C-24 



KRILL PRODUCTION 



Total predation on krill by fish, squid, birds and 

 mammals amounts to approximately 330 x 10" tons per year. 

 This value is an estimate of production by the krill popu- 

 lation . 



The ratio of annual production to average biomass is 

 an estimate of turnover rate for the krill population. Pro- 

 duction estimated by predation is roughly equal to the ave- 

 rage standing stock and about half of the peak annual bio^ 

 mass. Turnover of 50 to 100% of the population in a year 

 is slow for marine zooplankton. However, Antarctic krill 

 are long-lived in comparison with other zooplankton, so 

 this figure is not so surprising. 



The questions of krill life span and age of sexual 

 maturity are not yet resolved. Data on size distribution 

 can be interpreted in several ways (Fraser, 19 37 •, Bargmann , 

 1945; Ivanov, 1970). Krill do not breed until the beginning 

 of their third or fourth year, lengths of 28 to 45 mm, and 

 may breed one or two seasons (McVJhinnie, letter to K. Green, 

 18 October 1977). 



Life span questions affect estimates of krill replace- 

 ment rates and consequently estimates of sustainable yield. 

 With present uncertainty on development rates, the propor- 

 tion of the population that is capable of reproducing in 

 any year cannot be determined. 



