Methods

Abstract

Most of the methods used have been presented in a separate methodological paper (Balon, 1972) and in the preliminary evaluation of Lake Kariba standing crops (Balon, 1973a). At the time of sampling, the indigenous fish stocks, except the eel, were distributed in 202 200 ha of inshore waters less than 20 m deep. This depth limit of the distribution was obtained by evaluating electroacoustic records and gill-net sets. The distribution of species within this area is largely unknown. The density of single species was obtained from quantitative samples in known blocked areas treated with fish eradicants (toxaphene, rotenone). Age determination was done by assessment of annuli from key scales and vertebrae; the growth was back-calculated for the previous growth seasons on the basis of empirical body-scale or body-vertebra relationships. The mean weights were interpolated from the weight-length plots on a double logarithmic scale, of which a more detailed explanation can be found in a special study (Balon, 1974b.

‘Density, growth, age structure, and harvest pressure are all interrelated, and the interactions and relationships have yet to be delineated in terms that have predictive value.’²