256 THE COMMERCIAL SEA FISHES OF 



waters ? Or must we conclude that they were absent fol- 

 lowing their food, which from some cause was not present 

 in its usual haunts ? The explanation offered by the Nor- 

 wegian Board of Fisheries appears to be that whether they 

 come to spawn off the coast depends upon the distance they 

 have to go in search of their summer food, while this in its 

 turn depends upon the variation in the direction of the 

 prevailing winds. 



The two main objects of migration would appear to be 

 seeking some locality where spawn may be safely de- 

 posited and the species continued ; or else a search for 

 food in order to maintain the growth and existence of the 

 individual. But it would seem that fish may seek new 

 ground, due to that they usually reside in becoming un- 

 suited from any cause, as absence of food, or even their 

 constant capture by incessant netting. If having selected 

 waters further from the shore than formerly, the spawn 

 were deposited and bred there, it does not seem unreason- 

 able to suppose that the progeny would locate themselves 

 where they were reared. In time, perhaps, this new loca- 

 tion might be found unsuited, and the shoal might return 

 to the spot they first inhabited, and where possibly a more 

 abundant supply of surface food exists. 



Respecting the effect of temperature and various meteoro- 

 logical conditions of the atmosphere as affecting migrations 

 and captures, so little has yet been ascertained on these 

 points that I think it better to refrain from speculating 

 upon them. Fishermen assert that prevalent winds are a 

 cause of migrations, and if so this is probably effected 

 through its acting on their food. Seasonal changes, how- 

 ever, doubtless have an effect in hastening or retarding the 

 advent of herrings ; while diurnal variations may likewise 

 be coincident with the bathymetrical depths at which they 



