The affected region sweeps from the lower east coast of Western Australia across Victoria and Tasmania to the Queensland-NSW border - one of the most productive ocean zones in the country. Stringent new controls were introduced in 2005 to try and reverse the effects of long-term over-fishing in the area but new data shows that by 2015-16, commercial fishing operators were still catching less than half their allowed quota for more than two-thirds of species. “When you reduce pressure [from fishing] you expect the stocks to improve. If you are catching fish and then you stop catching fish, the numbers of fish should come back. But they haven’t, and climate change is stopping that recovery in some cases, such as for jackass morwong, eastern gemfish, and blue warehou,” Dr Hobday said. “Historically over-fished species (eastern gemfish, school shark, blue warehou and most recently redfish) have shown little sign of recovery despite over a decade of the lowest catches on record resulting from significant management changes under ... rebuilding strategies,” the research report found.

Tropical fish and other species from northern waters are now being seen in the southern ocean along with more than 100 other marine species which have been migrating. Pink snapper for example, are increasingly common in Tasmania waters, while traditional cool water fish are being pushed further south. Species of sea urchin and octopus better known in NSW and Victorian waters are now prevalent and problematic in Tasmania. Loading Replay Replay video Play video Play video Of the major species sought by fishers, only flathead, gummy shark, pink ling and school whiting were returning catches of about 80 per cent of the quota. Climate change not only increases water temperatures but also boosts acidity, reduces nutrients, and changes water currents. Oxygen levels also decline in warm water, which means the ocean can support fewer fish. The interaction of these factors forces shifts in the feeding, breeding and travel patterns of some fish species. The FRDC report, which was produced in cooperation with fishing industry representatives, suggests that other factors that could be affecting catch rates include reduced fishing grounds from the growth of marine parks, the declining number of boats in the fleet, and increasing operational costs limiting the ability to fish.

Study participant Simon Boag, executive officer of South East Trawl Fishing Industry Association, Southern Shark Industry Alliance & Small Pelagic Fishing Industry, said that while the industry accepted the science of climate change, many working on the water had not yet seen the practical effects. Fish in danger “What they see is huge variations either way - strong currents, weak currents. We have seen the emergence of stocks of fish that have never really featured before and then they go away again." “I think this is one of the reasons that we haven't really come up with a strategy as an industry to deal with climate change - we don't really know if things are going to get better or worse. The costs of [fish regulation] are much more extreme and much short term and real, than the long term slow and steady effects of climate change.”