SECTIONAL TRANSACTIONS.—D. 401 
importance in that they would provide physiological barriers—lines of cleavage in an 
otherwise homogencous population—thus aiding the spread and establishment of any 
new variants which might arise. 
There are a number of cases in which true biological races appear to have been 
induced experimentally. In most of these cases a Lamarckian explanation has been 
suggested. As regards insects there does not seem to be any one instance in which 
all other theories are completely ruled out, but there are one or two cases concerning 
plant feeding Nematodes which seem to make a Lamarckian explanation much more 
difficult to dispense with. 
Taken as a whole the phenomenon of biological races seems to provide a con- 
siderable amount of circumstantial evidence for some form of Lamarckian theory. 
Dr. O. W. Ricnarps.—Geographical Races and Evolution. 
Prof. D. M. 8. Watson. F.R.S.—The Evolutionary Importance of the 
Study of Lineages. 
Prof. J. B. S. Hatpane.—The Genetical Analysis of Interspecific 
Differences and the Mathematical Theory of Evolution. 
Wednesday, September 30. 
Symposium on The Past and Present of the Overfishing Problem. (Prof. 
W. Garstane, F.R.S.; Dr. A. Bowman; Dr. E. 8. Russett.) 
Dr. A. Bowman.—The Haddock Population of the North Sea. 
The haddock population of the North Sea plateau may be regarded as a self- 
contained one, and changes in its population can be studied without reference to 
contemporaneous changes occurring in such haddock producing regions as Faroe, 
Iceland, etc. 
A census of the total population in this area during the last ten years has been 
obtained by a combination of three methods :— 
1. Collection of statistics and measurements of fish landed at the various markets. 
2. Ichthyometrical observations at sea on selected vessels to ascertain the pro- 
portions of unmarketable sizes in the total catches. 
3. Periodic trawling surveys by the Scottish Research Vessel to obtain scale 
material and data with regard to the smaller sizes of fish which escape capture by 
the ordinary commercial gear. 
The market statistics collated in a series of monthly charts by the Ministry of 
Fisheries (England) form the basis of the scheme. Each fishing vessel providing 
information is in effect a research vessel. The debt we owe to the friendly co-operation 
of the industry in the collection of such comprehensive data is incalculable. 
Scale-age-assessment of the voluminous data has been accomplished by the 
examination of copious representative samples. 
The most striking feature of the annual recruitment of the population is the 
enormous variation in its incidence. The ratio of the most successful brood to the 
least successful has been of the order of approximately 50 to 1. Briefly summarised, 
the period has produced three exceptionally good spawning years and five poor ones 
for brood survival. 
No direct relation can be shown to exist between the weights of the spawning 
shoals (numbers of eggs produced) and the respective numbers of the broods surviving 
to reach the sea floor. Under favourable natural conditions, the weight of spawning 
fish has been sufficient to yield a bounteous crop of baby haddock. Regional 
differences in growth rates in the earlier years of life remain consistent to type and it 
cannot be inferred from the investigations that variations in these regional differences 
from year to year arise from variations in the densities of the respective broods. 
The entry of a brood of great numerical strength into the marketable stock, 
particularly if it follows bad brood years, is immediately reflected in the ‘ quality’ 
1931 DD 
