CONSERVATION OF DEEP SEA BEDS. 1035 



temperature rather than by means. The extreme cold of 

 winter in the southern part of the North Sea, as contrasted 

 with the heat of summer, may explain why it is that fishes 

 that prefer moderately warm water, such as the mackerel 

 and pilchard, are not more plentiful there. We have seen 

 that the mean variation of surface temperature in East 

 Anglian waters is 20, but the extreme variation, especially 

 in seasons of exceptional severity, is considerably greater. 

 In winters of severe and protracted frost the fauna of the 

 intertidal zone suffers not a little ; and even oysters not 

 subject to exposure by the recession of the tide occasion- 

 ally perish in great numbers. Certain fishes are also 

 highly sensitive to cold. In times of biting north wind, 

 with very low temperature protracted for days, congers in 

 the genial waters of the south-west of England both 

 -North and South Devonshire have been found in shoals 

 floating helplessly numbed on the surface of the water. 

 Surface-swimming fishes at such times take refuge in com- 

 paratively deep water beyond the range of these meteoro- 

 logical fluctuations. In shallow water of less than twenty 

 fathoms the effects of storms would be considerable even 

 at the sea-floor, but in the deeper water of the " pits '' the 

 conditions would be much nearer those of a normal season. 



In deep water there is protection against extremes or 

 even serious changes of temperature, and also against the 

 fury of the gale. 



Low temperature has been supposed to retard the 

 spawning of fish. If, however, for the reasons connected 

 with surface food just indicated, the shoreward movement 

 is delayed, all that can be said with certainty is that the 

 spawning fish are not met with so early as usual. Food is 

 no doubt obtained in greater abundance when compressed 

 into a smaller thickness of water, and it is possible, of 



