THE OLDER STAGES 145 



refers, as I imagine it must, to the whaleman's barrel of 170 litres, 2-3 such barrels would work out at 

 between 6 and 10 cwt. and 10 such at i-|- English tons. 



Ponomareva (1954) gives the average wet weight of T. inermis in the 15-26 mm. range as 0-57 g. 

 from which it would appear that i|tons of this euphausian would amount to at least 2,600,000 

 individuals, a figure approximating closely to the number of E. superba it seems distinctly likely 

 (see next paragraph) might be crammed into the full stomach of an average-sized southern baleen 

 whale. 



Routh (1949) estimated that the full stomach of a blue whale taken by the floating factory ' Balaena ' 

 in the season 1946-7 and said to measure between 75 and 80 ft., contained roughly 5,000,000 £". superba. 

 He does not, however, give details of their size. Heyerdahl (1932) publishes figures showing that the 

 average weight of the individuals in a krill sample ranging from 28 to 65 mm., a range that might well 

 (p. 139, Tables 24-26) have been represented in this stomach, is o-8o g. from which it would appear 

 that 5,000,000 of these euphausians might weigh as much as 4,000,000 g. or approximately four^ tons. 

 This would not, of course, represent an average figure, since many whales are larger than 80 ft. and 

 many are smaller and (Nishiwaki, 1950) have correspondingly larger or smaller stomachs. Allowing, 

 however, the following broad assumptions (i) that the average population of the large Antarctic 

 baleen whales, as Mackintosh and Brown (1956) have shown, was, at its seasonal maximum, about 

 210,000 over the period 1933-9, (2) that on an average (a very conservative average) each individual 

 of this population spends say 90 days on the feeding-grounds, (3) that each individual fills its stomach 

 once a day, and (4) that the average weight of contents of a full stomach might be 2 instead of 4 tons, 

 it would appear that, at a very low estimate, between 1933 and 1939 the krill were being grazed down 

 at the staggering rate of 210,000 x 90 x 2 = 37-8 million tons a year^ by large baleen whales alone, 

 and in actual numbers at the rate of say 2,500,000 x 210,000 x 90, or over 47 million million. This last 

 figure is almost certainly too low since it takes no account of the very small euphausians, the Sixth 

 Furcilias and early adolescents up to 20 mm. long, upon which the whales feed more or less heavily 

 during the early part of their sojourn in the south. It is distinctly possible in fact, that in sheer 

 numbers the krill are being destroyed by the southern whales on a vastly greater scale than has been 

 estimated here. At Station WS 540 Gunther found that in a sample from a patch of yearling E. superba 

 ranging from 17 to 32 mm. (with a 30% mode at 24 mm.) there were 11,152 euphausians to the litre. 

 An average-sized whale gorged to repletion on such a patch, and probably having eaten at least 

 1000 litres would, therefore, be carrying substantially over twice Routh's estimated 5,000,000. The 

 whales, of course, do not feed exclusively on such patches, but (p. 143, Fig. 14) they often do, as 

 well as on patches of much smaller individuals, and this must be borne in mind in any estimate of the 

 total destruction they wreak. I would emphasise, too, that both Vangstein (1956) and Ruud (1956) have 

 already expressed the opinion that Mackintosh and Brown's estimate for the Antarctic whale popula- 

 tion may be too low, and if it is, then my estimate for the annual toll it exacts from the krill could be 

 correspondingly low. Ruud writes: 



There is reason to stress that Mackintosh & Brown's results must be accepted with all possible reservation. It is 

 possible that some of the best whaling fields have been poorly covered by the 'Discovery 11' cruises. The number 

 of whales they sighted, 2602, along a course of nearly 47,000 nautical miles, seems small. . . . But with all possible 

 reservations we are bound to assume that Mackintosh & Brown have reached a correct order of size in their estimate 

 of the stocks. They amount to some hundreds of thousands. 



1 Using Ponomareva's figure for the average wet weight of 15-26 mm. T. inermis, and assuming that to be the same as in 

 the corresponding length range in the southern krill, Routh's 5,000,000 euphausians would weigh 2-8 English tons. 



' Assuming a weight of say 50 tons for an average-sized whale this estimate in fact seems very low indeed when 

 compared, for instance, with the 18 kg. of animal food required in the course of a year's feeding (Petersen, 1918) to produce 

 I kg. of plaice. 



13 DM 



