Recruitment, diversity and the influence of constrictions on the distribution of fishes in the Wilderness lakes system, South Africa

Abstract

The Wildemess lakes system (22°35'E/34°00'S) comprises three interconnected lakes; Rondevlei, Langvlel and Eilandvlei. The latter Is further connected by the Serpentine channel to a lagoon at Wildemess. The fish fauna is dominated by euryhaline marine species which migrate into the system as 0 + juveniles. During February 1984 it was calculated that 52 000 juvenile marine fishes migrated up the Serpentine towards Eilandvlel which serves as the system's major nursery area. Migration occurred mainly during the day and mostiy towards high water. Fish communities throughout the system were sampled using seine and gill nets, and the Shannon-Weaver function used to describe them in terms of diversity. The system can be divided into three areas on the basis of this function. The lowest diversity in numbers and biomass occurs In Rondevlei and Langvlei which are furthest from the estuary mouth. Eilandvlei has an intermediate diversity with the Wildemess lagoon supporting the most diverse community. Although Eilandvlel and Langvlei have similar environments, there is a lower diversity in Langvlei. This Is attributed 'to macrophyte encroachment and the shallow depth of the channel connecting these two lakes. In comparison with other South African coastal lake systems the fish fauna of the Wilde mess lakes system is species poor. This is partly a result of the shallowness of interconnecting channels, intermittent open mouth phase and low diversity of marine/estuarine fishes in adjacent coastal waters.

S. Afr. J. Zool. 1987,22(2)