78 
QO. Pettersson in a paper * Tong Periodical Variations of the 
Tide Generating Force’ * has shown that the moon and sun 
have considerable influence on the waters of the earth, and that, 
the tide generating force varies through a nine-year period. This 
tide generating force which produces activity in Atlantic waters 
was at its highest at intervals of nine years from and before 1903.7 
It coincides with year number 8 in this paper, and is followed by 
an interval of four years by the increased catches of year number 3. 
This is taken as indicating that the activity of Atlantic waters 
has an effect on the production of a good year-class, and together 
with the fact that herrings with three winter rings have been 
found to be of such great importance in the fishery, it gives support 
to the working hypothesis that the conditions preceding the year 
of spawning are of greatest importance in determining a good 
year-class. 
The difference between the cast and west coast fisheries for 
years number 6 to 8 is taken as indicating the possibility of northern 
waters having some effect on the east coast fishery by bringing 
about variations in the flow of Atlantic water into the North Sea. 
In this connexion it is of interest to recall the following statement 
by Matthews.t “It may be accepted as an axiom that for the 
purpose of fishery investigations it is not so much the mean hydro- 
graphic conditions as the deviations from this mean which are 
of primary importance, and this holds with special force in the areas 
of which the fish fauna is fairly well-known.” An abnormal inflow 
of northern waters into the northern North Sea does not appear 
of itself to be sufficient to produce a good year-class, for the year 
1908, when cold water reached as far south as Aberdeen,§ was not 
followed by any indications of a year-class worthy of note in the 
herring fishery of the East Coast of Scotland. The best herring 
season since 1907 was that of 1910, and after that the catches 
gradually decreased. The 1910 catches were due probably to the 
extensive salt water inflow stated by Robertson!) to have taken 
place into the North Sea throughout the winter of 1905-6, and 

* Pub. de Circ., No. 65. 
+O. Pettersson. “ Climatic variations in historic and prehistoric times.’ 
t Report on the Physical Conditions in the English Channel and Adjacent Waters, 1906, 
page 271. North Sea Fish. Invest. Committee, 3rd Report, Southern Area, Cd. 5546. 
§ Robertson. Report on Hydrographic Investigations in the North Sca and Faroc- 
Shetland Channel during the years 1907-1908. North Sea Fish Invest. Committee, 4th Report, 
Northern Area, Cd. 4893. 
|| Op, cit., pp. 163-164. 
> 
