PHOSPHATE, PLANKTON AND WHALE DISTRIBUTIONS 



291 



P ? 0, 



should expect if the phytoplankton over the whole area had died down and no longer 

 exerted an influence upon the Euphausians. The Euphausians, which we have supposed 

 were originally concentrated in small 

 areas, would now be free to scatter, 

 so that the whales might find it more 

 difficult to find sufficient food. The 

 mechanism by which plankton animals 

 become concentrated or dispersed will 

 be discussed in a later section ; hitherto 

 they have been regarded as purely 

 drifting organisms. A similar effect 

 might be found if the opposite view 

 is correct, i.e. if the smaller area of 

 higher phosphate content was due to 

 the Euphausians being concentrated 

 at one place and keeping the phyto- 

 plankton in check, and the wider- 

 spread lower phosphate values being 

 due to a lack of Euphausians allowing 

 the phytoplankton to flourish. The 

 whales would be concentrated round 

 the patch of Euphausians in January, 

 but in February they might have so 

 greatly reduced this stock of Euphau- 

 sians as to be forced to scatter widely 

 afield in search of food. 



Before we examine further examples of correlations between whale abundance and 

 high phosphate values we must discuss an issue of considerable interest. If the patch 

 of higher phosphate content, in the survey just described, represents an area in which 

 a lower phytoplankton production had taken place, and so an area of concentration of 

 Euphausians which accounted for the concentration of whales in January, how is it that 

 this patch of higher phosphate content remained in the same place to be recorded in the 

 survey at the end of January and the beginning of February? If the phosphate figures 

 represent what has happened over a considerable interval in the past, it might be ex- 

 pected that this patch would by the action of currents have a position earlier in January 

 a long way away from that which it occupied at the time of the survey, i.e. a long way 

 away from that occupied by the whales. In the open ocean such a patch must change 

 position rapidly, but against an island such as South Georgia swirls would appear to 

 be set up which must maintain their position for a considerable time. Fig. 155 shows 

 concentrations of Fin whales in December-February 1923-4. It is inconceivable that 

 the whales should remain concentrated at one spot in the feeding season without there 

 being concentrations of food there. It is difficult to believe that the concentrations A 



a 16 17 18 19 820 21 22 23 24 25 25 27 28 29 pH 



Fig. 154. Correlations of phosphate and pH values, each 

 averaged for the top 50 m., at stations in the January- 

 February 1930 survey. Those in January are shown as 

 blacked-in circles, those in February as open circles. 



