Influence of fishery effort and damming on Kafue River, Zambia fishery production

Background/Question/Methods

To support sustainable fisheries production in regulated rivers, many recent efforts have focused on mimicking pre-regulation flows. More natural flood regimes are expected to increase biological production via increased seasonal spawning habitat and allochthonous nutrient inputs. To explore the possible benefits of improving environmental flows in a tropical floodplain fishery on the Kafue River, Zambia, we modeled past and current catch per unit effort as a function of flood regime and fishing harvest before and after hydropower dam construction. The fishery consists largely of Cichlidea, Clariidea, and Cyprinidae. We hypothesized that the post-dam flood regime reduced fish abundance and that mimicking natural flows would increase production. Thus modeling results might guide any future enhancement of environmental flows. Specifically, for the years 1955 to 1996, we related catch per unit effort to total fisheries harvest, a multivariate index of yearly water regime, and catch per unit effort in previous years (as an index of density dependence). The water regime index was derived from a canoncial correlation of mean monthly flow before and after dam construction in 1976. We used maximum likelihood estimation and Schwarz information criterion to select among likely models.

Results/Conclusions

For the pre-dam era the most likely model included terms for density dependence and total harvest in the previous year, but no terms for flood regime. For the whole time series, the most parsimonious models explaining catch per unit effort also did not contain terms associated with flood regime but did include density dependence and/or total harvest. These models suggest that fishing effort is the principle driver of the observed patterns in catches during the modeled period both before and after dam construction. High fishing pressure may prevent fish abundance from responding measurably to changes in flood regime on the Kafue River. Under the current model, it appears that changes in dam operation allowing for environmental flows would be neither beneficial nor harmful for fishers and the limited resources of fishery managers may be more usefully used to mitigate fishing effort.