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93_SBW_09
Filename
93_SBW_09.pdf
Link to file
93_SBW_09.pdf (271.6 kb)
Abstract
In 2008, a preliminary assessment was carried out for the Bounty Platform stock. New abundance data were available from an industry acoustic survey of the Bounty Platform that indicated that there has been a very large increase in biomass in this stock since 2004. An attempt was made to fit this timeseries of industry acoustic data, along with a time series of Tangaroa acoustic surveys and catch-atage data, in a population model. Because of the poor fit to the acoustic data the model results are not reported here, but the Working Group did provide conservative estimates of biomass (section 4d) based only on the acoustic survey results to allow yield estimates (CAY) to be determined for the management of the fishery.
No new assessments are available for the Campbell Island and Pukaki Rise stocks. No assessment has been made of the Auckland Islands Shelf stock. The years given in this section of the report refer to the August-September spawning/fishing season.
Campbell Island stock
The 2007 stock assessment was not updated. For the base case, B2006 was estimated to be 78 000 t (90% credible interval 56,000–106,000 t), corresponding to 30%B0 (90% credible interval 20–41%).
The catch is dominated numerically by the strong 2001 and 2002 year classes, and the incoming 2004 year class also appears to be above average. The TACC was reduced to 20,000 t in 1 April 2006, and at this level of catch, the biomass is projected to remain stable over the next few years. At the current TACC level, the probability that the biomass will drop below B1991 is projected to rise to 3% by 2009 (Table 11). The assessment is much more optimistic than the equivalent stock assessment presented in 2006, particularly in the projections, as stock size is not predicted to decrease with future catches of 20,000 t (current TACC).
Bounty Platform stock
A survey carried out by the fishing industry in August 2007 indicated that there has been a very large increase in biomass in this stock since 2004. Catch-at-age data suggest that a strong year class (born in 2002) has recently entered the fishery. However, the stock assessment model was unable to reconcile the very large biomass increase with the series of observed catch-at-age data, and so estimates of the size of this year class and the current biomass are very uncertain.
The 2004 stock assessment estimated a virgin stock size of 86,000 t based on the mean recruitment estimated from 1988 to 2000. The range of estimates of biomass from the 2007 acoustic survey are above that level. The most conservative estimate is about 60% of the estimated virgin stock size and leads to the conclusion that the biomass of this stock is well aboveBMSY.
Without a formal stock assessment it is not possible to quantify the size of the SBW 6B stock and to determine a CAY for the fishery. However, conservative estimates of CAY were made by applying the reference fishing mortality to a conservative estimate of current vulnerable biomass based directly on the 2007 acoustic survey. The range of CAY was 15,000 to 20,000 t. The Working Group concluded that the risk that the biomass would drop below 20%B0 in 2008 would be negligible, if the TACC was based on these yield estimates. This advice was the basis for the TACC increase to 10,000 t from 1 April 2008.
Another survey in August 2008 confirmed that the 2002 year class is very strong and biomass was likely to be over 100,000 t.Using the results of the 2008 survey to estimate conservative estimates of CAY in a similar way to previously gave estimates of CAY of 13,500 t to 22,000 t. The TACC was increased from 1 April 2009 to 15.000 t.
Pukaki Rise stock
The assessment of this stock has not been updated since 2002. Recent catch levels (average 380 t since 2002) are unlikely to have made much impact on stock size. This stock has been only lightly exploited since 1993, and is likely to be above the level that will support the MAY.
Auckland Islands stock
No estimates of current biomass or yield are available. It is unknown if recent catches are sustainable or if they will allow the stock to move towards a size that will support the MSY. The only information available on stock size is from an acoustic survey in 1995.
Document date
Sunday, 31 May 2009
Document type
V 1.3
File format
Adobe PDF
File size
271.6 kb
Reference number
2009
Sort order
Uploaded from
M:\SCIPOL\Working Groups 2009\Plenary 2009\FINAL\MFish 2009 May Plenary\May 2009 - PDF\93_SBW_09.pdf
Uploaded date
Friday, 12 June 2009
Search tags
Species:
SBW;
Stock:
SBW1;
SBW6A;
SBW6B;
SBW6I;
SBW6R;
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