— 186 — 



of the sea where the temperature at looo meters depth was at least ca. 7° 

 and the salinity at least ca. 35-20 pro mille. It follows from this that the wide 

 regions of the most northerly Atlantic and all the Northern Ocean are excluded from being 

 the regions where the eel larvae can be found; this is represented on the Chart of distri- 

 bution Plate X showing the temperature-curves for 1000 meters depth. 



(3) Importance of other factors. It can be seen from the Chart Plate X that 

 there is a great difference in the number of eel larvae taken at the different stations. The 

 two stations marked with a large red spot for example gave us without comparison 

 far more eel larvae than any ot the others, as our hauls there (of 2 hours duration) 

 brought in respectively 38 and 70 specimens, whilst at none of the other stations did we 

 obtain more than 8 specimens at most in a 2 hours haul. The reason for this cannot 

 be indicated with absolute certainty, but an examination of the chart gives us an inkling 

 of its meaning. It appears from the Chart that this region lies right off the English 

 Channel through which specially large masses of eels undoubtedly migrate out 

 from the North Sea in search of the depths, temperatures etc. suitable for their spawning 

 and development. It appears further that the sea-bottom is less steep here off the Channel 

 so that a relatively large area arises with depths from 1000 — 2000 meters, i. e. the depths 

 over which the greatest numbers of eel larvae have hitherto been found. 



b. General remarks on the distribution of the eel larvae 



The larva of the European eel, Leptocephalus brevirostris , has thus been found 

 besides in the Mediterranean (Sicily and Naples) also in the eastern part of the Atlantic 

 over the tract, from the Faeroes to Brittany', but there is also every reason to believe 

 that it will be found in the whole of the eastern part of the Atlantic basin as far south 

 as the temperature in deep water will permit. 



Wherever the larva has been taken 2, it was found pelagically over or near the, 

 relative to the extent of the ocean, narrow slope which is somewhat parallel to the con- 

 tinental coast line. That it normally lives here cannot thus be doubted, otherwise why 

 should the discoveries hitherto made, concerning which sufficient information can be 

 gained, agree in this respect? 



That no eel larvae, except perhaps single drifted off specimens, are to be found in the 

 Northern Ocean, North Sea or Baltic, is quite beyond doubt. In the Northern Ocean the 

 Norwegians have made many investigations with the "Michael Sars", partly with Petersen's 

 young-flsh trawl, and extremely rich collections of pelagic fish young were the result, but 

 there was not a single Leptocephalus brevirostris taken by them. In the Danish waters 

 and part of the Baltic Dr. C. G. Joh. Petersen of the Danish Biological Station has been 

 making collections of pelagic fish young for about 20 years with the best existing appa- 



■ By the investigations of the "Thor" in May and June 1906 it has also been found so far south as 

 right off the North coast af Spain. (Note added during press.) 



2 The only two discoveries, in addition to the "Thor's", which throw some light on the normal occurrence 

 of the eel larvae are those of Lo BIANCO (Mediterranean) and HOLT (west of Ireland), As mentioned in the 

 Introduction Lo Bianco's specimen was taken near Capri on April 2nd igor over ca. 1000 meters. Holt's 

 specimen (according to the Department of Agriculture & Technical Instruction for Ireland, Fisheries Branch, 

 Biological Collections, List of Stations, Part I, 1899 — 1904, Dublin 1905, p. 82) was taken on Aug. nth, 

 1904 at Lat, 54°5o' N., Long. io°45' W., depth -^^ fathoms. This station lies close the tooo meters curve 

 as the sea-bottom here descends very steeply. 



