H-15 



RESEARCH PROGRAMMES 



investigating potential krill fisheries. Recent results suggest that progress has been made towards 

 reducing the problems of locating and catching krill, and that large catches could be taken at 

 moderate cost, provided the fishing does not have to be interrupted to handle and process the 

 catch. However, these latter processes still present formidable problems. 



Studies on a number of biological characteristics, population distribution, swarm 

 characteristics and position of krill in the Antarctic marine ecosystem have largely been 

 conducted during the past six decades by, among others, the United Kingdom, Norway, USSR, 

 and Japan. While considerable information now exists concerning biological parameters, 

 including larval stages and distribution, sexual maturity, spawning, feeding characteristics and 

 regional differences in population densities (Bargmann, 1937, 1945; Fraser, 1937; Marr, 1962; 

 Mackintosh, 1966, 1972, 1973; Ivanov, 1970), there is Uttle reliable direct data on krill growth 

 rate, or growth increment and moult frequencies. Estimates concerning growth have been 

 derived inferentially through extensive studies of class sizes, increases in mean class size with 

 season, developmental phases (larval, adolescent, maturing and breeding adults) and their 

 distributions with rime. The time scale from the first calyptopis to young adolescent stages 

 seems to be established while diverse interpretations have been made from the data of post 

 larval size frequency distribution. Mean values of krill sizes and gonadal development, derived 

 from numerous samples collected during about 10 years and mainly between 20°Eand 70°W, 

 have led to the conclusion that E. superba matures and breeds two summers after being 

 spawned (Bargmann, 1945; Marr, 1962). However, samples collected in the vicinity of the 

 island groups in the Scotia Sea in one season (February -April 1968) have been interpreted by 

 some to demonstrate a four-year life cycle (Ivanov, 1970). 



With continuing efforts to determine the life span of this species. Mackintosh (1972) re- 

 evaluated earlier data, and with additional Discovery samples reiterated previous estimates of a 

 two-plus-year period to breeding. Thus, critical aspects of the biology and ecology of krill 

 remain to be clarified. These include: growth rates, longevity, fecundity; hydrographic features 

 of areas of high as well as low population densities and transport of eariy larval stages; pairing 

 and repeat spawning. These features of krill biology must be elucidated at diverse geographic 

 locations during every season and several annual cycles. The information derived will provide 

 the scientific basis for judgements concerning harvestable Umits. 



Changes in the abundance of krill is another aspect in which full information is lacking. 

 Though our present indirect methods have produced estimates of abundance or production 

 which may be adequate for purposes of harvesting, the variance in these estimates (considered 

 by some to be a factor of two or so) is so great that it is impossible to estimate the changes in 

 the abundance of krill which have occurred or may occur. While it is populariy believed that 

 krill stocks increased after whale stocks decreased, and there is indirect evidence that this 

 occurred, {eg, from increases in the populations of winged birds, penguins and seals that feed on 

 krill (Budd and Downes, 1969; Conroy, 1974)), direct evidence is lacking. Present techniques of 

 directly estimating krill biomass, from plankton net hauls, or by acoustic methods, are subject 

 to considerable variance because of the structure and highly irregular distribution of the 

 swarms. Such estimates may also be biased because, for example, of the escape of larger krill 

 from most nets, the fully unknown proportion of krill outside swarms and the lack of 

 information on the acoustic properties of krill, either individually or in swarms. 



Though these problems are of some significance, they do not invalidate present estimates 

 of biomass and productivity which have been presented as broad ranges. They do make it 

 difficult or impossible, however, to achieve the precision needed to monitor changes in the krill 

 population which might occur as a result either of a recovery of the whale stocks or of large 

 scale exploitation. The development of methods of monitoring changes in krill abundance is 

 highly desirable. Techniques that are under investigation and at the present stage show some 

 promise include refined acoustic methods from ships or buoys, aerial surveys and the use of 

 sateUites. 



