THE OLDER STAGES 143 



reason they avoid the latter. It certainly cannot be that it is taken but rejected wholesale by the baleen 

 plates, for growing as it does up to 30 mm. long it is much too big for that. It is bulky besides, being 

 broader in the beam than the slender krill. We do not of course know if the baleen whales can in fact 

 tell one colour from another. It has been suggested, however (Mann, 1946), that colour vision in these 

 animals is a possibility. 



Z 36 



OCTOBER 



NOVEMBER 



19 23 25 30 4 7 9 IS 16 18 22 28 I 2 5 9 P 17 19 28 3 4 5 8 KD 12 



I Scale percent ■ | I | 



i I 1 T °^°° I '1 iiiii 



30 40 40 40 40 40 40 40 40 40 40 70 

 49 216 27 III 58 37 I20 97 



40 40 40 20 40 40 



18 37 42 55 99 79 702 61 



9 40 



lOO lOO I03 NO 42 3IO 



40 40 40 30 216 100 



lOO 100 100 lOO 52 280 27 189 48 379 61 



113 40 116 40 

 116 588 325 522 



DATE 

 68 



64 

 60 



55 \ 

 52 i 

 48 ' 



44 I 



40 ■» 



36 z 



24 a 



20 I 



16 U 



12 "^ 



I 



DATE 



68 



64 

 to 

 ^ 60 



O 56 



cr 



O 52 



2 48 



s '^ 



. 36 



O 32 



< 28 



"^ 24 



f 20 



O 16 



::i 12 

 S 



o 



FEBRUARY 



13 19 20 23 31 2 3 6 II 12 13 14 18 22 23 24 28 I 



^MRCH 



I 7~\ m I 1 



fmuuw 



O so 100 O iO lOO 



Scale per cent 



STOMACH SAMPLE 

 NET SAMPLE 



146 40 40 50 



159 IOC 32 



164 40 40 



171 146 



318 40 

 36 III 



40 207 



122 287 40 



904 86 539 lOO 818 186 82 lOO 



lOO IOC 100 118 



Fig. 14. Length frequencies of krill from the plankton and from whales' stomachs compared, both stomach samples and 

 plankton samples having been collected on the same, or approximately the same dates. The number of older (O) and younger 

 (Y) krill measured is given for each sample. 



The remarkable exclusiveness of the diet of the southern whales is paralleled among many far- 

 eastern fishes, the Pacific cod for example, with over lOo abundant species to choose from, consistently 

 selecting only four or five (Moiseev, 1957). 



As a result of the 2-year life-cycle of the krill the feeding-stuff available to the whales consists of 

 two distinct broods, a younger, rising yearling or yearling class, and an older near-mature or 2-year old 

 breeding stock that is reaching, or shortly about to reach, the end of its natural span. The whales feed 

 indiscriminately on both. Sometimes the young brood is present in the stomachs, sometimes the old, 

 or, as often happens, both broods may be present in the same stomach. In Fig. 14 I have plotted 

 in 4-mm. groups the length frequencies of samples taken from whales' stomachs and compared them 

 with samples taken directly from the plankton on the same, or approximately the same, dates (not 



