Stock assessment of swordfish
Project: Stock assessment of swordfish
Project Code: SWO2004/01
Start Date: 1 October 2004
Completion Date: 30 September 2005
Vessel Use: None
To conduct a stock assessment for swordfish (Xiphias gladius), including estimating biomass and sustainable yields.
To update the descriptive analysis of the commercial catch and effort data for swordfish from the longline fisheries with the inclusion of data up to the end of the 2003/04 fishing year.
To analyse length frequency, sex ratio, and reproductive condition data for swordfish collected by the Observer Programme and other sources during the 2003/04 fishing year for input into stock assessment models.
To review and summarise the historical biological data (including length frequency, sex ratio, otoliths, and reproductive condition data) for swordfish collected by the MFish Observer Programme and other sources since the start of these programmes and the use of these data as inputs into stock assessments.
To update the unstandardised and standardised catch per unit effort analyses with the inclusion of data up to the end of the 2003/04 fishing year.
To conduct a stock assessment, including estimating biomass and sustainable yields for the SWO.
The Pelagic Fisheries Stock Assessment Working Group will review the outputs of project SWO2003/01 prior to the specific objectives for this project being finalised. That review will also incorporate the latest available Australian research into swordfish stock status.
What is the stock status of swordfish in the southwest Pacific Ocean? Various approaches have been used successfully to assess swordfish stocks in other oceans. Such approaches and recent work on CPUE standardisation in the region should be able to answer questions about current exploitation relative to maximum sustainable yield.
At present longline catches of swordfish are increasing in Australian and New Zealand waters as they are more broadly throughout the Pacific Ocean. While New Zealand longline catches of swordfish are about half those of Australia, concern about sustainability has been voiced locally by the recreational fishing sector. Australia is currently developing an operating model for the south west Pacific Ocean using Australian, New Zealand and Japanese longline data that will allow Australian fisheries managers to test the effect of different management strategies (e.g. the effect of various catch allocations on stock dynamics). This will be ultimately be an important tool for addressing the issue of sustainability under different catch limits but depends on data that is not generally available outside of the New Zealand and Australian EEZs. In particular, size composition of the swordfish catch is not available for most of the southwestern Pacific and indeed is poorly sampled for much of the history of the New Zealand and Australian fisheries. The Australian model also incorporates conventional tagging data that are likely to yield uncertain parameter estimates in the short term. New Zealand has been cooperating with Australia in their efforts to develop the operating model and can expect to be able to utilise this model when it is finished.
Swordfish catches are significant to New Zealand and an independent stock assessment will be useful in the management for this species. Swordfish are recognised as a highly migratory species. Within this context, this research project is considered a high priority.
Objectives 1, 2, 3 & 4
Observers have collected a volume of material describing SWO catches in the last 15 years. The standardised CPUE analysis for SWO developed in SWO2003/01 should be updated with the latest years data. This work will draw on the outputs of project TUN2003/02 and should not repeat research undertaken as a part of that programme.
This modelling should be geared to data that are generally available and hence implies a model that is not dependant on data types that are only available for portions of the fishery. Fine scale catch and effort are available for the within zone catches in New Zealand and Australia, however, for much of the rest of the SW Pacific, the data are only available in 5 x 5 degree blocks.
There are several reasons for New Zealand to conduct a stock assessment for southwestern Pacific swordfish including: when swordfish is brought into the QMS, the TAC derived for New Zealand should be explicitly linked to maximum sustainable yield for the stock; this modelling work will supplement modelling work being done by Australia and provide an independent check on the results they generate; estimates are needed of a range of parameters of direct interest to management of this stock in addition to MSY and hence enable New Zealand to meet its international obligations with respect to swordfish; and, once developed this modelling approach can be applied to other highly migratory fish stocks.
This project forms a part of the programme to provide the information on sustainable yields and stock status required for the sustainable utilisation of New Zealand’s fisheries resources, a part of the swordfish medium-term research plan and a part of the pelagic fisheries medium term research plan. This project is consistent with the Ministry of Fisheries Strategic Research Directions document.
Cost Recovery Information:
The percentage allocation for this project will be attributed to the following Fishstocks according to rule 9.2 of the Fisheries (Cost Recovery) Rules 2001:
The project is estimated to cost between $50,000 - $100,000.