THE SALT-WATER FISHERIES OF BOHUSLAN. 173 



rhe earth, bj^ a change in the direction of the currents of the sea, and 

 especially of the Gulf stream, or by the influence of the polar ice and 

 its floating to"wards southern regions, &c. If future scientific investi- 

 gations should prove the existence of such a periodicity, it is quite 

 probable that light will be thrown on many a dark point in the biology 

 of the herring. 



20. Among the hydrological phenomena which for the better under- 

 standing of the mode of life and the migrations of the herring require 

 our attention, the more or less agitated condition of the water caused by 

 the winds is the most prominent. The motion of the waves seems to 

 exercise an influence on the herrings partly by aerating the water, 

 partly by mixing water of different temperature, and finally by the 

 occasionally very violent agitation which is produced even in the lower 

 regions of the water near the bottom. The last-mentioned effect of the 

 motion of the waves, which shall form the subject of special investiga- 

 tions, has a considerable influence especially on the spawning herrings, 

 which need calm waters for spawning, heavy waves often compelling 

 them to seek spawning-x)laces which are sheltered or in the deep water 

 where the motion of the waves is not so perceptible. Gisler says that 

 violent storms tend to weaken the herrings when near the coast, and 

 numerous observations corroborate the fact that during such storms 

 the herrings leave the coast or seek sheltered places ; and even the 

 heaving of the sea preceding and indicating the approach of a storm 

 seems often to have the same effect. The direction in which this heav- 

 ing takes place forms, therefore, one of the more important signs, from 

 which the fishermen predict the future of the weather and of the fish- 

 eries. In the open sea, far from the coast, the motion of the waves 

 seems to have no or little influence on the herrings; the Dutch so-caUed 

 ' ' large " herring-fisheries are therefore not at all influenced by it. Smaller 

 surface waves seem always to have a favorable influence on the fisher- 

 ies, probably because they break and therefore subdue the light. 



21. We must also take into consideration the different height of the 

 water which is caused by wind and tide. On coasts where the tide is 

 very perceptible, it doubtless exercises a very considerable influence, 

 especially on the fisheries, — much more so than on the life of the herring. 

 Ferley says that in the Bay of Fundy, during the spring tide, in early 

 summer, herrings which have come to the coast to seek food are easily 

 caught even during day-time ; and at Yarmouth the richest hauls are 

 made when the tide comes in during the three hours before and the 

 three hours after midnight. According to Strom all kind of fishing is 

 more successful at Sondmcir when the tide is in than when it is out. I 

 have been informed that on the west coast of Scotland the herrings are 

 nearer the surface during slack tides than when the tide is high. On the 

 coast of Bohuslan the tide is not very perceptible during the season 

 when the principal herring-fisheries are going on; and this whole matter 

 has been studied so little that not much can be said regarding the influ- 

 ence which the tide has on the herrings. 



