4 B. B. PARRISH 



northern, central and southern regions of the North Sea, and whose distribu- 

 tion is bounded by the continental slope in the north and east. Only in the 

 'fringe' region of the northern North Sea has any substantial overlap in the 

 distributions of these tribes been detected in the forty to fifty years of intensive 

 herring research in this area. Therefore, for fishery assessment purposes, the 

 'Atlanto-Scandian' tribe can be discounted as a substantial source of supply 

 for the North Sea herring fishery, and as a factor governing the fluctuating 

 yields from it, and vice versa, at least during the present century. The 

 approximate boundaries between the two tribes and the region of overlap 

 between them are shown in Fig. i. 



Throughout their long histories, these two fisheries have been characterized 

 by marked long- and short-term fluctuations and trends in landings. The 

 most striking of these have been the 'herring periods' of the Norwegian 

 (and Swedish west coast) fishery; they have taken the form of alternate 

 periods of high and low yield, which can be traced in the Norwegian and 

 Swedish statistical records, back to at least the sixteenth century. The most 

 recent 'low' in the Norwegian fishery occurred towards the end of the 

 nineteenth century, when, between i860 and 1875, the annual landings fell 

 from about one milhon hectolitres to 200 hectolitres. An equally large and 

 rapid rise took place early in the twentieth century, and by 191 3 the annual 

 yield had risen again to over a milhon hectoHtres. 



Marked fluctuations are also reflected in the early and later catch records 

 of the North Sea, and neighbouring herring fisheries. In some notable 

 instances (e.g. Firth of Forth; western Enghsh Channel) these have been of 

 sufficient magnitude, and the period of low yield sufficiently sustained to 

 cause the complete collapse of a traditional fishery, while in others they 

 have resulted in sharp changes in the 'success' of the fisheries. 



This 'property' of the European herring fisheries had a marked and lasting 

 influence on the attitude of early and later herring scientists to the relative 

 importance of natural and man-made factors in governing the yield from 

 them. Man-made influences (i.e. fishing) tended to be regarded as of 

 relatively small importance. This attitude persisted during the period of 

 decline of many of the important demersal fisheries, and the rapid growth 

 of quantitative studies of the dynamics of the exploited demersal stocks in 

 the inter-war and early post-war years. Throughout this period the European 

 herring stocks were generally regarded as underfished, but subject to wide 

 natural fluctuations in abundance, distribution and habits. As a consequence, 

 the kind of scientific data collected on the herring fisheries remained largely 

 qualitative in nature. 



Since the second world war, however, disturbing events in some com- 

 ponents of the North Sea fishery have caused an urgent reappraisal to be 



