F-18 



that for euphausiids in general the best estimation technique is that based on the calculated 

 nvunber of egga whose volume is equal to half the mature ovary and that the ripe ovary occupies 

 about 10^ of the body volume. Makarov (1975) states that the eggs released amount to 34-39?^ 

 of the body wei^t in E. superba which, assuming that wei^t is proportional to volume and 

 that eggs have a volume of 1 x lO"'^ ml, indicates a very much higher fecundity. This estimate 

 is in closer agreement with the results of Nauraov (1962) who counted ripening eggs present in 

 the ovary. The estimates are compared in Table 6.5. The fi(^e of over 11 000 detarmined 

 by Bargnann (1937) is probably an estimate of all the eggs at all stages present in the ovary 

 rather than an estimate of the number that would actually be released. This figure has there- 

 fore not been included in the tabulated results. 



Table 6.5. Fecundity of Euphausia superba . Data from Mauchline and Fisher (l969)t Makarov 

 (1975)1 Haumov ( 1962) and Hemoto et al (in press). 



It is not clear what is the reason for the enonnous variation in the estimated values of 

 fecvmdity. The egg size noted by Naumov (I962) in the ovaries of the individuals he examined 

 would indicate that the eggs released represent nearly 60^ of the body volume. The release 

 of such a large proportion of the body volume as eggs just prior to the winter season seems 

 unlikely if the same individual is going to spawn a second time in the following spring. On 

 the other hand the general figures derived by Mauchline and Fisher (1969)1 as they point out, 

 are not always correct and in this context it may be that Ej_ superba is an exception. There 

 is therefore a clear need to identify what proportion of the eggs present in the ovary are 

 released and also to generally improve the refinement of these estimations. 



6.5. Swarming 



The habit of Ej_ superba of forming dense aggregations has been well known for a long time 

 and because of the concentration of individuals within the swarms they are often thou^t of 

 as ideal for exploitation. V/hat is not clear however is the proportion of the total krill 

 population that is present in the swarms nor the absolute density. The former point is vital 

 to resource management and the latter to rational fishing. 



