96 
BULLETIN OF THE BUREAU OF FISHERIES 
'particular day indicates its relative abundance for that day compared with its abundance 
for all the preceding days or weeJcs since its appearance and is not to he compared with 
that of the species of any other phylum. To eliminate as far as possible the confusion 
arising from daily variation, three-day averages were used in plotting the points 
on the charts. There may be objections to my method of presenting the data 
in graphic form where definite figures were not available. However, I feel that the 
seasonal variation can best be shown in this way, and that any method which sim- 
plifies the work and makes it more easily understood is justifiable. The symbols 
used on the charts are as follows : F. very abundant; J.., abundant; /S., scarce; 
V. S., very scarce; and N., none. 
LOCATION 
All material for the present investigation, with the exception of a few observa- 
tions made in Vineyard Sound, was obtained from the water at the end of the Biireau 
of Fisheries dock at Woods Hole, Mass. This spot was selected, first, because it 
offered such excellent possibilities for qualitative plankton investigation, and, 
second, because the bottom fauna, whose larvje make up a large percentage of the 
summer plankton, had already been carefully surveyed. 
The location is an exceptionally fortunate one for an investigation of seasonal 
distribution, although impossible for a study of diurnal migration. On the flood tide 
the local ciurent rushing through the narrow passage of Woods Hole sometimes 
reaches a speed of 8 miles an hour. Figure 1 shows that one of the three main 
branches of this current heads directly for the Fisheries dock. Here it divides, 
one half turning to the south and the other to the north. By placing nets at the 
two ends of the dock one hour after the tide has turned to flood and hauling them 
one hour before the ebb it is possible to have a strong cmrent of water passing 
through the nets continuously for four hours. More material can be collected in 
this way than would be possible in several hours' towing from a boat. To deter- 
mine the complete pelagic fauna of a region, the largest possible number of daily 
samples are needed. Even then many scarce forms probably pass through their 
seasonal cycle without once being observed in surface collections. 
Another advantage of the position of this particular station is the uniformity 
of the plankton both during the day and during the night. Extended observations 
showed that the mixture of the waters during the flood tide so churns up the plankton 
that there is almost no difference between the hauls of the day and those taken in the 
evening. I know of but two exceptions to this statement. These are the amphipods 
and certain annelids, which remain under rocks in the daylight and emerge after 
dark. Then they are picked up by the strong currents and appear in the greatest 
nxunbers in evening collections. As these are not true pelagic animals, they do not 
seriously affect the problem. Thus, the collections made at any time showed equally 
well the representative plankton for that day.' 
The features of the coast adjacent to Woods Hole have much to do with its 
fauna. It has long been thought that the arm of Cape Cod to the east constitutes a 
barrier that changes the course of the cold northern ocean current and deflects it 
away from the continent. Not all oceanographers agree as to the above, but even 
