402 SECTIONAL TRANSACTIONS.—D. 
of the catches. The percentage proportions of ‘ extra-smalls’ and ‘ smalls’ in the 
market landings shoot up rapidly. 
The results of the age analysis of the market landings bring out clearly that the 
North Sea haddock fishery is dependent for the most part on the exploitation of young 
fish from two to four years of age. There is a progressive and rapid decline in the 
yield of a brood after the third year. 
The modern trawl, the apparatus of most importance in the haddock fishery, 
takes toll of the population before it has grown to marketable size. Thinning of the 
unmarketable sizes begins before the end of the first year of life, is of greatest magnitude 
in the second summer, and ceases in the early summer of the third year as laggards in 
growth attain marketable size. 
The gear used effects total capture of sizes much less than that of mean size at 
first maturity and also less than that of minimum marketable size. Large numbers 
of small haddock are, therefore, destroyed annually in the course of normal fishing 
operations, the magnitude of the destruction varying with the numerical strengths 
and rates of growth of the upgrowing broods and with the incidence and intensity of 
fishing. 
To the annual production of haddock by the region as measured by the weights of 
fish landed there must be added the weights of fish caught and returned dead to the 
sea. 
The haddock as a weight producer is improving in efficiency during the first years 
of life. If only half of the unmarketable sizes destroyed at present escaped and were 
captured one year later the same weight of haddock but of greatly enhanced market 
value would be obtained. Since the numbers of brood present in a particular area 
have no marked effect on the mean rate of growth a haddock just under marketable 
size alive in the sea is of greater potential value than a dead one. 
The process of elimination is the same whether the brood is rich or poor in numbers, 
and during the period under review there have been three rich broods when thinning 
might have had some small effect on the rate of growth of the uncaptured stock, but 
there have also been five meagre broods when thinning undoubtedly accentuated the 
depression arising from the initial deficiency in numbers. 
The present method of exploiting the haddock population of the North Sea plateau 
is wasteful, squandering the riches of years of good brood survival and accentuating 
the depressing effects following years of scanty brood production. 
Fluctuations in brood production are inevitable, but by postponing the time of 
capture of the young growing stock the average age of the marketable stock would 
be raised and the fishery, dependent on a larger number of age classes, would thereby 
have greater stability. 
Dr. E. S. RussEtu. 
The overfishing problem now appears to us as much more complicated than it 
did in the past. We have learned to regard it as a complex problem of ecology. The 
main factors affecting the abundance and average size of the fish composing a stock 
are (1) intensity of fishing, (2) the supply of young fish, (3) rate of growth. All these 
factors are subject to variations. Theoretically there is for each state of a stock an 
optimum intensity of fishing, and an optimum size at which to begin capture. Our 
knowledge is so far insufficient to state what these optima are, and they obviously 
vary according to conditions. Wasteful destruction of fish is to be avoided, par- 
ticularly the destruction of fish just under a commercially valuable size. Our aim 
should be to obtain every year the maximum yield which is compatible with main- 
tenance of stocks at a steady productive level. 
Symposium on Insects and Human W elfare :— 
Dr. A. D. Imms, F.R.S.—Insect Behaviour in relation to Control 
Measures. 
Mr. J. ©. F. Fryer.—Practical Achievements in Agricultural 
Entomology in Britain. 
In England the modern era in agricultural entomology (including horticultural 
entomology) began some twenty-five years ago, and the subsequent period has been 
