SERA-FISHERIES LABORATORY. 139 
The lengths of the horizontal columns represent the 
variations in the percentages of the plaice caught of 16 to 17, 
17 to 18, 18 to 19 centimetres in length, and so on, We see 
that the majority of the fish caught le between about 17 to 
20 centimetres in length. It is easy to find what is the shortest 
range of lengths (say 17 to 21) which includes just one half 
of all the fish caught. This is the shortest half-range, and it 
is the best expression for the average size of the fish caught. 
Calculating these half-ranges for various periods, we get 
the following results :— 
Period. laueaaiaaal Shortest half-range. Over 20 cms. long. 
i % 
1908-1913 19-23 72 
1914 | 17-22 68 
1915 | 17222 54 
1916 20-25 82 
1917 17-21 49 
Now, 1916 was an exceptional year, and the numbers of 
plaice caught by Captain Eccles in the months September 
and October (which are those dealt with) were rather small. 
Considering the other years we see at once, not only from 
the half-ranges, but also from the percentages of all the plaice 
that were over 20 centimetres in length, that the average 
sizes ran smaller and smaller during the period 1908-1917. 
It must be admitted that this result was unexpected. It 
will be very interesting, when some years have elapsed, to 
consider these variations, year by year, throughout the whole 
period from 1908 onwards. In the meantime it would appear 
that not only does the actual abundance of plaice undergo 
variations from year to year, but also that the average sizes 
of the fish undergo concomitant variations. 
Certainly, durmg the period of war conditions, the 
quantities of plaice landed by inshore fishing vessels have 
