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Are Deepwater Fisheries Overfished, or Simply Misunderstood?

21 May 2012

Speaking at the World Fisheries Congress 2012, Graham Patchell, from the Sealord Group New Zealand and Chief Scientist for the Southern Indian Ocean Deepsea Fishers Association (SIODFA), asked whether deepwater fisheries were overfished or simply misunderstood. Charlotte Johnston, TheFishSite editor reports.

Mr Patchell said that the biggest challenge for deepwater fisheries was ensuring that data, that can really tell you what is happening in the deep ocean, is available for management decision making.

He went on to say that there was a lot of premeditated information about deepwater fisheries that was inaccurate. In fact, he said, many "overfished" stocks are now seen as sustainably managed, as the industry's understanding of the stocks has increased.

Examples of poorly understood fisheries

New Zealand Challenger Orange roughy

In 2000 a catch per unit effort analysis modelled the apparent decline of the New Zealand Challenger orange roughy stock to three per cent of virgin biomass.

ICES used this study to support their view, in recommendations to NAFO and NEAFC, that deepwater fisheries cannot be sustainably managed.

However further studies and industry findings showed stocks moving back to the area, nine years after the fishery was closed. What had actually happened, explained Mr Patchell, was that fish stocks had moved out of the area (not that numbers had dropped due to overfishing).

Because of this the fishery reopened in 2010.

To data, 2012 data has shown that orange roughy compensate to fishing, like other fish species, with new recruitment occurring, and fish maturing earlier. Mr Patchell said that orange roughy usually mature at 24 years of age, but maturing at 12-13 years of age was becoming more common.

He said there was still 20,000 tonnes or more of "unverified" orange roughy to be added to the data, which would put the stock at greater than 40 per cent biomass.

Over the next two months, two vessels are working in the area to get new estimates.

New Zealand Northeast Chatham Rise Orange Roughy


In 2011, data showed the world's largest orange roughy stock declining. The data showed that in 2002 there were around 65,000 tonnes of orange roughy, but by 2011 the number of stock had fallen to just less than 20,000 tonnes.

The conclusion at the time was that there must be recruitment failure, with the best scientific advice at the time being to cut the quota. Mr Patchell asked though whether something else could be happening that is causing a decline in fish numbers in the area.

As it turned out, the orange roughy stock had only moved 20 miles away from where the survey had been going on for 10 years. Instead of stocks decreasing, as was previously thought, 30-40,000 tonnes of fish had been missed out of the surveys, and it turned out that stocks were increasing.

Ensuring Sustainable Fisheries

A key message of the Southern Indian Ocean Deepsea Fishers Association (SIODFA) is that the seafood industry must be proactive to ensure sustainable fisheries.

In response to this, Mr Patchell explained that prior to carrying out any fishing 15 years ago, the Sealord Group mapped out the entire habitat, over 160,000 kmĀ².

Studies carried out by SIODFA have considered the impacts of bottom trawl fishing and Benthic Protected Areas (BPAs) have been established to maintain and protect biodiversity.

This has been recognised as a major contributor to the Ecosystem Approach to Fisheries (EAF). The "Coral" BPA area has also been recognised by the International Union for Conservation of Nature (IUCN) as having one of the largest deepwater coral reefs ever discovered.

Other efforts by industry, Mr Patchell described, include fitting high resolution video cameras fitted to bottom trawl nets, to ensure there was no significant impacts on vulnerable marine ecosystems.

One of the main issues that has been raised is, how do you get quality scientific data for 30-40 widely separated stocks, that cover an area of over 1000 miles.

Mr Patchell said this can only be done through industry assessments, using commercial vessel acoustics and splash surveys.

He pointed out that it wasn't just fished stocks that move, but that stocks that have never been fished before also move about. A five year acoustic time series of two stocks which were tracked showed them moving up to 15 miles a day, prior to ever being fished.

Concluding, Mr Patchell said that in 2013, Sealord will deploy into the Indian Ocean, the first real time multi-frequency acoustic system with cable link, being built by Australia's CSIRO.

Despite many years of significant research and many years of commercial fishing, the true status of many deepwater stocks is poorly understood.

"Deepwater fisheries can, and are being, sustainably fished, and it is time to erase the outdated assertions of these being unsustainable fisheries.

"The use of commercial vessels and collaboration between industry and marine scientists has led to an increase in data available."

May 2012

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