— 128 — 



we compare with this what has been shown in this paper with regard to the spawning of 

 the gadoids in these different waters, we find what beforehand might seem very remarkable, 

 that S. Iceland and S. Ireland resemble one another more in spite of the 

 great distance between them than the two waters S. and E. of Iceland which 

 are quite near to one another. If indeed we take the eastern part of south Iceland 

 as starting-point and go from there towards the east coast, we find before 50 miles have 

 been passed that the conditions with regard to the production of the gadoid fry have 

 changed more completely and more strikingly than if we had set out from the same 

 starting-point and sailed over the long distance of ca. 700 miles to South Ireland. A 

 more remarkable proof of the importance of the hydrographical conditions can scarcely 

 be imagined. 



4. North Sea 



As the North Sea does not really belong to my region but will be dealt with in 

 detail by Dr. Damas in the present report, I shall only discuss here some points of impor- 

 tance for a general view over the reproduction of our Atlantic gadoids. I may first of all 

 remark that such a large area as the North Sea with its small depths and thus suited to 

 the occurrence of the majority of the gadoids is unique amongst European waters. As there 

 is likewise great variations in the temperature and salinity both in the different parts of 

 the North Sea and at different times of the year, this region is of great importance for 

 the investigation of the influence of outer factors on the spawning of the gadoids. The 

 influence of the salinity is especially distinct here, where the isohalines which are of 

 importance for us are much wider apart than is the case on the Atlantic coasts, a condi- 

 tion which naturally greatly facilitates a judgment of the importance of the salinity. As 

 a characteristic feature of the North Sea the small depths should be noticed first of all, 

 as several of our species are therewith excluded from spawning here. Further the great 

 variations in the temperature in the course of the year must be emphasized, especially in 

 contrast to the conditions in Atlantic waters. These variations are specially conspicuous 

 in the shallow eastern and south-eastern parts of the North Sea (also in the neighbour- 

 hood of the English coast), that is, in the parts which are furthest from the Atlantic 

 waters; and it can be seen from all the surface charts for February and August in the 

 International Bulletins, that these variations here amount to more than 10°, and for the 

 coastal belt even as much as ca. 14° — 15°. In contrast to these the temperatures in the 

 north-western part of the North Sea are much more "Atlantic" in their character, i. e. 

 more uniform throughout the year. 



It may be said in general that the surface temperatures decrease as we go from the 

 north-western parts of the North Sea towards the east or south-east in the spring, whereas 

 in the summer the opposite is the case. 



The conditions in the North Sea in February— March 1906 (thus at a season when 

 several of the principal gadoids are spawning) can be seen from figs. 9 and 10, which 

 represent the principal hydrographical conditions at the surface and bottom. We see at 

 once from these that the lowest temperatures and salinities occur in the eastern and 

 south-eastern parts, where the 4° isotherm and 34" loo isohaline of the surface waters pass 

 to some extent parallel to the continental coast line at a greater or less distance from it, 

 whilst a large tongue of Atlantic water with salinity of 35'0 — 35-2 "/oo or over 35-2''/oo 



