Life history strategy and population characteristics of an unexploited riverine cyprinid, Labeo capensis, in the largest impoundment in the Orange River Basin

Abstract

The life history of an endemic riverine African cyprinid, Labeo capensis, that dominates the larger ichthyofauna in a large impoundment in the Orange River Basin four decades after damming, was investigated. Both sexes grew at a similar rate until the onset of  aturation, after which male growth and survival rates declined. Male mortality rate was significantly higher than estimated for females explaining both the older ages attained by females (12 years) compared to males (9 years) and a female-dominated adult population. Maturation proceeded faster in males than in females, but was considerably delayed in both age and length. Female reproductive contribution was double that of males despite males maturing a year earlier. Intraspecific life history comparisons with riverine and early impoundment populations suggest that L. capensis has largely maintained its riverine life history characteristics. These characteristics are common in large fishes that are well-adapted to seasonal riverine environments, but often show high vulnerability to damming or overfishing. The absence of a directed fishery and the availability of periodic floodplains that form when marginal vegetation is inundated by either the unregulated inflow of the Orange River or local erratic rains is suggested to have played a vital role for the successful establishment of L. capensis within the impoundment.

Key words: age and growth, reproductive biology, periodic strategist, mortality, gillnet
selectivity, population structure.