544 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. [20] 



which the saltuess decreases and the warmth increases, and pursue their 

 course until they finally meet at the time when the spawn and milt are 

 fully matured, in places which resemble their own birth-places. 



As soon as the sexual organs have been emptied, the desire which led 

 the herrings of both sexes to the spawning-places dies out. The large 

 schools do not permanently find sufficient food in these confined waters. 

 The desire for food therefore compels them to scatter again. Swimming 

 hither and thither in search of food, they find more towards the open 

 sea than in the direction of the coast, because most of the small marine 

 animals (crustaceans, &c.) on which the herrings feed could increase 

 and develop more undisturbedly in the open sea, as long as the whole 

 host of their inveterate enemies (the herrings) staid in the bays. 



Not only old, fully-grown herrings, but also the young ones migrate. 

 From the Schlei many young herrings, measuring only 60 to 70 milli- 

 meters, go to the Baltic in August. 



The migration of the herrings from the open sea into the bays and 

 back again to the open sea is a means, employed by nature in order to 

 raise large numbers of fish; for because the herrings wander, they 

 always have plenty of food; and their migrations are generally brought 

 about by the fact that they continue to swim in that direction where 

 they find the most food. 



"When the herrings come from the open sea into our bays, and are 

 caught, they furnish us with healthy food which has been formed by 

 small marine animals, which, without the herrings, would be of no use 

 whatever to us. 



In the Western Baltic there are two seasons of the year when herrings 

 spawn, namely, spring and autumn. 



In the Schlei most herrings spawn in April and May, and but few of 

 them in March and June. 



In the Kattegat the herrings likewise spawn in March, April, and 

 May, whilst on the west coast of Norway they spawn as early as Feb- 

 ruary and March. 



The herrings which spawn in autumn are not the same which have 

 spawned in spring. 



Autumn spawn is ejected by the herrings in the western and eastern 

 parts of the Baltic from September to November. 



The herrings which reach their maturity in autumn spawn in deeper 

 waters than those which spawn in spring. As in autumn the water is 

 warmer in the deep places than near the surface, it is probable that the 

 fully matured herrings which spawn in autumn are, just like those which 

 spawn in spring, compelled to congregate in deeper waters by tbe differ- 

 ence of temperature in the different depths of water. 



In the western part of the Baltic the saltness of the water increases 

 the deeper we go. The autumn spawn, therefore, is developed in much 

 salter water than the spring spawn which has been deposited in shallow 



