Aberdeen Fishery Statisties. 15 
But by far the most important lessons of a practical kind that may 
be drawn from these statistics are such as come from a comparison, 
year by year, and month by month, of the results of the fishing on 
individual areas, that is to say, of the average catches of this or that 
particular fish. And so I shall proceed to consider the full Tables 
of Averages set forth on pp. 32-61, which (as has been said) are 
drawn from 8225 voyages during the year 1912. Herein lies the 
one sound and satisfactory method of approaching the problem of 
whether the available stock shows signs of diminution or not. As 
has been repeatedly set forth in former Reports, the problem is not 
a simple one, but has to be set and answered afresh for each species 
of fish, and considered in detail for various regions or areas. For 
its proper understanding, also, it requires more or less copious illus- 
trations by means of diagrams or curves. 
It is neither requisite that this question should be fully discussed 
at frequent intervals, nor is it possible that I should make use at 
any one moment of the whole mass of the Board’s accumulating 
statistics. I propose, rather, to take each year one or two particular 
fishes, and to supplement the statistical tables with figures illustrating 
the fluctuations in abundance of these, during the whole period for 
which information is available. It will be necessary to limit these 
illustrations to a few of those areas for which the Board’s information 
is most abundant and continuous. 
Let us, then, on the present occasion, look briefly at the catch of 
cod and codling, of ling, and of the witch, during the past eleven or 
twelve years, on the important areas XXIII. (off the Aberdeen 
coast), XXIX., immediately to the southward thereof, X. (the Shet- 
land area), XIV., to the southward of Shetland, and including Fair 
Isle Bank, and XVITI., which includes the Pentland Firth and the 
sea to the westward of the closed waters of the Moray Firth. We 
may add to these the North-Western area C, whose principal fishing- 
grounds are in the neighbourhood of Rona and Sule Skerry. 
The curves are so simple that a few words of explanation will 
suffice. On each is shown, month by month, the average number 
of cwts. landed per 100-hours’ fishing by the vessels from which 
information has been received; and the points corresponding to 
these monthly catches are found to run together in a continuous and 
more or less simple curve. The points upon this curve, as has been 
repeatedly explained, have been subjected to a slight process of 
smoothing, which consists in replacing the actual observed average 
for each month by the mean between it and the adjacent averages 
for the month before and the month after. In short, each point 
represents the average catch during three months instead of during 
cne. With no impairment of the statistical value of the data, this 
gives a smoother and simpler curve, by eliminating a number of 
minor and accidental fluctuations. 
It may be observed, in the next place, that every one of these 
continuous curves represents, more or less clearly, a succession of 
waves, one in each year; and the nature of this annual periodic wave 
may be ascertained by adding together and averaging the monthly 
values for the whole term of years. 
Thus, in the curves (figs. 5, 11) which illustrate the average catch 
of cod and codling in Area X. (Shetland), it is seen at once that the 
