Snapper population modelling and stock assessment
Project: Snapper population modelling and stock assessment
Project Code: SNA2004/01
Start Date: 1 October 2004
Completion Date: 30 September 2005
Vessel Use: None
Overall Objectives:
- To carry out stock assessment of snapper (Pagrus auratus), including estimating biomass and sustainable yields.
Specific Objectives:
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To update the CPUE analyses for longline fisheries in each area of SNA 1 and develop a single trawl index for Bay of Plenty using data up to the end of 2003/04.
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To update the stock assessment for the Hauraki Gulf and Bay of Plenty snapper stocks using a spatially explicit model incorporating seasonal fisheries and movement.
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To update the assessment of SNA 8.
Rationale:
General
The snapper fishery is New Zealand’s largest inshore finfish fishery by value. SNA 1 is the largest snapper fishery with a current TACC of 4500 t out of the total snapper TACC for all areas combined of 6494 t. SNA 8 is the second largest snapper fishery with a current TACC of 1500 t. Snapper also form important fisheries for recreational fishers and Maori, but the annual catch is not known reliably.
The stock assessments for snapper mainly rely on the absolute abundance estimates from tagging programmes. In 2004 the preliminary results from the SNA 8 tagging programme will be available for input to the assessment. In other stocks the recent abundance is monitored by CPUE indices from the main commercial fisheries. Yearly recruitment indices are also estimated using trawl survey indices and catch at age data sampled from the commercial fisheries.
Objective 1
Standardised CPUE analyses should be updated for each area in SNA 1 using data up to the end of 2003/04. The CPUE of the single trawl fishery in the Bay of Plenty should also be analysed as this is the dominant method in this area.
Objective 2 The Hauraki Gulf and Bay of Plenty snapper are currently assessed as one stock, with the assumptions of common growth rates, recruitment patterns and fishing mortality. However, it is apparent from catch sampling of the longline fisheries that age composition and fishing mortality rates vary between the two areas. The results from previous tagging programmes should be used to model the seasonal movement of snapper between these two sub-stocks.
Objective 3
The stock assessment of SNA 8 will be carried out in 2004 using the provisional results from the tagging programme. An updated assessment should be completed in 2005 including new catch at age data from project SNA2003/03 and the final results from the tagging programme.
Strategic Relevance
All the objectives in this project are consistent with the Fisheries Resources goal in the Ministry of Fisheries Strategic Research Directions document.
Cost Recovery Information:
The percentage allocation for this project (based on an assessment of research effort according to rule 9.2 of the Fisheries (Cost Recovery) Rules 2001) is as follows:
The project is estimated to cost between $250,000 — $300,000.