Australia's long-term commercial fish catch is estimated to be millions of tonnes more than what has been officially reported, analysis has found.

A catch of more than 8 million tonnes has been reported for 1950-2010 to the United Nations Food and Agriculture Organisation.

However, researchers from the University of British Columbia's Fisheries Centre estimate that an extra 4 million tonnes of fish was caught in that period, although it was deemed to be "discards".

Discarding is the process of returning unwanted catches to the sea, dead or alive, either because they were too small, above the quota, or the wrong type.

UBC Professor Daniel Pauly said, without counting them, we are not getting a true picture of the state of our fisheries.

"Some of the underreporting is innocent," Professor Pauly said.

Estimates of the footprint of fisheries in Australian and New Zealand oceans in the 1950s compared to in the 2000s. ( Supplied: Professor Daniel Pauly )

"For example this count — fish that are discarded are not reported by any country — but it ought to be counted because in the long term or maybe in the medium term, discarding is going to be abolished.

"We cannot afford to throw away so much food."

Researchers used statistics from five large trawl fisheries, combined with research on rates of by-catch to calculate discards.

Australia's level of discards has declined by 90 per cent since the peak in 1990 because of new technologies being used by trawlers.

The European Union has legislated to ban the practice and Professor Pauly expects that the rest of the world will eventually follow suit.

The South East Trawl Fishing Industry Association chief executive Simon Boag said the focus should be on the future management of our fisheries — not the past.

"What we've done in Australia is we've been able to get our non-commercial catch of fish down and down, so our discard total has come down a lot," he said.

"And that should be the focus — on where we're currently at and how to continue to make it better.

"What we do here is add the fish that's landed [caught] to the fish that's been discarded and we make sure that number is sustainable."

Australia 'world leader' in fishing management

Late last year, the Australian Bureau of Agricultural and Resource Economics and Sciences released its fishery status report showing that no Commonwealth-managed fisheries were subject to overfishing.

Professor Pauly said Australia stood as a world leader in its fisheries management — but warned the nation was at a crossroads.

"There is a crisis in fisheries globally — we fish too much, the stocks are going down, and this is gloom and doom," he said.

"But Australia is different in that it has not let big boats, big foreign boats exploit the so-called surplus."

The Federal Government has banned super trawlers — boats larger than 130 metres.

However, a 95-metre factory freezer ship recently killed eight dolphins and four seals in just its first two voyages in Australian waters.

It forced the Australian Fisheries Management Authority to ban mid-water trawlers from fishing at night.

"Once they are there they want to access more of the resources and the resources are in better shape in Australia than elsewhere and therefore there are more resources to be had," Professor Pauly said.

"On short notice they could make huge catches and 10 years later you wouldn't have any, and you would be in the same mess that all of the other countries are in."

But the South East Trawl Fishing Industry Association does not believe Australia will be a target.

"I think it's unlikely given the relatively low productivity of Australian fisheries but in any event what's important is how much fish you catch, not how you catch it," Mr Boag said.

Government review of marine reserves underway

The Government is also undertaking a review of Commonwealth Marine Reserves.

How, or if, any changes will impact fisheries will be a decision for the Federal Government.

The latest update from the co-chairs published recently said that consultations had been completed and that it was now awaiting advice from its expert scientific panel.

"The review received over 13,100 written submissions and 1,859 responses to the online survey," the co-chairs said.

"We have referred a number of the issues that have been raised with us to the Expert Scientific Panel for assessment and feedback.

"Some of these are national in scope but several relate to specific issues surrounding individual areas or regions."

The process is likely to take four to six weeks, with a draft for the government expected to be completed in the next few months.