An extensive winter survey indicates that orange roughy stocks on the Chatham Rise are in good health.

A rare day of calm out on the Chatham Rise. (photo: Tim Ryan)

Tim Pankhurst, Seafood Magazine, December 2022

A successful acoustic and biological survey programme of the Northwest and Northeast Chatham Rise orange roughy (ORH) spawning stocks was carried out on Sanford’s San Waitaki during a 30-day voyage from mid-June to mid-July.

Orange roughy migrate to both underwater features and flat grounds to spawn in late June, or early July. For most of the year, the fish are dispersed over a wide area at lower densities. It is only during spawning that the roughy form densely packed schools that make them suitable for acoustic surveys. These surveys provide snapshot biomass estimates of the spawning population that form a key input into the stock assessment process and the subsequent setting of quota.

The dual objectives of the commercial and scientific voyage were for the vessel to fill up and for a credible scientific survey programme to be completed. Surveying was carried out mainly during vessel downtime while fish were being processed and dedicated charter time was used where survey operations delayed normal fishing operations.

Ongoing cooperation between scientists and bridge officers during the voyage meant that San Waitaki was able to meet its catch target without compromising the survey program, according to the voyage report.

Acoustic Optical System (AOS) surveys were completed on Morgue and Graveyard hills in the northwest, and at Rekohu, Spawn Plume and Mt Muck to the northeast. These were complemented by vessel acoustic surveys. Each location received sufficient survey effort to provide a good understanding of the spawning stock.

Some minor technical issues were resolved early in the survey and recording of high-quality AOS and vessel-based acoustic data was achieved for the duration of the survey program. Biomass estimates will be forthcoming for all locations.

The key observations were:

  • A very large aggregation of orange roughy observed on all sides of the Morgue extinct volcanic feature
  • Graveyard held only a small amount of roughy, as was found in 2013 and 2016.
  • Substantial aggregations across a reasonably large area at Rekohu but biomass did not appear to be as large as in previous years. Rekohu received a lot of survey effort as the aggregations were very mobile and never really settled as spawning progressed (as we had seen in 2013 and 2016), hence surveying was quite challenging.
  • The Spawn Plume aggregation was also quite mobile but less so than Rekohu and good aggregations were surveyed.
  • Good aggregations were seen on Mt Muck. Previous surveys observed high aggregation variability over 24-hour cycles, so it was pleasing to achieve two AOS surveys during periods when good aggregations of orange roughy were present.

The biological sampling program covered all catches during the voyage and served to comprehensively monitor the build-up to the spawn and achieved or surpassed the number of otolith samples required to be collected as a basis for age-structure determination from each of the survey locations.

Sampling of orange roughy included recording of individual standard lengths, weights, sex and spawning condition from samples of 100 fish and collection of otoliths from 25 – 100 fish, with a target of 500 otolith samples from each surveyed aggregation. Bycatch species composition was determined by weight and number of individuals per species and lengths were recorded for abundant species.

Trials of the Seafloor Monitoring Automated Recording of Trawl Camera (SMART-Cam) were carried out. Automated operation with seamless transfer of images from trawl deck to bridge was successful. Image quality was good when the trawl headline was close to the seafloor. The trials provided an understanding of what adjustments are needed to improve image quality at higher headline heights.

The Sealord AOS was the primary survey tool for estimating biomass, using echo integration methods. It consisted of a sled-style platform attached to the headline of the vessel’s demersal trawl net. This system was built as a collaborative project involving Sealord and CSIRO starting in 2012.  For this survey, the AOS housed a two-frequency acoustic system (38 and 120 kHz) based on Simrad ES60 transceivers. The system was battery-powered with all data logged to internal storage media.

The voyage was considered a complete success with each of the priority spawning locations receiving comprehensive survey coverage that was well-timed with respect to the peak spawning period, and with the vessel meeting its catch objective of 600 tonnes. San Waitaki has excellent seakeeping capability and is acoustically quiet, providing high-quality acoustics from the hull sounder in all but the worst of weather conditions.

CSIRO voyage leader Tim Ryan thanked Sanford general manager fishing Colin Williams and deepwater fleet manager Darryn Shaw for their support of the survey.

“The voyage was a huge success,” he said.  “Our surveys involved deploying sophisticated acoustic and camera instruments, using these to conduct transect lines across the orange roughy aggregations. This required a high level of skill from the ship’s officers and crew. To their credit, they remained committed to the task even when at times catch rates were being affected. Importantly both survey and catch objectives were achieved through close cooperation between all parties.

Rear deck of San Waitaki looking aft. CSIRO’s new modular AOS is in the net awaiting deployment. The system is attached to the headline of the trawl net. A set of 16 floats is attached to provide the buoyancy needed to ensure that the heavy AOS does not affect the operation of the net when fishing. (photo: Tim Ryan)

“San Waitaki proved to be an excellent platform and it was a pleasure to work with Captain Tom Jackman, 1st Mate Deon Hatfield and indeed the entire ship’s complement. The success of this voyage will help ensure sustainable harvest of the Chatham Rise orange roughy into the future.”

The survey was commissioned by the Deepwater Group and funded by ORH 3B quota owners. Biological sampling and survey management were completed by Rob Tilney of Thalassa Fisheries Support. The survey results will be presented to a meeting of Fisheries New Zealand’s Deep Water Working Group this month for review and acceptance after which they will be used in updated stock assessments of the two Chatham Rise stocks in early 2023. This survey model allows biomass surveys to be conducted at a marginal cost to quota owners while producing robust outcomes for use in stock assessments.

The Deepwater Group has commissioned over 30 acoustic biomass surveys of orange roughy in New Zealand waters since 1998.

“DWG continues to engage with a variety of scientific institutions towards achieving improved fishery performance with respect to the environment, most recently with particular emphasis on assessing and mitigating the benthic effects of fishing gear,” says chief executive Aaron Irving.

“It is encouraging to see the continuing recovery of a prize species that were severely overfished in the 1980s following its discovery.

“We fish it conservatively to the extent its sustainability is recognised by the Marine Stewardship Council which has applied its gold standard accreditation.”

The San Waitaki catch was frozen at sea in dressed form and further processed into fillets back on shore in New Zealand.

It is bound for the US ready-to-consume market, according to Sanford’s Colin Williams.

The whole fish market in China has declined from previous volumes but demand remains strong in the US.

Echogram image of the Morgue feature. The left screen shows the echogram (i.e. fish finder) image. The solid red area indicates the seafloor, above which a large school of orange roughy was measured. The right image shows a three-dimensional view of the extinct volcano feature. Four AOS transects were made over the Morgue. Multifrequency acoustics were able to classify regions of backscatter. The blue pixels in this image indicate backscatter from the feed layer (400-600 m depth) which consists of small fish, squids, jellies and crustaceans. The orange pixels indicate large non-gas bladder fish (i.e. orange roughy). Regions of orange roughy were observed on all sides of the Morgue. (photo: Tim Ryan)