Trophia has been contracted by the New Zealand Ministry of Fisheries (MFish) to conduct a stock assessment for snapper (Pagrus auratus) in SNA 2, including estimating biomass and sustainable yields The specific objectives for this project include:

1.  To characterise the SNA 2 fishery and update the CPUE analyses for trawl fisheries in each area of SNA 2 using data up to the end of 2008-09 .

2. To conduct a stock assessment for snapper (Pagrus auratus) in SNA 2, including estimating biomass and sustainable yields.

The current stock assessment for SNA 2 is highly uncertain, largely due to the lack of a time series of relative abundance indices for the stock. This project will undertake a characterisation of the fishery and, thereby, identify any sectors of the fishery that may provide sufficient continuity to enable the generation of a time series of CPUE indices.

The development of a reliable CPUE index would substantially improve the power of the current stock assessment model. However, reservations remain regarding the potential of this project to generate reliable CPUE indices. Nonetheless, it is proposed to persist with the second objective of the project either with or without a CPUE time-series. The proposed age structured model provides the best approach to integrate the catch history and the time series of age frequency data. However, without a CPUE time series the model results would be highly dependent on assumptions relating to the fishery selectivity and natural mortality. In this case, it is proposed to test a range of scenarios relating to these variables to explore the plausible range of estimates of sustainable yield and relate these to the current level of catch.

The stock assessment modelling component of the project will be conducted using Stock Synthesis

This work is funded by MFish project SNA2009/01