THE HERRING FAMILY. 



421 



The rate of growth, according to this table, agrees closely 

 with a mean increase of 4-5 mm. per month. 



The mean growth of the autumn-herring works out as 

 follows : — 



1 Month 

 2 



3 „ 



4 „ 



5 „ 



6 „ 



7 „ 



The early stages, in the winter-months, give a comparatively 

 slow rate of growth (3-4 mm.), but the length of the one-year- 

 old autumn-herring is approximately equivalent to that of the 

 spring-fish. 



The largest specimen in the St Andrews collection is one of 

 134 mm., which, according to the table, would be about 27-^ 

 months old and belong to the autumn-brood. 



As regards the migrations of the herring, the same theories 

 as in the case of the mackerel (see Mackerel) have been held. 

 Some have supposed that shoals of herrings migrated from the 

 Polar seas southward every year, and others have suggested 

 that myriads of herrings take an annual excursion round the 

 coast of the British Isles. It is probable that the migrations 

 are greatly localised,' and that apart from an annual migration 

 inshore connected with the function of spawning there are 

 lesser migrations of the shoals in quest of food. A pelagic 

 fish of gregarious habits like the herring must of necessity be 

 more or less itinerant, in order to satisfy the demands of 

 hunger. This species appears to live mainly upon minute 

 crustaceans and larval sand-eels, etc. which make up what is 

 known as the pelagic fauna, and the movements of these, 

 mainly- controlled by changes of temperature and weather, 

 probably determine the lesser migrations of the shoals of 

 herrings. During the breeding season the function of alimen- 

 tation is largely in abeyance, which enables the ' shoaling ' to 

 take place to a greater extent than would otherwise be possible. 



