Sampling estuarine fish species for stock assessments
NSW Department Of Primary Industries
Charles A. Gray
1. To investigate standard methods for independently sampling fish stocks in estuaries
2. To determine adequate ample sizes for providing the breakdown of the age and sex composition of the major esturine fish species
3. To determine the variability in age, length at age and sex composition of commercial catches of the main estuarine fish species at the major landing locations along the NSW Coast over a two year period
4. Determine the variability in age and sex composition between ocean caught and estuarine caught fish
5. Determine and begin implementation of an efficient log book system of individual fishers at these locations
6. Advise industry on the means of assessing estuarine fish stocks
Estuarine fishes in NSW are exploited by commercial and recreational fishers and are subject to significant pressure from habitat degradation. The NSW commercial estuarine finfish fishery is highly complex as it is based on multi-species and many fishers using variety of methods. Furthermore, there is very little biological information on which to assess the status of these stocks. Four key species were identified for investigation: yellowfm bream (Acanthopagrns australis), sand whiting (Sillago ciliatd), dusky flathead (Platycephalus fuscus), and luderick (Girella tricnspidata).
Sampling of young (recently settled) juvenile fishes was used to assess recruitment variability in estuarine fishes. Quantitative sampling across several estuaries identified latitudinal gradients in the timing of recruitment of sand whiting, bream and luderick to estuarine habitats. The relative abundance of young fish varied greatly among sites within an estuary as well as between estuaries. Future sampling of juvenile fishes to obtain indices of recruitment would need to be done over extended periods of time and across many locations within an estuary and estuaries and would therefore be relatively costly.
Keywords: Estuarine fish, stock assessment, recruitment, size and age structure, log book, Sparidae, Sillaginidae, Platycephalidae, Girellidae