SEA-FISHERIES LABORATORY. 403 



rocks and banks, and these are just the places where of 

 recent years it has been found that plankton is also most 

 abundant. 



Any naturalist cruising on the West of Scotland 

 (and no doubt in any other region where there are strong 

 tides) could scarcely fail to notice the way in which the 

 gulls and other sea-birds congregate where the currents 

 run most strongly and where there are swirls in the 

 water, indicating rocks or an uneven bottom, and 

 resulting vertical movements of the water. These sea- 

 birds are found to be feeding upon young fish, and the 

 fish are there because the plankton is unusually abundant. 



A definite connection seems to have been established 

 on the coast of Cornwall, by Allen and Bullen, between 

 the results of the mackerel fishery and the occurrence of 

 Calanus in the plankton. There is some evidence that 

 on the West coast of Scotland there is a similar 

 connection between herring shoals and abundance of 

 Calanus. The matter is well worthy of further investi- 

 gation. 



5. Plankton and Movements of Fishes. — Many 

 groups of the plankton, and especially the zooplankton, 

 it is now known quite definitely, are distributed in 

 swarms, notwithstanding various assertions to the 

 contrary. In our coastal seas at least, where the 

 fisheries we are interested in take place, the plankton is 

 not uniformly distributed. Various localities and depths 

 are characterised at different seasons by particular 

 assemblages of plankton, and it is reasonable to believe, 

 in view of the facts given above as to the association of 

 fish and plankton, that these variations in the distribu- 

 tion must have a marked effect upon the presence and 

 abundance of at least such fish as herring and mackerel, 

 and also of the shoals of post-larval young of many 

 valuable demersal fishes. 



