SILVER WAREHOU – DRESSED (swa DRE)

Executive Summary

1. MFish recommends that consideration be given to decreasing the conversion factor (CF) for silver warehou (SWA) in the dressed (DRE) state from 1.70 to 1.65.
2. This recommendation is based on analysis of a large amount of Scientific Observer sampling data, well spread over the geographical and temporal range of the target trawl fisheries where silver warehou is taken as bycatch, with particular emphasis on New Zealand vessels in the Chatham Rise, west coast South Island, and Stewart-Snares Shelf. There can be a reasonable level of confidence associated with the estimate produced.

Background

3. This paper reviews the CF from greenweight to the ‘dressed’ (DRE) state for silver warehou (SWA) (Seriolella punctata). The current CF for this state is 1.70.
4. The state is defined in the Fisheries(Conversion Factors) Notice 2005 in relation to all species of finfish not separately defined, as the body of a fish from which the head and gut have been removed with:
   1. The anterior cut being a continuous straight line passing immediately behind the posterior insertions of both pectoral fins;
   2. The forward angle of the anterior cut not less than 90 degrees in relation to the longitudinal axis of the fish;
   3. No part of the tail cut shall be forward of the posterior base of either the hindmost dorsal fin or the hindmost anal fin, whichever is nearer the caudal fin; and
   4. The belly flap, either intact or divided along the ventral midline.
      
5. The CF for ‘trunked or dressed’ SWA was first introduced on 1 October 1986, and was set at 1.70. The state was renamed ‘dressed’ and revised down to 1.60 on 1 October 1990. The CF for SWA DRE was slightly increased to 1.65 on 1 October 1995. It was returned to the original value of 1.70 on 1 October 2000, where it has remained without review since that date.
6. The Scientific Observer Programme sampled 9.75tonnes greenweight of this state in the 2002 calendar year: 3.16tonnes in 2003; 10.68 tonnes in 2004; and 5.82 tonnes in 2005.

Rationale for Management Option

7. The DRE state accounts for almost all of the total landings of silver warehou, but a small amount of fish is landed green. These levels have remained constant over the years 2003–2005.
8. SWA DRE was landed mainly by New Zealand registered vessels in 2003–2005, with only a few percent attributed to vessels registered in other nations, i.e., Korea, Japan and the Ukraine. The Scientific Observer CF sampling was therefore appropriately distributed amongst vessel nationalities, with most of the sampling taking place on New Zealand vessels and a small amount on Korean vessels.
9. Landings of SWA DRE were spread throughout the2003–2005 period. Comparatively little sampling occurred during winter (April-July) 2003, (May-June) 2004, but sampling was well spread in 2005.
10. Samples of this state have been collected in every year since the state was renamed and revised in 1992, and the annual unweighted CFs have ranged from 1.59 to 1.70 (rounded) with an overall CF of 1.66. There is no indication of a trend in the CF overtime.
11. The analysis is based on a large amount of sampling data well spread over the geographical and temporal range of the target trawl fisheries where silver warehou is taken as bycatch,with particular emphasis on New Zealand vessels in the Chatham Rise,west coast South Island, and Stewart-Snares Shelf. There can be a reasonable level of confidence associated with the estimate produced. Analysis of variance tests showed that the greatest significant difference in CFs was by month, so CFs was weighted accordingly. The month weighted CF for SWA DRE (rounded to the nearest 0.05) is 1.65.

Preliminary Recommendation

12. MFish recommends that the CF for the ‘dressed’ state of silver warehou be decreased from 1.70 to 1.65.