Patterns of distribution and abundance of fishes in different habitats of a mangrove-lined tropical estuary, as determined by fish trapping

Abstract

Spatial and temporal patterns of distribution and abundance of large, demersal fishes in the deep-water sections of Alligator Creek, in tropical northern Australia, were investigated. Small Antillean Z-style fish traps were utilized to compare different estuarine habitats along the navigable length of the creek. In particular, the traps were used to target the structurally heterogeneous 'snag' habitats provided by areas of submerged mangrove prop roots and fallen timbers in the deeper areas of the estuary.

During the study, 962 fish of 23 species from 15 families were trapped over 1128 trapping days, at an overall catch rate of 0.85 fish trap^-1 day^-1. Catches by numbers were dominated by two genera: Acanthopagrus (Sparidae) (51.8%) and Epinephelus (Serranidae) (20.3%). Of the 23 species trapped, eight had not been recorded during previous studies of Alligator Creek that used more conventional netting methods to target fishes in shallow parts of the estuary.

In trap catches, the total number of fish, the number of species, and the numbers of individuals of the most common species showed a general decline towards the upper areas of the estuary and generally were higher in 'snag' habitats than in areas lacking such structures. No clear pattern of temporal differences during the study was detected. Angling and seine-net catch data were used as independent indicators of spatial patterns of distribution and abundance for comparison with the patterns obtained from the catch data of traps. Data from all three sources demonstrated similar spatial patterns.