SECTIONAL TRANSACTIONS.—D. 449 
species, in these variations of absolute abundance and time of culmination of 
the invasion, and each species appears to be affected differently by the environ- 
mental conditions. The factor influencing actual abundance appears to be a 
statistical one—a chance association of sub-factors, and not at all any single 
physical event, or even a few main physical events, in the sea. 
8. Mr. B. Storrow.—Age, Growth, and Maturity of Herrings. 
The 1918 year-class of the North Sea in 1920-21 divided into two sections; 
one migrated north, the other south. The northern section grew rapidly in 
1921-22. The area of greatest growth was west of the passage between the 
Orkneys and Shetlands. Growth is influenced more by environment than 
heredity. Atlantic water activity is followed by a prolonged spawning 
season, formation of new spawning grounds, more extensive or more obvious 
migrations, and a mixing of shoals. The formation of races in the North Sea 
is a physical impossibility. Spring spawners of the Forth come from northern 
waters, and so do the East Anglian shoals. Whilst the conditions of the year 
preceding hatching are held to be of the most importancs in the production of 
good year-classes, those occurring in the herring’s third year may modify the 
yield from the fishery. 
9. Dr. Marie Lesour.—The Feeding of some Plankton Organisms. 
Living plankton organisms, consisting chiefly of Celenterates, were kept 
alive in the laboratory in plunger jars, in order to study their food and methods 
of feeding. Others were examined fresh from the tow-nets. It was found that 
a large number of species of Meduse were able to capture and digest small 
larval and post-larval fishes; this applied also to Pleurobrachia, Sagitta, and 
Tomopteris. Aurelia, from the scyphistoma and the smallest ephyra up to a 
breadth of at least an inch and a quarter, was able to feed largely on fishes ; other 
Medusez, beginning at less than a millimetre across, were eating young herrings, 
sprats, and sand-eels. It is thus shown that many of these plankton organisms are 
true enemies of the little fishes, although most of them, practically omnivorous, 
are able to eat a variety of other food. 
10. Mr. A. C. Harpy.—Plankton in Relation to the Food of the 
Herring. 
As part of the general scheme of investigations at present being carried out 
by the Ministry of Agriculture and Fisheries into the natural history of the 
North Sea herring, a study has been made of its food at all ages, and that of 
the mature fish at different seasons of the year. Plankton samples have been 
taken simultaneously with the catch of fish, and selection of food in the plankton 
is shown to take place by both young and adult fish. The change of food 
during the period of growth and throughout the year is described and such 
points as the following discussed : the apparent dependence of the young post- 
larval herring on the copepod Pseudocalanus elongatus ; the suspension of feed- 
ing in the spawning season; the preference for small fish, notably sand-eels, 
rather than copepods in the spring; the importance of Oikopleura; the distribu- 
tion of the principal food forms and, briefly, the relation of the herring to the 
plankton in general. 
11. Mr. J. N. Carrutuers.—North Sea Currents in Relation to | 
Fisheries. 
In view of the fact that the economics of a fishery are bound up in the 
fate of the passively floating eggs, larve, and planktonic food materials, many 
investigations into the nature of the currents of such an important fishing area 
as the North Sea have been made. 
Valuable work by Fulton, some twenty-five years ago, threw light upon the 
source of the plaice stock of the Scottish coastal areas. 5 
The Ministry of Agriculture and Fisheries emharked, in 1920, upon an 
extensive experiment designed to elucidate the non-tidal movements of both 
surface and bottom water in the southern North Sea. Drift bottles, both of 
the surface-floating and bottom-trailing types, were put out from each of seven 
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