EGGS AND FEY OF THE HEEEING 159 



spawning season is said to be May to August ; off the east coast 

 of England, July to November. Off Plymouth, on the other 

 hand, herrings spawn in December and January. The mean 

 surface temperature of the w^aterin December in 1919-20 was : 



Dec. Jan. 



Off Plymouth Pier . . . 50-1° F. 47-4° F. 



Off Prawle Point . . . 51-8° F. 49-6° F. 



The Influence of Temperature 



It would be interesting to have a comparative table of the 

 surface and bottom temperature of the sea on all grounds on 

 which herring are known to spawn all round our islands for 

 the whole spawning period. If such a table has been prepared 

 it has never been made public in any popular form. The 

 Cardigan Bay herrings spawn in October and November with 

 water at about 55° F. to 52° F. (surface). Dutch investigators 

 maintain that herrings are most plentiful in water between 

 53-6° F. and 57-2° F., and all Dutch herring-boats carry ther- 

 mometers in order to enable them to fix their nets at the proper 

 level.^ 



Some years of observations at Wick with the deep-sea 

 thermometer showed that the best catches were made with 

 a day temperature of 55° F. falling to 54° F. at night, and that 

 a fall below 53° F. meant no fish at all. Boeck, in his report 

 to the Norwegian Government in 1862, made careful observa- 

 tions on temperatures. He found (after a spell of cold weather) 

 that the water at 10 fathoms was about 35° F. or 36° F. There 

 no fish were caught. But when the nets were lowered to 50 

 or 60 fathoms and a temperature of 39° F. to 41° F. the catch 

 was good. 



It was believed by Frank Buckland that herrings rise from 

 the bottom as temperature increases, and swim at a higher 

 level during the spawning season. Mr. 0. C. Morley, of Milford, 

 however, stated that his trawlers only caught herrings off Ireland 

 at 60 fathoms when the weather was ' very hot '. 



Develojyment of tJie Fry 



Herring larvae, when they hatch out, vary (according to the 

 * race ' they belong to) from 0*19 to 0'31 inch in length. They 

 absorb the yolk-sac very quickly, and remain at the bottom 

 during the process. During January and February this year 

 (1920) 1,032 young herrings, varying from 0-31 to 0-58 inch in 

 length, were caught off Plymouth. They were examined by 



^ Stacey Watson, Silver Hosts of the North Sea, p. 18. 



