PROGRESS IN BIOLOGICAL INQUIRIES, 1926 605 
Maine, perhaps 700 of these fish will stay at home until they are 
caught—they will be recaptured a week or a month, a year or two 
years later—but some of those fish, for reasons unknown, will start 
to migrate, and it is impossible to say why. The same thing happens 
-to our Nantucket fish; some will migrate and others will stay on Nan- 
tucket Shoals. At first we thought the varied temperature was an 
important factor, and the coming of fall and winter would cause the 
fish to migrate to warmer waters; but we are mistaken in that, be- 
cause the maximum temperature is not reached until late fall, and that 
is about the time the fish start to migrate west and south—when the 
weather is actually warmest. Unless they have an instinct which 
sends them on these migrations, I can not find any reason why they 
should migrate west and south. 
Doctor Gitprrt. Is the nuntber of straggling fish great enougli to 
indicate migration ? 
Mr. Scurorprr. I really think it is. I think the reason the strag- 
eling fish are often recaptured is because the fishermen go to those 
banks were many of them migrate and catch the fish. Perhaps 
some go to places where no one fishes—places seldom visited by 
anyone. 
ae Gitpert. About this different rate of growth in the south- 
ern and northern fish; did I understand you to attribute that to food 
rather than any racial habits? 
Mr. Scurorper. It may be to food and temperature combined. I 
do not think it is racial habit. I really can not answer that question 
at this time, although I hope to at some later time. Unmistakably, 
southern fish do grow faster than northern fish. 
PLANKTON INVESTIGATIONS 
By Dr. CHARLES J. FISH 
The plankton investigations that form a part of the bureau’s North Atlantic 
program have two basic objects: 
1. To determine the relative value of the various cod “ banks” as production 
centers, and to determine whether local production is sufficient to maintain the 
inshore stock along the New England coast or whether it is dependent for its 
supply upon immigration from the offshore spawning grounds. 
2. To. investigate the factors that cause success or failure in the annual 
production of young fish (high or low breeding years), as indicated by the 
variations in the catches of the various “age groups.” 
The results of extended investigations by Norwegians have shown the 
existence of an intimate relation between the fluctuations in the numerical 
value of the fish stock and the yield of the great fisheries. This makes it 
possible to determine the fluctuations in the renewal of the stock from year to 
year by determining the numerical value of the various age groups in the 
catches. 
My problem is concerned with what causes these fluctuations from year to 
year in the supply of fish and where are the sources of supply. Obviously 
the fate of any group that has pelagic young is solely dependent upon the 
success or failure of the young to maintain themselves in the plankton. There 
must be ample food available, and the winds and tides must remain favorable 
at least until they reach the stage when benthonic life begins. 
In European waters it has been shown that the actual quantity of eggs pro- 
duced is often not in itself a factor sufficient to determine the numerical value 
of a year class. A rich spawning year may produce a year class poor in num- 
bers, while a large year class may have its origin in a year when the spawning 
was at its lowest. This has been observed repeatedly in the water about 
Lofoten. However, it has also been determined that we must look to the early 
