Structure of a fish community in a temperate tidal mangrove creek in Botany Bay, New South Wales

Abstract

The fish assemblage in the lower reaches of a temperate tidal mangrove creek entering Botany Bay near Sydney, New South Wales, was sampled using rotenone every second month between December 1977 and October 1980. Almost 17 000 fish (weight ~ 115 kg), belonging to 46 species and 24 families, were collected. Six species dominated the assemblage and another four were relatively common. Fourteen species, including four of the above, were economically important. These fishes made up 38% of individuals and 32% of biomass and were represented only by small juveniles. Nineteen species (41%) were temporary residents; these mainly comprised juveniles of large species that live elsewhere as adults. Fifteen species (33%), most of which only attain a small size (< 100 mm), were assumed to be permanent residents. The remaining 12 species (26%) occurred in only one sample and were, therefore, classified as rare. The diversity (HI) and evenness (J') of the fish community were low and showed little seasonality because a few species dominated the assemblage on an irregular basis. Numbers of species and of individuals varied seasonally and were significantly correlated. Peaks in these parameters lagged behind those in water temperature by 4 months and were largely the result of the relatively restricted recruitment periods of several abundant temporary resident species. The large numbers of juveniles and small species in the mangrove creek habitat were attributed to the availability of suitable shelter and food for such small fishes. Concerted use of the mangrove habitat by several abundant temporary resident species during the same general period each year appeared to be facilitated by the occupation of otherwise vacant feeding niches and some staggering of their peak recruitment periods. Exclusive use of this habitat by small juveniles of several species in Botany Bay confirms that mangrove habitats in temperate Australia, like some of those studied in tropical and subtropical regions, are important nursery areas for fishes inhabiting adjacent estuarine and inshore marine habitats as adults.