to avoid contamination of the catch with animals from different depths.
The first trawl brought in a varied catch abundant in winged pteropods. The second trawl, from 550m to 450m, was dominated by euphausids (Krill) and mysid shrimp. The third trawl sampled from 350m – 250m and the fourth from 75m to the surface. The fourth trawl contained a lot of myctophid fish and decapods.
This haul of myctophid fish was welcomed by Birkir Bardarson, University of St Andrews, who squeezed them into a Perspex T-Tube to measure the velocity of sound through their bodies. The ratio of the sound velocity in seawater to the sound velocity through creatures within the water column will be used to interpret results from echo sounding surveys.
The invertebrates from the catches were sorted into dominant groups and preserved using a variety of methods including freezing at -80 C, flash freezing in liquid nitrogen at -200 C and preserving in formaldehyde. These preservation techniques allow for molecular analysis looking at the genetics and the trophic levels of the various species. This will be done by Tom Letessier, University of St Andrews, for his PhD.
These catches provide an image of the vertical distribution of fauna in the pelagic realm. They also serve to ground truth the data from the EK60 echo sounding profiles.
After breakfast the NE mooring was deployed by the SAMS team. This reaches from the seafloor to 200m below the surface and includes an upward looking ADCP, 2 sediment traps and 6 current meters. This will be recovered in a year.
After lunch, following the same procedure for all the superstations, the PALander and the amphipod trap were deployed, followed by a CTD and optics cast (see previous blog entries for more details)
The following photos give an idea of some of the animals that we have found during this cruise from the sea surface to the seafloor:
PhD student, Oceanlab