yob 



NA TURE 



[November 25, 1922 



herrings and, although small numbers of spawning fish 

 and spents are caught, the bulk of the catches consists 

 of fish which will become spring spawners. The her- 

 rings are of all ages, from fish with three winter rings to 

 those with as many as nine or ten, and the samples 

 obtained from these shoals point to the older fish being 

 the latest migrants. 



The herring fishery of the southern part of the North 

 Sea differs from that of the east coast in that it depends 

 for its success upon the presence of older and adult fish. 

 In this respect it is like the fishery in northern waters 

 about the Shetlands. But both these fisheries must 

 receive additions from the summer shoals of developing 

 fish if they are to continue in existence, and the 

 question of their productivity cannot be considered 

 without reference to the younger shoals. 



For other waters we have not the same quantity of 

 data as we have for the North Sea. In the Minch and 

 off the north-west of Ireland there are spring and 

 autumn spawners and summer shoals of developing fish. 

 In the Irish Sea the summer feeding shoals are followed 

 by autumn spawners, but for these waters, owing to the 

 large numbers of herrings with two winter rings found 

 in the catches of 192 1, further investigations are 

 required before a definite statement can be made as to 

 the age when the young fish join commercial shoals in 

 greatest numbers. 



The poor summer fishery of 1920 and its failure in 

 1921 can be accounted for by a shortage of fish with 

 three winter rings and belonging to the year-classes of 

 1917 and 1918. For an explanation of the poor catches 

 from shoals of adult herrings a consideration of their 

 age composition is necessary. Samples examined in 

 1919, 1920, 1921, and the spring of 1922, and obtained 

 not only from the East Anglian shoals but from the 

 north-west of Ireland and the north of Scotland, have 

 contained large numbers of fish of the 1913 and 1914 

 year-classes. In all samples the year-class of 1915 

 has been poorly represented. The year-class of 1916, 

 which gave the fairly successful summer fishery of 1919 

 when the young fish had then three winter rings, can 

 be considered a good but not a rich year-class. The 

 older herrings have naturally decreased in numbers and 

 the samples and catches obtained from shoals of adult 

 fish give no indication that a rich year-class of young 

 herrings has joined these shoals. 



While a consideration of the age composition of the 

 shoals leads to the conclusion that the failure of the 

 fishery is due to the relative value of the different year- 

 classes it indicates also that the migrations have had 

 some effect. Although we know little about the migra- 

 tions of the herring, there appears to be no doubt that 

 the migrations of the fish which have become adult and 

 joined spawning shoals differ from those of the young 

 which have not yet spawned. In the spring of 1921 

 comparatively large numbers of young herrings with 

 three growth areas on the scales were found as full fish 

 among the samples from the north of Scotland and 

 the Firth of Forth. Further sampling in 1922 has con- 

 firmed the finding of the previous year. Now, fish of 

 this age in the spring of the year are those which, in 

 June, July, and August, determine the yield from the 

 summer fishery. Since large numbers of them had 

 spawned in the spring of 1921, and afterwards would 

 migrate as adult fish, the summer fishery of that year 



NO. 2769, VOL. I IO] 



was poorer by reason of their absence. The high catches 

 made this year from the waters about the Shetlands 

 came, in part, from grounds which have been unpro- 

 ductive for a number of years, and they point to 

 migrations w r hich we know have followed the activitv of 

 Atlantic waters and herrings reaching maturity at an 

 early age. 



The age composition of the adult shoals fished off the 

 north-west of Ireland, the north of Scotland, and in the 

 southern North Sea, does not permit of the idea that 

 the conditions which govern the fishery occur in small 

 areas only. A consideration of the 1904 year-class from 

 data accumulated by Hjort and Lea gives some idea 

 of the widespread nature of the factors which produce 

 good year-classes. In the southern waters of the Gulf 

 of St. Lawrence the year-class of 1903 was found to 

 predominate, and that of 1904 in the northern waters 

 of the Gulf. The same year-class was the mainstay of 

 the Norwegian fishery for a number of years and was 

 rich in Icelandic waters. The large catches on the east 

 coast of Scotland in 1907 can be referred to the 1904 

 year-class, and so can the good fisheries of the English 

 Channel in 1909 and 1910. The conditions producing 

 good year-classes extend over the greater part of the 

 North Atlantic area. The difference between the north- 

 west of Ireland fishery and that of the North Sea in 

 1909 and 1910 suggests that in some years, e.g. 1905, 

 the factors which govern year-classes may move along 

 the west coast of Ireland towards the North Sea. The 

 age composition of the shoals in 1919-1921 indicates the 

 coincidence of conditions over the area north-west of 

 Ireland north into the North Sea. That variations in 

 oceanic circulation may bring about local changes in 

 the fishery would appear from the failure of the Firth of 

 Clyde fishery, 1904-1920, and that of the west of the 

 Shetlands, 1905-1922. The disappearance of young 

 herrings from the Wash points to the same conclusion. 



To say that fluctuations in the herring fishery have 

 been observed since the beginning of the fishery is to 

 make a statement incapable of proof but one which is 

 extremely probable. The history of the fishery, so far 

 as we know it, consists of a series of fluctuations, and the 

 attempts to account for these have given rise to ex- 

 planations which have varied from the conditions of the 

 year of capture to the wickedness of the people. 



However ridiculous some of these old opinions may 

 appear, it is only since Norwegian investigators, Hjort, 

 Dahl, and Lea, directed attention to the scales of the 

 herring that we have had any definite knowledge of the 

 age composition of some of the herring shoals. Few 

 people think of herrings in their fourth year as being of 

 greatest importance in our summer shoals ; a still 

 smaller number think of the conditions of the year of 

 hatching as being the factor which determines good and 

 poor year-classes. Evidence recently examined points 

 to this view requiring some modification and to the 

 possibility that the conditions of the year preceding 

 hatching are the dominant factor in the production 

 of good year-classes. Whatever modification may be 

 needed for this latest idea will depend on the knowledge 

 we hope will be obtained of the life of the herring before 

 it enters the commercial shoals. 



That the conditions preceding hatching are of greatest 

 importance is indicated by some of the results obtained 

 when this has been taken as a working hypothesis and 



