THE WESTEEN MACKEKEL FISHEKY. 



279 



ing a close comparison, to consider only such observations as are com- 

 mon to the two years. These are furnished by the analyses of plankton 

 samples taken at the mid-Channel and Bristol Channel stations (Stats. 

 E. 5 and E. 6) during the May cruises of the International Plankton 

 Investigations. 



By the same method of comparison as adopted for other similar 

 cases (see page 272) a curve was formed, showing the fluctuation of the 

 principal zooplankton forming mackerel food. This curve (Fig. 1) 



PLANKTON 



VALUES 



1200 



lOOO 



800 



600 



'too 



200 



MACKEREL 

 CWTS. 



400.000 



350,000 



300,000 



250,000 



200,000 



150,000 



1905 



1904 



1905 



1^6 



100,000 



1907 



Fig. ]. — Curves showing, for the month of May, fluctuations in the quantities of mackerel 

 landed, and of zooplankton observed at Stations E. 5 and E. 6. 



ZooplanVton : mean between Stations E. 5 and B. 6 for May — Dotted line. 

 Mackerel landed during May — Continuous line. 



shows the results of a mean between the analyses of the samples 

 taken in surface hauls at the two stations, the following species only 

 being taken into consideration : Acartia clausi, Calanus finmarchi- 

 cus, Centrojjages typicus, Paracalanus parvus, and Fseudocalanus elon- 

 gatus. 



