296 FISHES 



departs again to the south in winter, these shallow waters of the 

 coast of Holland being warmer in summer than the Channel. The 

 pilchard approaches the coast of Cornwall, which is the northern 

 limit of its range, in summer and autumn from July to Christ- 

 mas, and retires to the south in the colder months ; its object is 

 food not reproduction, for it is known to spawn from twenty to 

 fifty miles from the land and those which are caught near the 

 coast have the reproductive organs undeveloped. A curious 

 fact about the pilchard is that the young fish which are caught 

 on the coasts of France, Spain, and Portugal, and preserved as 

 sardines, are not usually found in large numbers on the Cornish 

 coast, only the adults travelling so far north. These are ex- 

 amples of southern species which shed pelagic eggs and have no 

 special spawning places, but in their search for food follow the 

 summer to the northward ; similarly northern species extend 

 their range more to the southward in winter. In the case of 

 the herring, which is a northern species, the chief migration is 

 for the purpose of spawning and the movements cannot be 

 directly correlated with temperature ; the spawn of herrings is 

 adhesive and demersal, and is deposited on stony banks at 

 moderate depths near the coast. Any given ground is visited 

 annually, but the season for each ground is different, and there 

 is scarcely any month in the year in which spawning is not 

 taking place off some part of the British coasts. A broad di- 

 vision can be made between herrings which spawn in winter 

 nearer to shore and those which spawn in summer in deeper 

 water. Thus off the east coast of Scotland the spawning season 

 which marks the end of the summer fishing season is the month 

 of August, the warmest part of the year, while on the north 

 coast of Cornwall spawning takes place in the coldest month, 

 namely January. The winter herring at various stages of 

 growth enter estuaries in large numbers, for example the Forth, 

 the Thames and the Tamar. The movements of herring be- 

 tween the spawning seasons are not very completely known 

 but there is good reason to believe that thay do not go very far 

 from the coast, and it is probable that they congregate in shoals 

 at the spawning season more than at other times. 



The most definite and extraordinary migrations are those 

 undertaken by marine species which ascend rivers to deposit 

 their spawn or those fresh-water forms which descend to the 



