762 



DEPTHS OF THE OCEAN 



Some of the general results obtained by these investigations 

 are of great interest ; for instance, the growth of fishes has 

 proved to be largely dependent on the temperature. Some 

 chemical investigations corroborate this. Fig. 556 shows the 

 fat-contents of the sprat as determined by H. Bull, compared 

 by Sund with the surface temperature of the sea off western 

 Norway in various seasons of the year. The fat-contents of 

 the sprat increase during summer, when there is a rise in temper- 

 ature, while both decrease towards the end of the year ; it 

 follows from this that the growth of the fish must be influenced 

 by the prevailing temperatures in different waters. 



The investigations on the scales of 



fishes have now given us numerous 



facts confirming and elucidating this. 



Thus Damas says that the age of first 



maturity in the cod undoubtedly varies 



greatly according to local conditions. 



Generally the growth of cod -species 



flliin'lllllliiiil^l^^J^^'^^fiiflilllllliiiij "^^y be said to decrease, and the age of 



pS'V#E|^^i^^^^^^ first maturity to increase, the farther 



te»;^^^^^ north we go. Thus on the Skagerrack 



\Um>^y>-^^W/o'.!,!iiliA ^^^3, ^ 3^i^j^^ ^^y be 30 cm. long at the 



end of its first year, while a saithe of 

 corresponding age in northern Norway 

 is not, as a rule, more than 10 cm. in 

 length. In northern waters, therefore, 

 the winter-rings in the scales are much 

 more marked than in more southern 

 waters, for instance, in the North Sea. 

 The duration of the warm season also 

 differs in different waters, and the time when it sets in 

 varies in different localities as well as at different depths (see 

 Fig- 509- which shows that at 200 or 300 metres the highest 

 temperatures do not occur in the summer, but late in the 

 autumn). An examination of cod scales from the Barents Sea 

 proved that in August summer growth had not yet commenced 

 in that area, where the winter season is of very long duration, 

 while the summer is short. It is interesting to compare this 

 with certain observations which we had the opportunity of 

 making during our Atlantic cruise on the banks of Newfound- 

 land, where, as mentioned on pp. 109- 114, the cod spawn in 

 July. We here observed cod with large ripe ovaries and found 

 the recently hatched larvae at the surface. The scales of these 



llSiiiiiiiii 



iil 







Fig. 557. 

 Scale of Gadus callarias, L. Nat. 

 size of fish, 55 cm. Station 72. 



