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Both Atlantic eel species (Anguilla anguilla and A. rostrata) were collected in the Sargasso Sea during the 1979 cruise of the F. R. V. "Anton Dohrn" and R. V. "Friedrich Heincke". A total of 3,097 0-group larvae were caught during 80 hauls using the Isaacs Kidd Midwater Trawl (55 hauls) and the 9-fold opening and closing net MOCNESS (25 hauls). 11 hauls of the MOCNESS indicated that the larvae showed a preference for the 150-175 m water depth during daytime and for the 50-75 m depth during night. The northern distribution limit seems to coincide with the "18 °C-water" at the sea surface. The Antilla current characterised by higher temperatures and salinities could have been the southern distribution limit. The north-easternmost occurrence of A. anguilla was noted at 50 ° W; the eastern distribution limit of this species could be farther east. The westernmost station at 69 ° W was positive for both species. A. anguilta, therefore, is very likely to occur beyond this area. The easternmost occurrence of A. rostrata was noted at 52°W though sporadic and with increasing abundance towards the west. At the western end of the network of stations the highest concentration of larvae from both species was recorded. Oceanographic investigations reveal that the distribution of the smaller larvae (size-groups < 7 mm and < 10 ram) almost coincides with the assumed spawning area.

Sixteen silver eels (Anguilla anguilla L.) were tagged with pressure-sensing ultrasonic transmitters and tracked for 1 to 152 hours, 12 in the western Mediterranean and 4, treated with pituitary extracts, in the Sargasso Sea. When released on the shelf of the Mediterranean near Gibraltar the eels preferred a course which led them continuously to deeper water. Four specimens released on the Morrocan shelf, reached depths of 350m, continued to swim north or changed their earlier easterly course towards the north. Three eels in the Sargasso Sea showed progress in a southwesterly direction. No influence of tidal stream on the swimming course and speed is obvious except for one eel, released in the Straits of Gibraltar. In the Mediterranean, the eels exhibited conspicuous daily vertical migration downward during dusk and upward during dawn with a mean swimming depth of 196m during darkness, 344m during daylight. Depth preference during night probably varied with the phase of the moon. Maximum swimming depth near Gibraltar as well as in the Sargasso Sea was nearly 700m. The eels in the Mediterranean swam at a mean speed of 0.3 m. s-' and were slower than most eels tracked in northern waters. Differences in the speed and in the directed swimming in the course of the lunar or the solar day are visible.

Abstract,On a section between Bermuda and Puerto Rico, in MarchlApril 1981 Anguilla sp. larvae abundance and hydrographic conditions were studied. The small larvae ( < 7 mm TI) occurred south of 30° N a t the subtropical thermal front and showed peak abundance a t 26" N. At 2 3 O N larvae of all size groups became less abundant. North-south extention of the spawning area was greater than described in the literature. A considerable net avoidance of the larvae during daylight hauls was observed. Lengths of both Anguilla species increased from the north to the peak abundance area in the south and for A . anguillu also from east t o west. Patches with about the fifty fold larvae abundance compared with the surrounding area could be identified. Deeper occurrence of the smallest larvae (T1=4 and 5 mm) compared with older larvae, found in earlier studies could be stated.