Walsh, C.T., 2003. Sex-related differences in distribution, age and growth of Australian longfinned river eels (Anguilla reinhardtii) in coastal catchments of south-eastern Australia. Masters thesis. University of Technology, Sydney, Australia.

Summary

Sex-related population and life history characteristics of Longfinned river eels (Anguilla reinhardtii) were examined among different riverine sections (zones) from three coastal catchments (Hacking, Hawkesbury and Clarence Rivers) in NSW, southeastern Australia. The size range of A. reinhardtii at sexual differentiation and migration were comparatively larger, with these eels having less developed gonads during the initial phase of their spawning migration, than for most other anguillids world-wide. Females were generally larger and older than males and were captured in relatively higher proportions throughout the catchments, while males were predominantly caught in brackish upper tidal areas. The recapture rate of tagged eels was high (19%), and recaptured eels indicated a high degree of site fidelity. Mean annual growth rates of A. reinhardtii showed high variability, even within the same sex at similar sites. Young female eels displayed the highest growth rates, with their overall growth being significantly faster in the tidal areas than in non-tidal freshwater areas. Similar to other anguillids, A. reinhardtii exhibits a high degree of sexual dimorphism. Males develop and mature rapidly, possibly using a time-minimising life history strategy, while females live longer and grow larger, which may maximise their fecundity. This dimorphic strategy arises from differences in the timing and levels of physiological development at different life history stages in both males and females. Environmental factors such as habitat preference, food availability, population density and fishing pressure may also influence these physiological processes and caused high intra- and inter-population variability in population characteristics within the sexes. Current fisheries legislation prohibiting commercial eel fishing in flowing non-tidal waters in NSW should be maintained in order to provide a refuge for future female spawning stocks. An increase in the minimum legal size at capture (currently 30cm) to 58cm is recommended to help conserve male spawning stocks, which reside primarily in tidal waters where commercial fishing activity is focused.