Academy of Science of the ussr

Gushchin A. V. & Kukuyev E. I

This study is based on the trawl collections, which were made in 1975-1978 in the region of the Mid-Atlantic Ridge from 45^o to 60^o N.

(The map should be here.)

Most tows were made with pelagic fishing trawls. Collections of fishes were made throughout 24-h period at depths from 500 to 1200 m. A few tows were made using a 15 m conical small-mesh net attached to the trawl.

The collection of fishes has been deposited in the Museum of the Atlantic Scientific Research Institute of Fishing Industry and Oceanography (Kaliningrad).

The authors thank colleagues Miloradov G. K., Gomolitsky V. D, Trunov I. A. for their help in collecting of the fishes and for assistance when working over the collection. Further acknowledgement goes to Parin N. V., Bekker, Sazonov Y. I. and Neyolov for the consultations on identification of the fishes.

The fishes recorded in the studying region are listed below. Following the species name are the regions where the species were taken:

1 – from 45^o to 50^o N,

2 – from 50^o to 55^o N,

3 – from 55^o to 60^o N

and index of frequency of occurence:

“ab” means the species occurs in abundance,

“com” means occurs commonly

“r” means the rare occurrence of a species in trawl hauls.

The coordinates of collecting are given after names of the species, which are represented in the collection by single specimen. For all listed species the latitude of collecting is Northern (N) and longitude is Western (W).

Fam. Myctophidae: Protomyctophum arcticum (Lutken) (1-3, r: to the north of 48^o 45^/), Electrona rissoi (Cocco) (1, com: to the south of 49^o 50^/; 3: 56^o 40^/), Benthosema glaciale (Reinhardt) (1, com: to the north of 46^o; 2 and 3, ab), Hygophum benoiti (Cocco) (1, r: to the south of 48^o 50^/), Myctophum punctatum Rafinesque (1 and 2, r: to the north to 56^o 48^/), Symbolophorus veranyi (Moreau) (1: 48^o 45^/, 28^o 11^/), Diaphus holti Taning (1, r: to the south of 50^o), D. rafinesque (Cocco) (1, r: to the south of 49^o 40^/), Lobianchia gemellari (Cocco) (1, r: to the south of 53^o 15^/), L. dofleini (Zugmayer) (1, r: to the south of 49^o 31^/), Lampadena speculigera Goode et Bean (1, com: to the south of 48^o 50^/), Lampanyctus crocodilus (Risso) (1-3 ab: to the north to 57^o), L. ater Taning (1 and 2 r: to the south of 53^o), L. intricarius Taning (1 and 2, r; 3, com: to the north to 57^o 20^/), L. macdonaldi (Goode et Bean) (1 and 2, ab: from 45^o 35^/ to 52^o 18^/), Ceratoscopelus maderensis (Lowe) (1 and 2 r: to the south of 53^o), Notoscopelus bolini Nafpaktitis (1: 48^o 45^/, 28^o 11^/), N. kroeyeri (Malm) ( 1, r; 2, com: occurs from 49^o to 57^o).

Meso- and bathypelagic macroplankton species were predominant in trawl hauls. Fishes of families Myctophidae (18 species), Melanostomiatidae and Searsiidae were present in more collections then any other species. These are typical fauna for deep-water pelageal of the open ocean (Parin, 1979). Species of fam. Gonostomatidae genus Cyclothone used occur with a high degree of consistency as well. Gomolitsky V. D. preliminarily identified 5 species: C. alba, C. braueri. C. microdon, C. pallida and C. pseudopallida. Each one of the families Asronesthidae, Melamphaeidae, Sternoptychidae, Paralepididae etc. is represented by several species. The catch rates of these species have been reduced when changing direction of collecting towards the north. Thus, 18 species of Myctophidae were found at the southern part of the examining region, and number of this species captured in northern waters was reduced to 7. Some species present in southern collections were absent in northern ones. Such ones apparently are limited by the southern waters.

We consider the proper talassobathyal fishes to be effected by the same tendency, though in less extent. This group of the fishes is represented with less diversity by the bottom and bottom-pelagic species of the families Squalidae, Alepocephalidae, Macrouridae, Merlucciidae, Trachichthyidae, Berycidae, Trichiuridae, Gempylidae, Apogonidae. These species are common for the talassobathyal complex (Andriyashev, 1979). There is a resemblance noticed between talassobathyal fauna of the examining region and fauna of the bathyal-pelagic complex off the western coast of Africa (Parin & Golovan, 1976; Golovan, 1978).

The meso- and bathypeladic species comprise 63% of the total number of the listed fishes. The proper talassobathyal species comprise 32%. The rest (5%) belong to the epipelagic fishes of the families Lamnidae, Cetorhinidae, Scomberesocidae and Bramidae.

We undertook an attempt to compute the quantitative ratio of meso- and bathypelagic species at 6 stations. Collections were made using the small-meshed net attached to the fishing trawl. Biomass of the catches was computed roughly proceeding from the distance of the cruise when trawling. No net closing or catch-separating device was used with the net. The sampling procedures were arbitrary and insufficiently repeated. Due to this facts the data derived from the computations is very approximate. Nevertheless results of our computations (5.8 – 81. 5 mg / m³) appeared to be very close to the data obtained by other means in other regions. For instance, biomass of macroplankton fish in the tropical waters of the Pacific Ocean is 2.1 – 33.7 mg / m³. This result is based on the trawl collections made with Isaak-Kidd multi-depth trawl (Parin & Nesis, 1977).

Table
Ratio on biomass (%) of the species of pelagic fish in collections made at 6 stations