THE OLDER STAGES 147 



Kritzler (1952) gives Interesting figures for a y^-ft. Pilot whale which died after 9 months in a Florida 

 aquarium having grown a foot in length, put on 200 lb. in weight and eaten 7 tons of squid at an 

 average rate of | cwt. a day. 



The weakest link in this argument is perhaps the assumption that the whales fill their stomachs 

 once a day, although the error involved might to a large extent be offset by the conservative figure 

 put for the average time they spend on the feeding-grounds. Even this assumption, however, is not 

 without some substance, Nishiwaki and Oye (p. 45) having noted a distinct tendency for afternoon- 

 caught Antarctic whales to have the stomachs empty and concluding that both blue and fin whales 

 are in the main early morning feeders and that (whether they fill their stomachs daily or not) they feed 

 at least once a day. Nemoto (1957, 1959) also finds a tendency towards early morning feeding 

 in the baleen whales of the northern Pacific, with decreased activity during the daylight hours and 

 increased activity, not however always distinct, in the evening. It is perhaps of interest, therefore, 

 to recall that it was maintained by the gunners of the old Arranmore Whaling Company, County 

 Mayo, that the baleen whales they hunted were most plentiful on the surface at sunrise (Lillie, 1910). 



Obviously, however, the whole question calls for a comprehensive programme of weighing, 

 counting and measuring of euphausians from Balaenopterid stomachs. There is much need too for 

 extensive observations on the feeding habits and for data on the state of digestion of the krill that are 

 swallowed. A stomachful of uniformly fresh euphausians, for instance, would indicate a recent single 

 meal, and if this condition were observed to occur regularly at certain hours then we might be able 

 to tell the approximate time or times when the feeding took place. In the hake, as Hickling (1927) 

 has shown, weighing experiments indicate a fall in the mean weight of the stomach contents about 

 midday and a tendency for the stomachs to be heaviest about midnight. From this and the fact that 

 their prey was usually freshest in the morning and most ' cooked ' in hauls later in the day Hickling 

 was able to deduce that hake are night feeders. 



As Clarke (1954) has said, 'When we can arrive at some reliable estimate of the size of the whale 

 stocks, and have somehow found out the rate of feeding, this information could be combined with 

 studies on growth and size distribution to calculate and compare the total annual consumption of food 

 and the total annual increment of whale tissue '. 



Summarising, the large southern baleen whales feed on krill ranging from larvae at the Sixth 

 Furcilia stage, no more than 1 1 mm. long, up to adults of the largest size, 60 mm. long or more. 

 The bulk of the diet, however, or ' staple whale food ' as I shall call it, seems to consist of euphausians 

 over 20 mm. long. The smaller (larval and early adolescent) forms which provide an important 

 contribution to the feed in spring, the so-called 'blue whale krill ' (Ruud, 1932) of the South Georgia 

 whalers, I shall refer to collectively as ' the small whale food '. 



Influence on the foetal growth-rate of whales 

 Laws (1959 a ; 1959*) has recently shown that during the last 5 months of pregnancy the foetal weight of 

 southern blue and fin whales increases with unparalleled rapidity, the weight of the blue foetus rising 

 in that time from 20 to 2500 kg., a gain of 2-44 tons, of which over two are put on in the last 2 months. 

 It is interesting, as Laws remarks, that the beginning of this phenomenal burst of grovv^th should 

 coincide with the advent of the mothers upon the richly spread table of the Antarctic feeding-ground. 

 On the slenderest of grounds Naaktgeboren, Slijper and Utrecht (i960) express the view that the 

 'remarkable deflection in the curve of Laws (1959, 1959*) is likely to be a result of the small number 

 of foetuses involved '. Laws' very accurately measured material, 1 1 12 blue and 956 fin whale foetuses, 

 could hardly in fact be called small, and, replying to his Dutch critics (Laws, 19606), he notes they 

 seem to have missed the main point of his paper on foetal growth. 



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