The DOBO lander being retrieved
The whalefish. Photo: David Shale
A deep-sea anglerfish
Date:27 July 2004
Author: Alexei Orlov (Russian Federal Research Institute of Fisheries and Oceanography, Moscow), Gui Menezes (Department of Oceanography and Fisheries, University of the Azores, Portugal)
The end of the cruise is closer and closer. The two landers (the DOBO and the third Bergen Acoustic lander) deployed during Leg 1 of the cruise were retrieved with success, which is always an excitement, a relief for those who built these instruments and use them to collect data for their studies.
Trawl catches continue to bring us new discoveries and some strange fish species with bizarre forms. Yesterday a small anglerfish of 4 cm length and 2.7 g weight and a name bigger than itself (whalehead dreamer Lophodolos acanthognathus), was the star of the day. There are only two species in this genus, and they are poorly known. To our knowledge the males of this species are not yet known.
It is well known that most of deep-sea species die during trawl retrieval as a result of barotraumas. The characteristic signs of barotraumas are protruding eyes and everted stomachs, often observed when fishing rockfish (Sebastidae) and grenadiers (Macrouridae) even at depths shallower than 1,000 m. But several recent hauls showed that some typically deep-water species may survive during trawl retrieval and were lifted from deep ocean layers (1,000-3,000 m) to surface alive. Species we observed alive were blackhead salmon Narcetes stomias (habitat depths 1,500-2,300 m), redmouth whalefish Rondeletia loricata (up to 1130 m), slender snipe eel Nemichthys scolopaceus (up to 2,000 m), common fangtooth Anoplogaster cornuta (up to 4,900 m), and pelican eel Eurypharynx pelecanoides (500-7,500 m). Some of them were still alive when we put them in aquarium, and David Shale had opportunity to take excellent photos. Though two fishes (fangtooth and whalefish) showed incredible survivor. They were still alive when we took them out from aquarium and brought to fishlab for photography. The probable reason for this surprising survival of deep-sea fishes is very low speed of trawl retrieval, which helps to avoid barotraumas to some specimens.
Despite that the main task of this part of our cruise is to collect data and material on demersal nekton, we sampled and continue to sample a lot of mesopelagic fishes for our partners interested in mid-water fishes. This will improve the understanding of taxonomy, zoogeography, distribution, and life history patterns of these species in the mid-Atlantic Ridge area. Thus far we observed in our catches representatives of 102 pelagic species. The most speciouse groups of pelagic fishes in the catches are families Stomiidae, Myctophidae, Gonostomatidae, Melamphaeidae, and Sternoptychidae represented by at least 14, 11, 10, 10, and 7 species respectively. Many of the species were photographed and their pictures will be included in MAR-ECO database of fish images.
At this moment it is difficult to make any comparisons between composition of demersal deep-sea ichthyofauna of MAR and that of any other areas of the World Ocean. We are however able to determine some major differences between the catch composition of our catches and deep-water ichthyofauna of the northwestern Pacific continental slope and seamounts (one of authors is familiar with fishes inhabiting Pacific slopes and also Emperor seamounts and Marcus-Necker ridge). The most speciouse families in our MAR catches were grenadiers (Macrouridae) and smooth-heads (Alepocephalidae) while in the NW Pacific these groups are represented by considerably less number of species. In its turn, the most specious deep-water demersal groups in latter area are snailfishes (Liparidae), rockfishes (Sebastidae), eelpouts (Zoarcidae), sculpins (Cottidae), and probably skates (Rajidae). Such distinctions are mostly due to different origins of the ichthyofauna of both regions considered. Though there are number of congeneric species found in both areas, for instance representatives of genera Laemonema, Coryphaenoides, Lepidion, Bathyraja, Etmopterus, Antimora and many others.