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

Abstract

The Wilderness lakes system comprises three interconnected lakes; Rondevlei, Langvlei and Eilandvlei. The latter is further connected by the Serpentine channel to a lagoon at Wilderness. 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 Eilandvlei which serves as the system's major nursery area. Migration occurred mainly during the day and mostly towards high water. Fish communities throughout the system were sampled using seine and gill nets, and the Shannon-Weaver function used to described 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 Langviei which are furthest from the estuary mouth. Eilandvlei has an intermediate diversity with the Wilderness lagoon supporting the most diverse community. There is a lower diversity in Langvlei. The fish fauna of the Wilderness 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.