— i6o — 



long hauls (of 2 hours duration) were made with the large young-fish trawl'. The highest 

 number we obtained at these stations was 3 specimens per 2 hours haul. 



We had thus succeeded according to expectation in finding the larvae of the eel to 

 the west of Scotland in the deep warm Atlantic water. Nevertheless, the numbers found 

 appeared to me too small to let us conclude that we were over the spawning places of 

 the great mass of the North European eels, even though we had by no means hoped to 

 discover the eel larvae in such large quantities (hundreds or thousands per haul) as we had 

 found the pelagic young of other food-fishes, e.g. cod {Gadus callarias) or haddock 

 {Gadus aeglefiniis). In contrast to the eel these last collect just at spawning time on 

 shallow banks of relatively small extent, and the water masses of relatively small 

 depths in which the pelagic young later appear are consequently much more densely 

 populated by these young than could be expected to be the case if the spawning had 

 occurred in deep water. That the pelagic young of species which spawn in deep water 

 are much more scattered in the water-masses was well-known to me from the investiga- 

 tions of earlier years, as e. g. the young of the halibut {HippoglossHS vulgaris), which 

 was found indeed over about the same depths as the eel larvae. We had been able 

 however to take as many as 10 young of the halibut in a 30 minutes haul with the 

 smaller model of the young-fish trawl, and it appeared to me probable therefore that we 

 ought to obtain quite as many of the eel larvae, especially as we were making longer 

 hauls with a larger apparatus 2. 



It is mentioned above that the plan for the investigations was to seek for the eel 

 larvae in the deep Atlantic water to the west of Scotland, our working hypothesis being 

 that the eels which migrate out to their spawning grounds from the Baltic and North Sea 

 pass out to the Atlantic for the most part through the passage to the north of Scotland. 

 It appeared however that the larvae were only in small quantities to the west of Scotland. 



For this reason I concluded that the investigations on the occurrence of the Lep- 

 tocephali could not be brought to an end until we had also endeavoured to determine 

 whether they did not possibly occur in greater numbers off the English Channel to the 

 S. W. of Ireland. There was indeed nothing to hinder the greater part of the North 

 European eels from migrating out through the Channel to spawn and in addition to this, 

 I had taken a pelagic elver in April 1905 on the Dogger Bank in the southern North Sea 

 which was clearly by way of migrating in towards the coast, and which from the position 

 of the place where it was taken might equally well or even preferably be considered to 

 have come into the North Sea from the Atlantic through the Channel as round Scotland. 



' The measuiements for the two models of young-fish trawl are as follows: 



(Length: 7-20 meters 

 Small trawl ^ Circumference at opening; 7 '20 meters 



\ „ „ narrow end: 3*05 meters 



/Length: 976 meters 

 Large trawl J Circumference at opening: i2'2o meters 



I „ „ narrow end: y66 meters 



2) It may be remarked incidentally however that we can by no means conclude beforehand that a long 

 haul with the young-fish trawl will give the same quantity of pelagic fish young as several shorter hauls of 

 altogether the same duration ; for the reasons, on the one hand, that the fish young are not as a rule quite 

 evenly distributed, on the other that the apparatus if out for a long period often takes in quantities of jelly- 

 fish, Salpidae, diatoms etc. which affect its capacity of filtering water and thus of fishing. 



