444 



DEPTHS OF THE OCEAN 



Influence of 

 temperature 



fishes. 



The northern forms — cod, haddock, saithe, flounder, and 

 hahbut — disappear along the coast of the southern states, as does 

 also the hake. On the other hand mullet, ScisenidEe, and 

 Sparidae, i.e. the southern forms, increase as we go south, just as 

 they do on the eastern side from the Bay of Biscay towards the 

 coast of Morocco. 



If, with these facts in mind, we look at the chart (Fig. 312) 

 ,.,. recording: the temperature at a depth of 100 metres (about 50 



conditions on p ,11, -ii 1 r 1 1 tm • 



distribution of fathoms), we shall be astonished at the tact that the distribution 

 of different species curiously coincides with certain temperatures. 

 The southern limit of northern boreal species everywhere 

 coincides with the isotherm for lo^ C. On the west side this 

 isotherm just reaches the border between the northern and 

 middle states of North America, while on the east side, on the 

 coast of Ireland, this isotherm just separates the two areas 

 termed respectively areas north-west and south-west of the 

 British Islands. 



The areas of the northern species correspond on both sides 

 of the ocean to the area between 2° and 10" C, the maximum 

 frequency of the species occurring between 6^ and 8° C. These 

 latter temperatures are found on the Newfoundland banks, on 

 the southern and western banks of Iceland, in the North Sea, 

 and along the entire coast of Norway. The uniformity of the 

 fauna peculiar to all these localities compares well with the 

 uniform conditions of temperature. South of the 10° isotherm 

 we have on both sides of the ocean belts with temperatures 

 between 10' and 18° C. ; that on the west side ranges from 

 Cape Cod to Florida, and that on the east side from Iceland to 

 south of the Canaries. 



A peculiar feature is that all the isotherms on the west side 

 are quite close together, the water layers being squeezed 



