Since the 2005 Plenary report was published, an update of only the sub-Antarctic assessment in 2008

has been reported in this document series. Other assessments have been completed, but either were

not markedly different to the results already reported, or were not considered sufficiently more

reliable to justify their inclusion. In addition, refinements to the hake model structure are still being

investigated. The stock assessments reported here for the Chatham Rise and west coast South Island

stocks were carried out in 2004. For the purposes of stock assessment modelling, the Chatham Rise

stock was considered to include the whole of the Chatham Rise (including the western end currently

forming part of the HAK 1 management area). The sub-Antarctic stock was considered to contain

hake in the Southland and sub-Antarctic management areas; although fisheries management areas

around the North Island are also included in HAK 1, catches of hake in these areas are very small.

Sub-Antarctic stock (HAK 1, excluding the Chatham Rise)

Although estimates of current and reference spawning stock biomass may not be reliable, it is likely

that the current TACC is sustainable, as current catches do not appear to be having a marked impact

on biomass levels. Absolute biomass is probably large relative to catches, and recent declines in

biomass are largely due to recent levels of poor recruitment (see Figure 1).

Chatham Rise stock (HAK 4 and western Chatham Rise HAK 1)

Since the assessment completed in 2004 there have been changes in the pattern of this fishery (see

section 6 above) and changes in the model structure (see section 4.2.7). The Working Group did not

finalise an updated model for the 2006–07 fishing year that adequately addressed all the issues raised.

The 2004 model results suggested a decline in biomass, with biomass in 2004 at about 35% B

0.0 in 2009 to be 88% with catches of 3616 t, and 28% with catches of 1800 t. The higher assumed

West coast South Island stock (HAK 7)

An attempt was made in 2004 to determine the stock status of this stock by inclusion of all the

available data in a Bayesian assessment model. The assessment suffers from a lack of an independent

abundance index for the stock. Hence these results should be treated with caution.

The model was fitted to catch at age data from the commercial fishery with the catch history and

biological parameters (including

varied to determine the sensitivity of the model results to the catch at age data. In the initial case the

logistic assumption for the selectivity ogives is considered a conservative assumption. This run

suggested current biomass was between 30% and 70% B

biomass and stock status. All the model results indicated that current catches appear to be sustainable

in the short term.

[Subsequent assessments, although not reported in the Plenary document, have not been at odds with

this result.] Year class strengths from 1995 to 2000 are estimated to be weaker than average. In the

projections, the model assumes average year class strength since 2001, although more small hake

have been caught in the most recent trawl surveys, suggesting that the 2002 year class may be above

average. Projections for the Chatham Rise stock estimated the risk of reducing the stock below 20%

B

catch of 3616 t represents the current HAK 4 TACC plus half the HAK 1 TACC, while the lower

catch level of 1800 t represents the HAK 4 TACC only (see section 4.1.1).