New Year survey marks 20th anniversary of Chatham Rise fish surveys
On New Year's Day, NIWA's research vessel Tangaroa departs for its first voyage, since its recent $20 million dollar upgrade, making its twentieth consecutive trip to the Chatham Rise to study the abundance of important fish species.
The Ministry of Fisheries funded survey has been undertaken by NIWA scientists onboard Tangaroa every year since 1992. The main aim of the survey is to estimate the abundance of hoki and other commercially important species (such as hake and ling), but during the 20 consecutive surveys NIWA scientists have also been able to study other aspects of deepwater biodiversity on the Chatham Rise, including fish distribution, abundance, and ecology.
The surveys are conducted by trawling at depths of 200–800 metres. Trawling locations are randomly selected using a specialised computer programme. The trawl is towed for 3 nautical miles (5.5 km) at a speed of 3.5 knots (6.5 km/h) at each location.
Since the surveys began, scientists have recorded a total of 558 species or species groups and analysed more than one million individual fish, squid, crustaceans, and benthic fauna to help establish biomass trends and spatial and depth distributions. They enter a catch record of all species into a trawl database and bring any species unidentified at sea back to NIWA for identification.
The surveys have also provided the Ministry of Fisheries with a lot of important information about hoki stocks. Hoki is New Zealand's largest fishery, with a current total allowable catch (TAC) of about 120,000 tonnes. In 2009–10 the commercial catch of hoki from the Chatham Rise was 39,000 tonnes.
Over the last 20 years the proportion of hoki in the trawl survey catch declined from nearly 60 percent in 1993 to 21 percent in 2004, but has increased again to make up 30-40 percent of the total biomass in the past six years.
The other two target species (hake and ling) typically make up 3-4%, and less than 2%, respectively, of the total survey biomass.
NIWA fisheries principal scientist Dr Richard O'Driscoll says the surveys are very important for New Zealand fisheries.
"For most of the species we analyse, the trawl survey is the only fisheries-independent estimate of abundance on the Chatham Rise. The Chatham Rise is also the major nursery area for New Zealand hoki. Juvenile hoki from both eastern and western hoki stocks mix on the Chatham Rise, so this survey provides an opportunity to get an idea of how many small hoki are out there, before they recruit to their respective areas and are caught by the commercial fishery. This allows the Ministry of Fisheries to set an appropriate catch limit which is responsive to the abundance of small fish coming into the fishery.
"The survey provides essential input into the stock assessment for hoki, but also fulfils an important ecosystem monitoring role by providing additional information to improve our knowledge of species distribution and biodiversity," says Dr O'Driscoll.
"During our last survey we trawled deeper than usual, to depths of almost 1300 metres, catching rare and unusual deepwater species, including a giant squid (Architeuthis spp.). Since 2001, we have also been collecting acoustic data to monitor small midwater fish, which are the major prey of hoki."
Ministry of Fisheries Chief Scientist Dr Pamela Mace says the trawl survey is the most comprehensive and consistent time series of species abundance in depths of 200–800 metres in New Zealand's Exclusive Economic Zone (EEZ).
"It provides reliable, statistically valid information on the abundance and size of hoki and other important fish species and is one of the most valuable time series of information we have to enable us to assess and manage these species. Additionally, there is a wealth of information about other species that live on the Chatham Rise. The longer the time series of consistent data, the greater the insights that can be gained about the dynamics of our marine species," Dr Mace says.
NIWA gifts rare and new-to-science fish to Te Papa where they are preserved and stored in the National Fish Collection.
RV Tangaroa departs from Wellington for the 2011 Chatham Rise survey on 1 January.
About the Chatham Rise
- The Chatham Rise is an area of ocean floor to the east of New Zealand.
- It stretches around 1,000 kilometres from near the South Island in the west, to the Chatham Islands in the east.
- The current known as the subtropical convergence occurs over the Chatham Rise, creating a very productive fishing ground supporting some of New Zealand's major commercial fisheries, including hoki, hake, ling, orange roughy, and oreo.
More information about the trawl surveys
- With 20 surveys, the Chatham Rise series is the longest consistent survey in New Zealand.
- The number of individual species or groups recorded has more than doubled since the start of the surveys (from 137 in 1992 to 286 in 2010), mainly due to improvements in the identification of benthic invertebrates. There has been a ninefold increase in the number of invertebrate groups identified over the series of surveys (from 14 in 1992 to 125 in 2010).
- There were 161 fish species or groups identified in 2010, but this was inflated by the capture of deepwater species from extra tows down to 1300 metres.
- The number of fish measured has varied between 30,000 and 80,000 individuals per survey.
- In general, a random sample of up to 200 individuals of each commercial species and some common non-commercial species is measured from every successful tow. More detailed biological data is also collected on a subset of species – including fish weight, sex, and maturity stage.