More accurate information on Orange Roughy
24 July 2007
Scientists are using advanced technology to survey orange roughy on the Chatham Rise - and early results reveal better information for determining the fishery’s stock size than ever before.
Commissioned by the Ministry of Fisheries, NIWA scientists are using a device built by scientists at Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) that combines a fishing trawl net with a high-resolution video camera and acoustic equipment.
As the vessel moves along, scientists record acoustic echoes alongside images of orange roughy and other fish. This allows the ‘target strength’ for orange roughy to be determined, which in turn helps measure the amount of orange roughy present.
Until now, identifying orange roughy has been difficult – largely because orange roughy have an oil-filled swim bladder that produces a much weaker acoustic signal than the typical air-filled swim bladders of most fish. So when signals come in, it’s not clear whether they are from orange roughy or another kind of fish.
This new technology helps solve the identification problem and complements other acoustic research that New Zealand’s Deep Water Fishing Group is undertaking in collaboration with NIWA and CSIRO.
Ian Doonan, on board NIWA’s research vessel, the Tangaroa, says this is the first time simultaneous images and acoustic echoes have been collected in a large group of spawning orange roughy - and the footage is impressive.
“We’re able to identify orange roughy so clearly that we can see them diving in reaction to the net.
“The results will improve estimates of acoustic orange roughy biomass for both New Zealand and Australian waters. Essentially, that means more reliable information on the amount of orange roughy in the area.
“It will also help feed into more accurate assessments of stock numbers across the board.”
Ministry of Fisheries deepwater fisheries manager, Stefan Leslie, says this type of research has a key role to play in terms of helping make more informed decisions about the management of orange roughy.
“It’s a fishery that has been important for decades – providing jobs and export earnings for New Zealand along the way. To ensure this can continue, we need better information and this type of research is helping us achieve that.”
Ministry of Fisheries chief scientist, Pamela Mace, says the work is also a reflection of a large co-operative effort between government, trans-Tasman science organisations and the fishing industry’s Deepwater Group – all working together to develop an efficient and informative research programme.
** A swim bladder is also known as a ‘gas’ bladder. It is used to keep the fish buoyant. The bladder has a gas gland that can introduce gases (usually oxygen) to the bladder to increase its volume and thus increase buoyancy. To reduce buoyancy, gases are released from the bladder into the blood stream and then expelled into the water via the gills. Below 1,000 metres or so the pressure is too great and an air-filled swim bladder is unable to function – gas cannot be produced. Most fish at these depths lack swim bladders or, like orange roughy, have bladders that are filled with oil, which gives a certain amount of buoyancy control, but is not as effective as a gas-filled swim bladder.
** Target strength refers to the strength of the return echo from individual fish.
About the survey work
The trawl area is 5100 km2 covering depths of 824 to 1250 m, and consists of a strip 15 km wide (on average) and 350 km long. The area is north and east of Chatham Island, and is 8 hr steam from the Island at the closest point.
- This survey will form part of an assessment of the orange roughy stock on the north-east Chatham Rise which in turn helps set quota limits.
- This is the second combined wide area trawl and acoustic survey of the Northeast and eastern Chatham Rise. The 1st was in 2004.
- In addition to the target strength experiments, the 2007 Tangaroa voyage will also deploy fixed cameras on the seabed in an attempt to record fish behavior in its natural environment.
- The at-sea survey work is on-track for completion at the end of this month.