(AU) Empty Nets And Tropical Fish In Tasmania As Climate Change Hits Southern Ocean

Sydney Morning Herald - Royce Millar | Chris Vedelago

Rising temperatures and climate change have been blamed for the failure of stocks of some of the most popular eating fish in Australia’s Southern Ocean to recover from declines despite more than a decade of protection.
The troubling findings come as new modelling from the CSIRO shows further temperature rises already “locked in by past emissions” could see fish stocks fall by another 20 per cent within the next two decades.

Sea surface temperatures off the coast of Tasmania
November 23, 2010 -2017

Source:  IMOS (Integrated Marine Observing System)

Dr Alistair Hobday, a principal research scientist at the CSIRO, said there was “no doubt” climatechange was an important factor in the failure of some over-fished species to recover.A report by the government’s Fisheries Research and Development Corporation has found ocean temperatures increased by nearly 2 degrees over the past 80 years in the Southern and Eastern Scalefish and Shark Fishery, a “global hotspot” that was warming at almost four times the global average.
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.


What role does climate change play in the changing composition of fish in Victoria's waters? Andy McLaughlin of McLaughlin Consolidated Fisherman believes there are other, more immediate, threats to the industry.

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.

In danger

Orange Roughy	Southern Rock Lobster
Abalone	Gummy Shark
Marlin	Blue Grenadier

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.”

Illustration: Matt Golding

In contrast, Dr Hobday said the fishing industry is increasingly of the view that climate change was exerting a noticeable influence: “Like smart farmers fishermen recognise the inescapable changes happening around them.”
The latest modelling from the CSIRO says climate change will be responsible for a damaging 1 degree rise in average water temperatures by 2040 and likely increase the intensity of extreme events.
“The majority of models also indicate that many of the [species in the SESSF] may decline in abundance by 20 per cent or more as a result of climate-related changes,” the soon-to-be-released report says.
Among those to be rated at a high risk of being affected are orange roughy, oreos, blue grenadier, southern rock lobster, abalone, marlin, and several species of shark, with some species anticipated to see drops in stock numbers of up to 50 per cent.

Links

• Climate Change Threatens The World’s Fisheries, Food Billions Of People Rely On
• Suffering In The Heat: The Rise In Marine Heatwaves Is Harming Ocean Species
• Heatwaves Sweeping Oceans ‘Like Wildfires’, Scientists Reveal
• Australia's Marine Heatwaves Provide A Glimpse Of The New Ecological Order
• Marine heatwaves threaten global biodiversity and the provision of ecosystem services
• Marine heatwaves are getting hotter, lasting longer and doing more damage
• Coastal seas around New Zealand are heading into a marine heatwave, again
• Why we need to start categorising marine heatwaves like hurricanes
• Climate-driven regime shift of a temperate marine ecosystem
• Conservation implications of ecological responses to extreme weather and climate events
• Surviving Great Barrier Reef corals have higher heatwave resistance