280 



PLANKTON STUDIES IN EELATION TO 



TABLE SHOWING FLUCTUATION OF PRINCIPAL ZOOPLANKTON 

 AT STATIONS E. 5 AND E. 6. 



May Cruises. Yeaiis 1903-7 Inclusive. Surface Hauls only, 

 from the international bulletins. 

 The first column shoivs the comparative value sign, the second the adopted nuinerical value. 

 1903 1904 1905 1906 1907 



Species. 



Acartia clausi 

 Calaims fiimiarchicus 

 Centropages typicns 

 Paracalanus parvus 

 Pseudocalanus 



elongatus 



Total mini, value 

 Mean value 



210 



300 



255 



700 1210 

 955 



1200 1110 

 1155 



120 



60 



1210 710, 

 960 



In order to form a wider comparison the results obtained from all the 

 May cruises since the commencement of the International Investiga- 

 tions in 1903 have been included in the present curve. 



When compared with the mackerel landings for May as provided by 

 the official statistics, it will be seen that the correlation between fluc- 

 tuation of zooplankton and that of the fishery is very marked. This 

 would tend to support the suggestion that when zooplankton is in 

 abundance on the fishing grounds mackerel are numerous. 



As already mentioned many more plankton observations were 

 taken during May, 1907, than in the same month of 1906, and as such 

 were actually derived from the fishing area, west and south-west of 

 Scilly (see Samples Nos. 52-55, Table II), they are of value, tending as 

 they do wholly to support the evidence already cited. At every posi- 

 tion within the fishing area the samples taken during a ten-minute sur- 

 face haul were bulky, being composed for the greater part of two or 

 three species of Gopepods, viz. Acartia clausi, Calanus fininarchicus, and 

 Pseudocalanus elongatus, the two latter more particularly, to the almost 

 complete exclusion of other organisms. At one position west of 

 Scilly (S. 52, Table IV), a ten-minute surface tow-netting more than 

 half filled a sample jar of capacity approximately 300 cc. with these 

 two species, in comparatively even proportion. In connection with 

 this fact it may be mentioned that a steam drifter fishing ten miles 

 west of this position on the same night (May 16, 17) landed four lasts 

 of fish at Newlyn the next morning. 



It is perhaps unnecessary to cite further instances of a similar 

 character. The Food and Plankton Tables and Fluctuation Curve 



