Climate Shift Pushing Sportfish South

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Taken from Fishing World email newsletter

26 Jul 2012

Article courtesy: Fisheries Research & Development Corporation (FRDC)

MARINE waters in Australia's south-east have been branded a climate change "hotspot", and while global warming will present challenges for the recreational fishing industry, scientists have also forecast better offshore fishing opportunities.

Australia's south-east is expected to lure increasing numbers of rec fishing enthusiasts, with research indicating warming currents will extend the distribution of several species further south.

In March, scientists at the South East Climate Change Recreational Fishing Workshop in Queenscliff, on Victoria's Bellarine Peninsula, predicted the wider range of species would improve offshore fishing opportunities. But they warned that the shift would simultaneously require adequate planning to ensure sustainable management of fish stock levels, particularly for vulnerable recreational species including black bream, King George whiting and snapper.

The forum was convened by the Victorian Department of Primary Industries (DPI), which coordinates the South East Australian Climate Change Program in collaboration with neighbouring states and the Commonwealth. Researchers, fisheries managers and recreational fishing industry leaders discussed the latest climate change and fisheries science specific to Victoria, Tasmania, South Australia and southern New South Wales.

Fisheries Victoria climate change policy manager Dallas D'Silva said the workshop was an important part of FRDC-funded research to examine options for recreational fisher engagement and stakeholder management to address the impacts of climate change on south-eastern fisheries.

"Overfished or depleted stocks will be less resilient and more vulnerable to the effects of climate change, so stakeholders, fisheries management and natural resource management agencies need to work together to develop adaptation strategies under the ethos of 'fish for the future'," D'Silva said.

The FRDC project, Implications of climate change for recreational fishers and the recreational fishing industry, is preparing case studies to inform regional fisher-driven adaptation strategies and to identify carbon-mitigation opportunities for the recreational fishing sector.

As part of the national project, concurrent studies in Western Australia and tropical Queensland are addressing the impacts of climate change on different fish species. A final report will be prepared for recreational fishers in south-eastern Australia and regional nodes in WA and Queensland to clarify potential fish stock changes to 2030 and suggest how these changes can be tackled.

"Adaptation is about taking advantage of opportunities and reducing vulnerability; it's about effectively managing the risks through habitat improvement, environmental flows and adjustments to management controls," D'Silva said.

"Marine waters in Australia's south-east have been identified as a climate change 'hotspot', with observations of increased ocean temperature, salinity, sea levels and currents; decreased pH and rainfall; and more frequent extreme weather events."

The forum heard the East Australian Current (EAC) has strengthened by 20 per cent over the past 50 years and is likely to strengthen by another 20 per cent by 2100, resulting in more warm water subtropical species in parts of Victoria and improved prospects for offshore recreational fishing.

Physical changes

Ocean warming has been observed around the world, with an average global increase of 0.6°C. However, Institute for Marine and Antarctic Studies, University of Tasmania, researcher Gretta Pecl told the forum the rate of warming in south-eastern Australia was 2.3°C higher.

"The greatest warming this century in the Southern Hemisphere is expected in south-east Australian waters and warming on the east coast can largely be attributed to the EAC, which is pushing further south and persisting for longer throughout the year," Pecl said.

The EAC's increased southward extension was linked to intensifying westerly winds south of Australia that "spin up" the South Pacific subtropical gyre. "This is due to a combination of enhanced greenhouse warming (anthropogenic) and ozone depletion," she said. With sea surface temperature also expected to rise, scientists have predicted that by 2070 the EAC will become a permanent, rather than seasonal, feature of the Tasmanian east coast.

On the move

Warming waters in south-eastern Australia will trigger biological responses, including an overall change in pelagic species distribution. Gretta Pecl said the strengthening EAC is also pushing new 'range extension' species including yellowtail kingfish, cobia, mahi mahi, skipjack tuna, wahoo and Spanish mackerel into southern waters.

"This will provide opportunities for the recreational and charter fishing sectors, but it will need to be monitored and managed," she said.

The leader of CSIRO's Marine Climate Impacts and Adaptation Stream, Alistair Hobday, used predictive modelling to indicate the likely future occurrences of 14 species throughout each month of the year. In 95 per cent of the 25 scenarios studied, most species moved south, pointing to a poleward shift.

The scientific evidence is backed by recent sightings of blue marlin and striped marlin off Tasmania and Gippsland, and marlin, cobia, wahoo and Spanish mackerel in southern NSW. Alistair Hobday's modelling suggests that between now and 2100, the endangered southern bluefin tuna and the heavily fished yellowfin tuna will continue to venture south.

Conversely, scientists told the Queenscliff forum that important coastal and estuarine fish species valued by recreational anglers, such as black bream, King George whiting and snapper, are susceptible to population decreases as a result of a changing climate.

Vulnerable species

The manager of the Victorian DPI's Fisheries Research Branch fish ecology program, Greg Jenkins, told the forum that interdependencies between King George whiting populations in South Australia and Victoria would need to be clarified to ensure successful adaptation to climate change.

"We know whiting don't reproduce in Victoria – the hypothesis is that larvae reaching the Victorian fishery may be coming from South Australia," Greg Jenkins said.

"But as the resource base in each state may alter under climate change and be affected by resource use in the other states, cross-jurisdictional management is likely to obtain the best outcome for this species."

In the case of black bream he said the salt wedge formed in estuaries when less dense freshwater flows over the top of salty ocean water created the interface where black bream larvae and eggs were prevalent. However, he said drought conditions during the past decade were similar to those predicted under climate change, with "lower than normal freshwater flows" forcing the species further upstream in search of lower salinities for favourable spawning conditions.

"This will contribute to a population decline in areas such as the Gippsland Lakes – Victoria's most important recreational bream fishery," he said.

"Contraction in range is also possible with increasing temperatures and spawning may occur earlier."

Fisheries Victoria research scientist Paul Hamer said freshwater flows that influenced plankton production prior to the snapper spawning season would also be impacted by climate change, potentially affecting larval food supplies and recruitment success. He told workshop participants that models were under development to study climate change implications for the snapper fishery. He anticipated greater larval dispersal further south, more recruitment in Tasmanian waters (possibly at the expense of NSW) and highly variable stock populations in western Victoria and South Australia.

Adaptation principles

The workshop concluded that management strategies must ensure fishing does not exacerbate the impact of climate change on fish stocks.

Industry experts recommended that recreational fishers:

• become 'citizen scientists' by reporting unusual catches and sightings to fishery managers – for example, the Redmap web- based interactive facility to be launched nationally in October 2012 (www.redmap.org.au);

• participate in angler diary programs to inform cost-effective and participative monitoring – for example, the Victorian Angler Diary Program (www.dpi.vic.gov. au/fisheries/science-and-research/angler-diary-program);

• develop future opinion leaders to help communicate climate change and recreational fishing information to the sector;

• and lead recreational sector climate change mitigation measures.

Industry experts recommended that fishery managers:

• ensure legislation and policy is flexible, adaptive and capable of responding to emerging issues;

• collect information on key species using cost-effective monitoring programs that allow early detection of climate change impacts on fish populations;

• review recreational catch limits and other management controls to ensure sustainable fisheries management;

• disseminate information and engage the recreational fishing community through forums, workshops and seminars;

• work with relevant land, habitat and water managers to ensure fisher and fishery needs are understood and accommodated;

• and assist relevant land managers to improve fisher access in areas currently restricted due to limited infrastructure.