SEA-FISHERIES LABORATORY. 105 
the Copepoda—in some cases in the proportion of about a 
thousand to one. It must be remembered, however, that the 
Copepoda are individually much larger and so may be of 
greater importance in the plankton as a food material. 
In looking at the total numbers recorded of the selected 
Copepoda we find that Oithona is the most abundant and 
Pseudocalanus comes next. Calanus is the least numerous in 
individuals, but that is probably made up for by its very large 
size. It certainly seems to be of great importance as a food 
for migratory pelagic fishes. We have given an example 
above of the connection between Temora and the herring. 
The Copepoda, as a whole, are a summer and autumn 
group, all the crests of their annual curves being found between 
May and October—the time of year when the post-larval fish 
of that season are growing up and when shoals of herring and 
mackerel appear in the coastal waters. The association of 
shoals of fish with abundance of zooplankton is the result of 
the fact that, in order to get an adequate quantity of plank- 
tonic food, the fish must seek out and capture the Copepoda. 
In other words, the plankton-feeding fish must go where the 
plankton is sufficiently abundant and must in their migrations 
follow the movements of the swarms of Copepoda. 
Consequently, it is of importance to show, as we now can, 
that in our coastal waters at least, where the fisheries we 
are interested in take place, the plankton is not uniformly 
distributed. Many kinds of Copepoda occur very definitely 
in local swarms, and various localities and depths are charac- 
terised at the different seasons by particular assemblages of 
plankton. It is, therefore, reasonable to believe, in view of the 
facts given above as to the association of fish and plankton, 
that these variations in the distribution must have a marked 
effect upon the presence and abundance of, at least, such 
migratory fish as herring and mackerel, and also of the shoals 
of post-larval young of many of our other food fishes. 
