SECTIONAL TRANSACTIONS.—D. 493 
success in survival of broods some years previously. The proportion of 
particular broods is estimated when the fish are large enough to be taken 
in trawls. Having found that the important fisheries depend on fish of 
a restricted age, say, five to six years old, estimates of the yield at that age 
can be made some years in advance, from the abundance of fish of, say, 
one to two years old. 
The particular case considered, the cod in the North Sea, is interesting 
in that : 
(1) The area populated by small fish is so extensive that adequate sampling 
of small cod can only be obtained in the trade statistics of landings, cause 
being shown for considering the magnitude of certain seasonal changes in 
the statistics as a measure of brood strength. 
(2) The age of the cod (by which landings of small cod are related to 
brood years and to subsequent yield of large cod) has to be obtained in- 
directly, from size ; partly because of the said sampling difficulty and partly 
because the more usual determinations of age from scales or otoliths are un- 
reliable for this fish (in the North Sea). The necessary analysis involves 
somewhat unconventional methods, which are, however, justified by the high 
correlation found. (See (3).) 
(3) Formulz are deduced from the investigations of (1) and (2) and relate 
brood strength to subsequent yield per unit of fishing power, in a perfectly 
rigid manner, so that, up to a point, the prediction is precise and depends 
merely on arithmetic (its precision being estimated by prediction of the 
‘probable error’). High correlation has been found between the estimate 
of brood strength and subsequent yield, 
Mr. E. Forp.—Growth in length and change in form with increasing age 
in fishes, especially the herring (2.45). 
The communication deals with changes in form brought about by the 
different rates at which the various parts of a fish’s body increase in length 
during the transition from a transparent larva to a fully scaled adolescent, 
and with the subsequent growth in length of the body as a whole, by the 
addition of progressively diminishing annual increments throughout life. 
Simple mathematical treatment of observed data raises interesting questions 
in phylogeny and ontogeny, and suggests a convenient method for the 
comparison of growth in different geographical regions. 
Dr. C. H. O’DonocHuE.—Fasper Park, Rocky Mountains : its biology 
and fisheries (3.15). 
In 1925 the Biological Board of Canada requested the author to investigate 
the lakes in Jasper Park with a view to improving their fishery value. It was 
considered worth while to conduct the examination on broad lines, since 
no similar survey had been made within a radius of 2,000 miles, and the 
mountainous character of the country, its altitude and essentially virgin 
conditions made it unique in North America. This report covers two 
summers’ field work and their results. One noteworthy problem was the 
entire absence of fish from the Maligne-Medicine drainage system. The 
answer to this question was found in the peculiar geological conditions of 
the outlet of this system into the Athabasca valley, whereby the system is 
cut off from the possibility of fish immigration. A fairly full investigation 
of the physical and chemical constitution of certain types of lakes was made 
and also a survey of their flora and fauna. Resulting from the survey 
