426 SECTIONAL TRANSACTIONS.— D. 



SECTION D.— ZOOLOGY. 



Thursday, August 18. 



Presidential Address by Dr. 8. W. Kemp, F.R.S., on Oceanography and 

 the fluctuations in the abundance of marine animals (lo.o). (See p. 85.) 



Mr. C. F. HiCKLiNG. — Applications of our knowledge of the biology of 

 British food fishes ( 1 1 .0) . 



The paper first describes the principles of the two most important types 

 of fishing gear — namely, the drift net and the trawl, and points out the 

 limitations of these gears when their results are used as samples of the 

 populations of fish in the sea. But bearing these limitations in mind, 

 the results of the fishing operations of the commercial fishing fleets may be 

 • used to keep a watch upon the state of the fish stocks available for capture. 

 Moreover, these results, when interpreted in the light of the biology of the 

 fish, may be used to predict the future course of the fisheries. These 

 points are illustrated by reference to the herring, haddock, cod, and hake. 



Mr. M. Graham. — The rational exploitation of the fisheries (11.40). 



Statistics of trawl fisheries, such as those of haddock and plaice at Iceland, 

 tend to show eventually that the response to increased fishing effort is, if 

 anything, a decreased yield. 



This phenomenon can be easily explained in terms of age-composition 

 and growth-rate of stocks, which in many cases are available from investi- 

 gations. 



The whole theory may be expressed by the ' logistic ' curve and its first 

 derivative, which can be derived from the two assumptions (i) that the 

 weight of stock that an area can support is limited, (2) that the rate of natural 

 increase of a stock — reproduction plus growth minus natural mortality — is 

 proportional to the difference of weight of the stock at a given moment and 

 the limiting weight that the area will support. This theory has been 

 applied to the marketable species of the North Sea, taken together, in order 

 to estimate the present waste of fishing effort and the maximum yield. 



Important implications are that unless the rate of fishing, including the 

 mesh and form of nets and power of vessels, be controlled, the profit of 

 undertakings is kept at a low value. Without control, gambler's optimism 

 in this industry tends to keep the rate of fishing as high as possible and the 

 profit consequently at an extremely low level. Conversely, however, there 

 is a possibility of a large profit in concerted action to avoid the expenditure 

 entailed in keeping the rate of fishing high. 



A start has been made, in that most of the European countries concerned 

 have signed a convention agreeing to use the minimum mesh allowed in 

 Great Britain. The investigations which show the efficacy of this provision 

 are briefly described. 



Dr. J. B. Tait. — Significance of the physico-chemical environment in 

 fisheries research (12.15). 



Afternoon. 



Prof. T. W. M. Cameron, — Some fish-carried Trematodes in Canada (2.15). 



The great number of fresh-water lakes in Canada, its varied fish fauna 

 and its variety of fish-eating mammals and birds, have made possible a large 



