39 



of the most northerly and westerly shoals can be possible only if 

 there is a compensatory contranatant* migration. 



The 3^oimg herring shortly after birth and when the yolk sac 

 has been absorbed, frequents mid -water where it has been taken 

 towards the end of March and in April. About the end of June, 

 after a short sojourn near the surface, migration commences 

 towards the shore. Young from autumn spawners spend less 

 time in the mid -water and the latest of them appear to migrate 

 shorewards without an intermediate journey through the mid- 

 water to the surf ace. t There is therefore a period of about three 

 months for the young arising from* spring spawners, and a shorter 

 period for the young from autumn spawners, during which they 

 8.re subject to the influence of currents. 



The extent of denatation possible can be appreciated only 

 b}^ a consideration of Fulton's experiments. J A drift of from 

 2 to 6 miles per day was found to be common. If the currents 

 of the mid-water are a,pproximately the same as those of the 

 surface the young herring may be carried some hundreds of 

 miles from its place of birth. It is not intended here to give 

 detailed examples of the amount of drift observed, but the following 

 may be of interest as indicating the possibilities of denatation 

 in our local waters. One of the bottles liberated near the mouth 

 of the Firth of Forth, 2()th March, was found on the Northumber- 

 land coast, having drifted 82 miles south in fifteen days.[l 



The post larval stages originating from the more northerly 

 shoals will be drifted south along the east coast of Scotland, which 

 will receive also the x^roducts of the spawning shoals of the north 

 coast of Sutherland, and possibh^ some of the j^oung from the 

 north of Lewis. 



Once the 3^oung fish come under the influence of the tidal 

 stream running between the Orkney Islands and in the Pentland 

 Firth, which attains a speed varying from 2 to 8 miles per hour, 

 they will be carried quickly into the North Sea, where they will 

 eventuaity form summer feeding shoals of young fish. It has been 

 shown that these summer feeding shoals give additions to the 



* Professor Meek, op. cit. 



t Mcintosh and .Masternian. British Marine Food Fishes. 



J Tlie Currents of the North Sea and their Relation to Fisheries. 15th Ann. Kept. Fish 

 Bd. Scot. 



Il Fulton, op. cit,, p. 348, 



