David Middleton: Drilling down for the cold hard facts on the Ross Sea

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Dr Gareth Morgan describes environmental groups campaigning for a closure of the Ross Sea toothfish fishery as "ideological nutters" and notes that their campaign relies on misconceptions and misinformation.

In the most recent salvo in this debate, Dr David Ainley and Dr Clive Evans provide their opinion as scientists who "have spent numerous seasons conducting research in the Ross Sea". The debate about Ross Sea fishing is clearly an ideological one - but scientists have as much right to an opinion as anyone.

However, for a public seeking to become informed about a debate where the environmental groups are now promoting a US proposal for Marine Protected Areas in the Ross Sea over that of New Zealand, the question is whether Ainley and Evans provide an objective scientific view or simply repeat the misconceptions identified by Morgan.

Ainley and Evans promote a reliance on data from their programme at the US's McMurdo Station - rather than data from the fishery - to monitor the status of the toothfish population. They describe a large decrease in the catch of toothfish in their monitoring programme, and attribute this to the impacts of the fishery.

The reduction in toothfish catch rates at McMurdo in the early 2000s is much greater than the reduction in the population due to fishing determined by the stock assessment carried out by Niwa.

Ainley and Evans speculate that the population distribution must also have contracted northwards. But this is only speculation, not a conclusion from scientific monitoring.

A range of factors other than the fishery could be responsible for changes in catch rates at McMurdo. Some of these include: the gap in the monitoring programme between 2001 and 2007 icebergs blocking McMurdo Sound in 2001-2005, or environmental remediation at McMurdo.

The reality is that there has been no scientific work to reliably assess the reason for the change in catch rates at McMurdo. But, while it is an interesting puzzle, I would question whether the lack of a definitive explanation really matters.

Long-term scientific monitoring programmes are valuable, but they must be appropriate to the questions at hand. Unfortunately, relying on a data series from a small hole drilled through the ice at McMurdo to monitor the entire Ross Sea toothfish population is akin to relying on data collected just off the Leigh Marine Laboratory to monitor fish populations from the whole east coast of the North Island.

Contrast this with the recent New Zealand-led survey which, despite being focused only on young toothfish in the southern Ross Sea, surveyed 59 locations within a 30,000sq km survey area. In a single year the New Zealand survey provided biological data from over 2500 toothfish - more than half the total measured over 40 years at McMurdo.

Of the almost 5000 toothfish tagged at McMurdo only 17 have been recaptured, providing very sparse data on fish growth. Yet tagging in the fishery has yielded around 1000 recaptures, providing a much richer dataset on toothfish growth, movements and abundance.

The New Zealand public might question whether the current promotion of a US marine protected area proposal over that of New Zealand's is based on a similarly narrow worldview.

Would readers of Ainley and Evans' piece have even realised that New Zealand already has a comprehensive marine protected area proposal for the Ross Sea, or would they have been left with the impression that New Zealand was simply rejecting all such proposals?

David Middleton is chief scientist at Seafood New Zealand.

- NZ Herald

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