On-board Diary: Deep-sea sharks at the seamount
Author: Silvia Garcia
Date: July 9, 2011
We start the day with a dive off Punta de Baños, a place also known as "Culo de perro." The seamount is pretty interesting because its southern slope rises two or three meters from the sea bed, harboring numerous gorgonians Leptogorgia sasarmentosa and many other species we'll describe when we analyze the images taken by the divers.
We have lunch early so we can start working with the ROV right away, this time northwest of the study area. We move roughly between 430 and 400 meters depth on a muddy sea bed and rocks begin to appear as we move forward, until we find some rocky walls covered by invertebrates, including various sponges and some gorgonians we can identify and others we will try to identify later on. This dive is special because we’ve seen two deep-sea sharks: a bluntnose sixgill shark Hexanchus griseus and an angular roughshark Oxynotus centrina.
We collect a specimen of hexactinellida, probably a Pheronema carpenteri. During the dive with the ROV, we've observed areas with high density of these sponges on muddy bottoms, to which they anchor themselves by means of long spicules.
We dredge the sandy, detritic sea bed at almost 300 meters depth, to take the samples on board and determine the remnants of animals that comprise it and, if possible, directly observe some of the species that live in the sand. We find numerous brachiopod valves and some small, old corals, among other skeletons and remnants we’ll identify under the microscope.