F-34 



are retained "by the net (or are of a size suitable for processing) none that enter the mouth 

 of the net will survive. Ilie effect of this is that unless trawls can be aimed at swanns 

 containing individuals of the desired size the fishery will be totally unselective as regards 

 size of krill caught. One of the objectives of management must clearly be to ensure that 

 sufficient individuals spawn to maintain the population. This implies that the fishery should 

 be based on the largest sized individuals in the population. 



The presently developing fishery is largely based on fishing at swarms identified on 

 echosounders. However at the moment it seems \inlikely that the presently developed acoustic 

 techniques can discriminate between large and small animals and unless there is shown to be 

 a requirement for processing to only use large individuals it seems unfikely that sufficient 

 funds will be channelled in this direction for developing the necessary teclmology. There 

 may be behavioural characteristics of krill which segregate adult and adolescent concentra- 

 tions; these would need to be identified by biological campling in -conjunction with the 

 "learning processes" that fishing captains would inevitably go throu^. It may also be 

 possible to regulate fishing to within areas that do not contribute to maintaining the 

 population (it has been suggested that South Georgia is such an area). 



Mention has already been made of the proposed use of remote sensing techniques for 

 estimating the standing stock of krill. The method depends on the identification of swairos 

 of krill either by satellite photography or acoustically and confirming the presence of 

 krill by field sampling. The identification of indications as being krill swarms is a 

 technological problem which can probably be solved. Hovjever, some caution should be exercised 

 in the interpretation of the results. 



Presently available information indicates that krill swanns are transient phenomena 

 depending for their formation on a variety of oxtomal causes one of which is probably food 

 availability. In addition it is not known vfhat proportion of the krill population at any 

 one time is present in sv/arms. 



On the assumption that food availability is a factor leading to sv/ann formation (the 

 more food, the more svjaims) it is arguable tliat consumption of krill (whether by prcdation 

 or fishing^ would increase the amount of krill in swaims, because the decreased grazing by 

 krill vrould tend to increase the relative food availability. The effect would be that obeer- 

 vations on the abundance or density of krill in swarms v;ould tend to underestimate the change 

 in total krill abundance as the season progresned. In ortler to overcome this problem it is 

 almost certainly necessary to gain information on the amount of krill not present in swanns 

 in relation to season, the presence of sv/arms and food and also environmental characteristics. 



6.10. Harvesting at higher trophic levels 



Duo to the supposed sensitivity of the Antarctic ecosystem it has been suggested that 

 a safer method of harvesting krill might be by harvesting krill consumers (either natxxral 

 or introduced) rather than krill. In this context natural consumers are generally considered 

 synonymous vjith whales although it could equally well apply to seals, fish or squid. From 

 the conservation viewpoint the utilization of krill via the vihalcs has several points in its 

 favour (e.g. exploitation of vjhales is now under international control, the catch limits are 

 based on scientific informc^tion that, if not as reliable as might be v/ished, is at least 

 much more reliable than that on krill, and the present resolve ty conservation pressure 

 groupr. in particular and scientists in general that overoxploitation should not recur) which 

 will buffer it against overexploitation. In the present situation it is more sensible to 

 consider the feasibility from all points of view of exploiting both krill and its consumers 

 and in this context the relative levels of exploitation would be considered in the context 

 of a multispocies fishery (Horwood, 1976). 



In a paper discussing the interactions between the North Sea fisheries for do.^ish and 

 herring (the herring being an important food or.^^anism of the do.gfish) Gulland (1970a) 



