24 
BULLETIN OF THE BUREAU OF FISHERIES 
It does not follow from this, however, that all parts of the gulf are equally favorable 
as marine nurseries. On the contrary, few if any animals breed indifferently or 
equally plentifully over its whole area, and different parts of the gulf may run the 
whole gamut from extreme productivity to almost complete sterility for one species 
or another. Our work has not progressed far enough to give more than a glimpse 
of such local differences; enough, however, has been done to show that the south- 
western corner of the gulf generally, and the Massachusetts Ba}^ region in particular, 
stand at one extreme, with innumerable copepods and a great abundance of pelagic 
fish eggs produced there (not to mention other planktonic animals), while certain 
small areas in the Bay of Fundy exemplify the other, where few if any animals with 
floating eggs breed successfully. Broadly speaking, our hauls have demonstrated 
that the coastal belt, out to the 100 or 150 meter contour, is more prolific than the 
deep trough in the production of planktonic animals. 
VERTICAL DISTRIBUTION OF THE ZOOPLANKTON 
In the foregoing lines the various planktonic communities are treated as though 
their several component groups or species were indifferently distributed from the 
surface downward, independent of depth; the various lists, that is, are such as would 
be yielded by vertical hauls from surface to bottom at the respective stations. Such 
is by no means a true picture, however, for it often happens that, although the 
species from any given locality occur side by side geographically, they may be far 
apart bathymetrically, and especially so in the deeper parts of the gulf. Nor is it 
astonishing, with a pelagic fauna as varied as that of the Gulf of Maine, and with its 
sundry members responding variously in their vertical occurrence to the physical 
conditions under which they live, that we have usually found the plankton of mid- 
summer more or less stratified even in the upper 100 meters or so, either by the 
concentration of one group of animals at one level, another group at another, or by 
a comparatively barren state of the immediate surface contrasted with great pro- 
ductivity in the underlying strata of water. The stratification between depths less 
than 100 meters, on the one hand, and the bottom waters of the gulf, on the other, 
is still more significant, being one of kind as well as of degree, as I shall endeavor 
to make clear later (p. 26). Indeed, it would not be too much to say that the local 
zooplankton is never quite uniform from the surface downward to any considerable 
depth, unless it be in very shallow water or in localities where vertical circulation 
keeps the whole column effectively stirred from top to bottom. 
With so many subjects involved, stratification, whether quantitative or quali- 
tative, may occur in infinite variety, and many instances of the sort have forced 
themselves on our notice, though our hauls have not been particularly directed 
toward the detection of such. Perhaps the most interesting phase of the subject, 
as it is certainly the most widespread, is the scarcity of adult pelagic animals of 
the Calanus community, including most of the species which together make up 
the preceding plankton lists (p. 17), at the surface during the daylight hours of 
summer. No matter what nets we have used on the surface between sunrise and 
sunset in the offshore waters of the gulf at this season, they have usually yielded 
very little zooplankton of any kind, and often practically nothing except larval 
