The orange roughy fishery remains the most valuable component of the South-East Fishery (SEF). Following a series of egg and acoustic surveys of the spawning stock off St. Helens, Tasmania from 1990-1993, and an international review in 1994, it was concluded that the fish-down of the stock had been completed and SETMAC adopted a TAC that would enable the stock to rebuild to 30% Bo by 2004. However, following data reanalysis and increasing emphasis on the combined stock hypothesis in the 1996 and the 1997 assessments, it appears that TACs would need to be further reduced to enable the stock to rebuild to 30%Bo by 2004. This would be a major loss of revenue to industry. The validity of the current estimates of stock status therefore need to be clarified.

To clarify the status of the stock a survey of St Helens hill was requested that had greater spatial and temporal coverage than in previous years. In addition, there is an ongoing need to develop deepwater acoustic assessment techniques for orange roughy stock assessment using both industry vessels and research vessels. To carry this out in a cost effective manner, information from fishing vessel sounders will be collected over a four week period in conjunction to the precise CSIRO deep-towed multi-frequency acoustic surveys over the height of the spawning period. During the intensive survey we will cross calibrate the various acoustic platforms to assess how best to use industry acoustics in the long term management of the resource.

It is not known why orange roughy spawn at St Helens Hill with such regularity and part of this study will be to establish both the water column and seabed attributes at both the St Helens and St Patricks Head grounds.

A large fishery for orange roughy on the South Tasman Rise (which straddles the Australian EEZ and International waters) developed strongly in 1997. As part of our voyage we will survey the main spawning hill at the time of anticipated peak spawning to obtain an initial indication of stock size.

The vessel will operate off the eastcoast of Tasmania on a seamount known as St. Helens Hill 41:14S 148:45.5E and associated fishing grounds. Over a two week period the vessel will conduct three echo integration acoustic surveys of the hill and associated fishing grounds using multi-frequency techniques. These surveys would provide species composition, biomass and school dynamics information. In between the acoustic surveys detailed multi-frequency in-situ target strength measurements will be performed to obtain both target strength and species composition information. Species identification will be validated with catches obtained from a MIDOC opening and closing pelagic trawl form the vessel. Demersal trawling on deep-water marks at the base of the hill will be performed by a commercial vessel. CTD measurements will be taken continuously with the towed body as it is being towed, as well as dedicated vertical CTD drops to measure sound speed and absorption.

The benthic habitat of the fishing grounds will be assessed from samples taken with the benthic sled, and digital video system. Mapping of the seabed will also be undertaken with the deep-water acoustic towed system.

If available the ADCP will be used to measure currents at the hill and underway to investigate the current field around the fishing ground as well as long term trends.

On the 28^th of July we will leave the St Helens Hill area and steam to the South Tasman Rise (approx 47 20:0 S 149 00:0 E) to perform an acoustic survey of a known spawning aggregation.

To obtain trace metal (pCu and pCd) profiles from the jarosite dumping site using newly developed in situ Ion Selective Electrodes (ISE) which will be attached to the CTD rosette for deployment. These ISE profiles will be calibrated by discrete trace metal samples taken from the same cast using Helmond Byrne bottles and standard trace metal collection techniques. The12 calibration sample bottles will be packed in transport boxes and transferred to the sharkcat in Port Arthur (along with the ISE system) for return to the CSIRO in Hobart for subsequent sampling and processing under clean conditions.(Denis Mackey)

If available underway ADCP data will be recorded (George Cresswell).

Equipment required from Vessel

CTD, MIDOC net, benthic sled, logging system and DGPS.

Deepwater pole operational, Sonar system, Positioning system mounted in moon pool

Vessel motion dynamics from Ashtec GPS and pitch roll monitors

If available the underway ADCP will be operated

Simrad EK500, Deep water towed system and winch, video-camera system.

Special requirements eg: Space, power accessibility etc

Winch system on back deck

Deep–water positioning system