Revealing toothfish secrets

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NIWA fisheries scientist Steve Parker says the 1.55 million square kilometre Ross Sea Marine Protected Area (MPA) in the Southern Ocean will help further research into the ecology of Antarctic toothfish.

Stu Hanchet wrangles an Antarctic toothfish at the surface for tagging. [Photo: Laura Ghigliotti]

Toothfish are found throughout the Ross Sea, and may be important prey items for top predators such as Weddell seals and killer whales.

Steve has been travelling to the sea ice of McMurdo Sound since 2014 to develop survey methods to understand the ecological role of toothfish and their interactions with top predators in the area.

More toothfish

The sixth annual Ross Sea Shelf Survey of sub-adult Antarctic toothfish was completed in January 2017. The results showed a new relatively strong year class moving onto the shelf region, to be used to index year class strength in the stock assessment.

“The MPA creates the framework and scientific rationale for understanding how this polar marine ecosystem functions and, by doing that, understanding how to best conserve it.”

Parker is rising to the challenge of working in the extreme Antarctic environment, cutting through 2 metres of sea ice to then study a species that lives in the dark more than 500m below the surface in water near minus 2°C.

“We have already shown that the fish living under the ice in coastal regions are large, slow growing, old fish, and that they likely live there to eat the abundant Antarctic silverfish, but do so at the peril of being eaten by seals and killer whales.

“We are now trying to understand if Weddell seals and killer whales eat toothfish occasionally, or if they rely on them during certain times of the year when the melting sea ice gives them access to these areas.”

The work will require a NIWA team to spend several seasons on the sea ice to develop ecosystem indicators and a monitoring plan to detect any changes due to climate change or the effects of fishing in areas outside the MPA.

Counting corals

A master’s student from the Universite de Brest, France (Anne Boulet) is working with NIWA in Nelson on a six-month internship to analyse benthic invertebrate data from the Ross Sea.

Habitat-forming benthic invertebrates are caught in the process of catching toothfish in the Ross Sea. The project examines more than 8,000 observations of benthic organisms such as corals, sponges, or anemones to create distribution maps. These will be used to plan studies into the effects of fishing on the Ross Sea benthic ecosystem as part of the new Ross Sea Marine Protected Area.

[This feature appeared in Water & Atmosphere 19]

Research subject: AntarcticaFish