Aspects of the ecology and exploitation of the fishes of the Kosi Bay system, KwaZulu, South Africa.

Abstract

ln this study the exploitation of the fish fauna of the Kosi

estuarine system by man and natural predators is described

and estimates made of the off-take and its species

composition. The most important human exploitation, that by

the traditional Zulu fish traps, was monitored over a four

year period and the data collected were used to give an

insight into the marine fish populations of the system.

All the physical parameters, which it was thought could

influence the migrations of fish, were monitored and

correlations between these and the daily and monthly fish

trap catches were used to interpret fish movements into and

out of the system. Reasons for the annual migrations and day

to day movements of fish were investigated.

In order to establish relative off-takes by local fishermen

and sport anglers fish were tagged inside the system and the

recovery rates by the various fishing methods were used to

calculate estimates of the percentage off-takes of these

principal human exploitation methods. These data were also

used to obtain estimates of the population sizes of the major

marine fish species inside the system. Catch data were used

to indicate the levels of estuarine dependence of these

species. Where possible comparable data from other areas were

used to indicate whether or not similar trends in catch

abundance were obvious. The ecological and economic importance of the Kosi system

is discussed and its value to the local inhabitants stressed.

Competition between the various fishing techniques is

described and recommendations are made concerning future

fish exploitation. Natural predation rates are also discussed

and levels compared with those of other systems.

The fish food resources of the systems are considered in the

light of recently declining salinities, destruction of swamp

forests and increasing numbers of hippopotami. The

implications of these changing factors are discussed as is

their impact on the Kosi Bay fisheries.