The "two" giant blackhead salmons - Narcetes stomias.
Smoothhead - Bellocia michaelsarsi
Marie Tharp in her Lamont Hall office, c.1961.
Date:July 14, 2004
Author: Alexei Orlov (Russian Federal Research Institute of Fisheries and Oceanography, Moscow, Russia) and Gui Menezes (Department of Oceanography and Fisheries, University of the Azores, Horta, Portugal)
We finished the work on the Southern Box with a dive of the ROV Aglantha in a western station, where we were only able to prospect the water column. Unfortunately the ROV had a problem on the umbilical and the dive had to be cancelled at about 1000 m depth before reaching the bottom.
We have conducted six bottom trawl stations and in each the catches always surprise us. A preliminary analysis of the fish sampled in this southern area, indicates the collection of about 1698 specimens, and more than 112 different species belonging to 43 different families. At the end of the 6th trawl station we feel that we caught a representative sample of the ichthyofauna inhabiting this area, on both sides of the rift.
The alepocephalids (smoothheads) are one of the most diverse families in catches taken by bottom trawl within the southern box (16 species). One species in particular, commonly named blackhead salmon (scientific name Narcetes stomias), attracted special attention. The maximum known length of this fish is 57.5 cm. In all the previous trawl catches we dealt with small- or medium-sized individuals. But last trawl brought exactly two giant specimens (see photo), which had total lengths 84 and 86 cm and weights of approximately 5.5 and 6.0 kg respectively. Blackhead salmon inhabit mainly deepwater areas adjacent to the continental slopes of the North Atlantic and Pacific, although several captures are known from the South-western Pacific. Previously only several small specimens of this species were caught within the Mid-Atlantic Ridge area in 1982 by Dr. G. Krefft, northward of our southern box study area (43-45N, 16-23W). Among the smoothead species we caught, another also retains our attention, Bellocia michaelsarsi, a name given in honour of the famous Norwegian zoologist Michael Sars (1805-1869), the father of Georg Ossian Sars (1837-1927) also a famous zoologist and the person for whom the ship is named after.
Another interesting finding is related to the diet of probably the largest ophidiid in this area (up to 127 cm) commonly named pudgy cuskeel (scientific name Spectrunculus grandis, see photos in previous report), which is, according to literature sources, a predatory fish. Drs. Mauchline and Gordon noted that off the Rockall Trough it feeds mostly on squids and bony fishes. We have found in the intestine of our specimen several large (10-15 cm) pyrosomas (gelatinous planctonic organisms) that seem very unusual and suggest that the cuskeel may prey upon these animals in the water column. ROV dive video confirmed this suggestion – we have seen a single cuskeel swimming some distance from the bottom. Further food analysis of specimens frozen for detailed trophic studies ashore, will help us to understand the feeding behaviour of this and other species. No doubt, this was one of the most interesting species caught during the G.O. Sars Leg 2 cruise.
We are steaming to the Middle Box along the Mid Atlantic Ridge, which can be observed by the sophisticated seafloor mapping equipment aboard the G. O. SARS. First glimpses of this ocean basin were revealed fifteen years ago by the pioneers of an earlier day in oceanography. The first detailed 3D maps showing all the ocean basins were produced by Bruce Heezen and Marie Tharp and published in the National Geographic Magazine in 1957 (see photos, and visit the website for details). These maps were created based on a huge number of depth soundings made during the 1940s-1960s using the precision depth recorder (PDR) that equiped several ships at those times. Heezen and Tharp pieced these recordings together to make their now famous map. It was through Tharp's astute observations that the Atlantic Rift Valley was first discovered, which paved the way for acceptance of the theories of plate tectonics and continental drift.
The next area is the Charlie Gibbs Fracture Zone (already described earlier, as a fantastic geological seabed feature). We are all anxious, and have high hopes that we can use the ROV Bathysaurus again for deeper dives on the Charlie Gibbs valley.