79 
brought about by the abnormal conditions existing in the Northern 
Atlantic. 
The Yarmouth fishery differs from that of the east coast 
of Scotland and also from that part of the west coast fishery which 
has been sampled from Stornoway. ‘The Yarmouth shoals consist 
of older herrings, and it is possible that other factors may bring 
about the increased catches of years number 7 to 9. In these 
years the tide generating force is at its highest, and Atlantic water 
reaches its greatest activity. It has been shown by Pettersson* 
that the herring fishery of the Baltic has fluctuated with the 
activity of Atlantic water as influenced by the position of the moon. 
The herrings penetrate into the Baltic according to the inflow 
of Atlantic water, and it is possible that large inflows of water 
of high salinity would drive or carry the herrings into the southern 
waters of the North Sea and be the chief cause of big catches, pro- 
vided always the herring population was large enough for the 
purpose. 
The increased catching power of fishing vessels has been 
referred to. This makes the reading of the Yarmouth data more 
difficult, especially for the years 1904 to 1913. From the catches 
made during the periods 1878 to 1886 and 1887 to 1895 it would 
appear that migrations, if migrations be the cause of the large 
catches in years number 7 to 9, are not so great during each period, 
and that the greatest movements of fish into the southern North 
Sea are separated by a period of eighteen years. 
A periodicity in migrations is suggested by the catches of winter 
herrings on the east coast of Scotland. For a number of years 
the catches from the winter fishery were small, and then came 
an increase. The maximum catches were made in the years 1902 
to 1905, and since then there has been a general tendency to 
lower catches. This is shown by the fellowing data supplied by 
the Fishery Board for Scotland. 
Year. Cwts. Year Cwts. 
1896 we 70,499 1905 nod 237,579 
1897 sae 65,853 1906 ne 190,551 
1898 ata 75,009 1907 aes 224,880 
1899 wag 112,174 1908 ares 170,065 
1900 me 190,875 1909 cae 65,681 
1901 oe 177,281 1910 ops 82,109 
1902 aes 276,682 19i1 sae 78,509 
1903 eas 220.799 1912 ASS 38,150 
1904 éce 276,195 1913 20 96,118 

* Climatic variations in historic and prehistoric times. 
