— 9 — JOH. HJORT AND C. G. JOH. PETERSEN 



The smaller the depth the greater are the changes in the physical conditions and the 

 more varied is the animal life. Whilst it may seem right to regard the vast area of the sea- 

 bottom which lies between 200 and 600 m. as one single characteristic region, neither from the 

 point of view of the natural history of the fishes nor from the study of the actual fisheries, 

 can we consider the above-mentioned banks, whose depths are all less than 200 m, as a group 

 of regions similar to one another; we find everywhere so different physical conditions, so 

 different animals and fisheries, in the various depths from the beach to the 200 m. line, 

 that we must seek to form still narrower districts. 



It may be said in general, that 3 regions can be distinguished «on all the known banks. 



The first region embraces depths from 60 — 200m, and is characterised chiefly by the 

 following fishes: 



Flat-fishes: witch (Pleuronectes cynoglossus), long-rough dab (Drepanopsetta platessoides), 

 megrim (Zeugopterus megastoma), as well as younger (smaller) specimens of the 

 halibut (Hippoglossus vulgaris). 



Eound-fishes: haddock (Gadus aeglefinus), cod (Gradus callarias), green cod (Gadus virens), 

 whiting (Gadus merlangus). 



For the fishery, the witch amongst the flat-fishes and the haddock amongst the round- 

 fishes have by far the greatest importance. It is characteristic that the plaice, the lemon sole 

 and the dab are absent or occur but sparingly. It is of general biological interest further, that 

 we find the young of the fishes which inhabit the slope of the coastal banks in this region, e. g. 

 small and medium-sized specimens of the ling, tusk, catfish, Norway haddock, great silver 

 smelt and halibut in quantities, and it is only the younger stages of these fishes which 

 chiefly occur in this region. 



The second region embraces the depths from 20 — 60m. It is chiefly characterised 

 by the flat-flshes (plaice, dabs, lemon soles, young specimens of halibut, e. g. of 20 — 40 cm. in 

 length) and the younger stages of haddock, whiting and cod. The witch is absent, the ling, 

 tusk and the larger haddock occur only sparingly. In this region are the spawning grounds of 

 the cod and haddock. 



The third, the littoral region from the beach to a depth of 20m, is above all the 

 region of the young of most of the useful species, namely, plaice, dabs, cod and haddock 

 during their first year. 



For the better understanding of the physical relations of these three regions, we shall 

 consider more closely the largest and most important of the banks mentioned here, namely the 

 North Sea banks (see Table 11 and III). 



As a rule, this is considered as inclining uniformly from the German Bight down 

 towards the northern slope. A closer examination of the bottom of the Nortli Sea bank shows 

 however, that the actual conditions are essentially diflerent, as a series of irregular depressions 

 and slopes occur here. 



Along the east coast of Scotland and north of England, the 40 — 50 m. lines run parallel and 

 very near to the coasts. From Flamborough Head, the 60 m. line bends strongly from the coast 

 towards Hanstholm on the Jutland coast. Thus, the North Sea bank is divided by the 60 m. line 



Appendix Or 2 



