It is over 10 years since the original model design, which was conditioned on Commonwealth logbook data over 2001 – 2005, was introduced and much has changed in the SESSF over this period, such as marked changes to the fishing fleet resulting from government buy-outs during 2006 and potential climate change on fisheries and fish distribution, particularly in south-east Australia. This approach may now be outdated by potential changes to the relative abundance of different SESSF species and changes in species behaviour. In an effort to find efficiencies in the sampling design, it is timely to re-examine underlying model assumptions (e.g., depth preference, day-night preference, and species range limits). This will provide updated model-based CVs using more recent Commonwealth logbook data, and should provide more reliable fishery independent abundance indices for selected SESSF species.
The FIS was originally intended to support management of SESSF species, providing an abundance series that is free of the influence of fisher behaviour, market forces, closed areas, management regulations and changes in gear used. Given the investment by the fishing industry and Government in the five completed surveys over the last 10 years, it is appropriate to consider how FIS abundance indices can be used as an input to manage the SESSF. To date, these indices have been incorporated in Tier 1 stock assessments for only three species, where it does not appear to be influential. It is not clear how these estimates could be used for non-Tier 1 species.
Final report
Implications 1: Station re-examination
The framework developed could assist with any future refinements to the FIS design. The set of candidate stations is dependent on the species chosen, so a different set of key species would produce a different set of candidate stations for relocation.
Software was updated. The reconditioning analyses led to a reduction in the CVs, increasing the utility and confidence in the FIS2 results.
Large variation was observed in possible trends from simulations using the calculated CVs for the five survey abundance estimates. Simulation analyses suggest that process error should be explicitly considered, as sampling error alone could not produce such variable results.
Differences in seasonal patterns between years were accounted for which led to a further reduction in both abundance CVs and inter-survey variability, hence increasing the utility of the FIS3 results.
Due to the relative length of the FIS abundance series compared to other data sources, the FIS series is likely to be too short to adequately assess the impact on stock assessment results in most scenarios explored.
