Patterns of movement of some fishes within an estuary in Tropical Australia

Abstract

The movements of fishes marked, released and recaptured during a fish trapping study in the estuary of Alligator Creek in tropical north-eastern Australia were studied over a period of two and a half years. The ability to place fish traps accurately with respect to landmarks enabled movements as short as 40 m to be detected. For each of six species of fish, more than 10 individuals were recaptured in Alligator Creek. Within these species, 258 of 1164 tagged fish were recaptured. Three patterns of movement were apparent. The serranids Epinephelus coioides and E. malabaricus and the lutjanid Lutjanus russelli tended to move little, usually being recaptured within 40 m of the site of release. The sparids Acanthopagrus australis and A. berda moved more extensively but still tended to remain within a few hundred metres for extended periods. All the above species demonstrated a strong tendency to be recaptured on the side of the creek on which they were initially captured. The tetraodontid Arothron manilensis proved to be much more vagile than did the other species, ranging freely over relatively large areas of the estuary and often crossing to the opposite bank of the creek. No species showed any preferred direction of movement or any tendency for increased displacement from the site of release with increased time at liberty.