ABSTRACT: Epinephelus coioides and E. malabaricus are closely related species of serranid fishes. They are similar in appearance, occupy the same habitats and are represented in estuaries of northeastern tropical Australia almost entirely by juveniles. Fish traps were used to sample these 2 species from 3 estuaries on the northeast coast of tropical Australia over a 2 yr period. Patterns of distribution, abundance and size structure were compared. Despite the similarities between the 2 species, they showed quite different patterns of distribution and abundance, both within and between estuaries. In seaward parts of the estuaries the numbers of E. coioides were similar to or greater than those of E. malabaricus. However, in upstream areas E. malabaricus became much more abundant than E. coioides. The reasons for this change in dominance are unknown. However, upstream areas of the estuaries exhibited extreme levels of salinity (either hypersaline or hyposaline) and catches of the 2 species correlated with the maximum deviation in salinity. This suggests that if salinity, or some correlated variable, does influence the abundance of the 2 species, it is through long-term effects rather than short-term changes. Regardless of the reason, these spatial differences in abundance suggest that E. malabaricus is better equipped to deal with the challenges of estuary life than is E. coioides.

KEY WORDS: Estuary . Tropical . Fish distribution . Salinity

Published in MEPS Vol. 137 (1996) on June 27
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996