The assessment of exploited Antarctic fish stocks
Comments on the status of exploited fish stocks in Antarctica are provided in the context of assessing the methodology used by Kock et al (1984). Attention is drawn to the problems of interpreting the management guidelines of Article II of the Convention for the Conservation of Antarctic Marine Living Resources, that is to ensure that stocks should not fall below the level at which their net productivity is at maximum. The yield per recruit relationship may be viewed as a possible indicator of net productivity. However, attempts to manage on the basis of this relationship have an associated risk of recruitment decline. Some possible solutions to this problem are considered including the Kock et al (1984) approach to adopt Fo.1 as a target fishing mortality. The stochastic nature of recruitment makes the problem more complicated. In general all of these imply the need for a conservative management policy aimed at ensuring stable recruitment.
The usage of catch per day fishing as unit of CPUE adopted by Kock et al (1984) is discussed. Catch per fishing hour is more likely to reflect the changes in stock abundance than catch per day. Separate analyses of CPUE by target species would be more desirable.
Certain results of the Kock et al analyses seem clear regardless of whatever methodology might be used. The biomasses of the spawning stocks of several species, particularly Notothenia rossii, Dissostichus eleginoides and Pseudochaenichthys georgianus, have been reduced to levels where their stable recruitment must be in doubt. The status of the nototheniids gives most cause for concern, as Kock et al report on a number of studies which indicate that there is a substantial by-catch of juvenile nototheniids taken in the krill fishery around South Georgia.
Accordingly it is clearly necessary on the basis of available evidence to consider the immediate adoption of conservation measures for certain stocks in the convention area.