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King George Whiting Stock Assessment
  |  First Published: July 2006



In commercial fishing terms, the King George whiting is Victoria’s most valuable scalefish. In 2004/05, the landed value of the 138 tonne catch was $1.8 million.

In recreational fishing terms, along with snapper and bream, whiting is the major saltwater scalefish targeted by anglers.

Over the years, environmental and fisheries research has unravelled some of the mysteries of whiting biology and the reasons for seasonal and longer term changes in their availability to fishing.

Publicity, through various media, has improved anglers’ understanding of these factors, helping to diminish conflict with commercial fishers. Reduced commercial fishing effort – through angler-funded buy-outs – along with improved gear and methods, now incorporated in industry codes of practice, have further helped to reduce conflict.

Stock Assessment Workshop

During June this year, Primary Industry Victoria researchers held a stock assessment workshop at their marine fisheries laboratories at Queenscliff. Participants included research anglers, commercial fishers, VRFish and Seafood Industry Victoria representatives, DPI fisheries managers and regional Fisheries Officers.

The researchers summarised the findings of previous assessments and outlined the most recent research findings and fishery trends from commercial and recreational fisheries data.

Throughout the workshop, fishers engaged in the discussion, questioning the researchers and presenting their own observations and views on the state of the whiting stocks and the fishery.

Whiting Biology

During spring at ages of around 105-110 days, 20mm post-larval whiting arrive in Port Phillip Bay and settle among seagrass beds and other suitable habitats.

Post-larvae arrive in Western Port and Corner Inlet at around 115 and 125 days, respectively.

These observations suggest that spawning occurs mainly during June and July, and that the whiting larvae have travelled from west to east.

Modelling of currents suggests spawning sites beyond Cape Otway, possibly as far west as the Coorong, SA.

Captures of 40-day old 9mm larvae off Portland in 1998 suggests a spawning site further to the west. A close relationship has been reported previously between periods of strong westerly winds during winter and strong post-larval settlement and – allowing a lag of three years or so – commercial catches in the bays.

Between 1940 and 2005, five peaks in the annual commercial catches from Port Phillip Bay and Corner Inlet show this relationship.

Recent findings show that larval growth and survival are linked to slightly elevated temperatures in coastal waters.

In winters when the Leeuwin Current – from the Indian Ocean – extends to Victoria, water temperatures rise by around one degree. Indications are that water temperatures off Portland may be a good predictor of whiting larval growth, survival and transport into Victoria’s bays and of catches four years later.

However, other factors including seagrass coverage and juvenile whiting movements also affect how post-larval settlement translates into catches.

Other Factors

In Port Phillip Bay, researchers find most whiting post-larvae off Blairgowrie and Rosebud where the seagrass cover increased over several decades until about 2000.

That increase was paralleled by the increasing trend in annual commercial catches from the Bay.

Fluctuations in the distribution and abundance of seagrass have been a characteristic of the Bay and may occur as a result of natural as well as human causes.

The effect of the recent seagrass decline in the southeastern part of the Bay – and in areas of the Geelong Arm, Corio Bay and Corner Inlet – are not yet known, but the major decline of the whiting fishery in Western Port has been clearly linked with the loss of seagrass in the 1970s.

Post-larval settlement during 2003 and 2004 was very poor, resulting in the recent relatively poor fishing, which is likely to continue into 2007. Settlement in 2005 was the strongest yet recorded, suggesting that we can expect a major upturn in the fishery from 2008.

While the links between post-larval settlement and catches are clear for Port Phillip Bay and Western Port, the picture in Corner Inlet is not so clear.

Despite repeated sampling, very few post-larvae have been found there although the Inlet accounts for over 40% of Victoria’s commercial catch.

It seems that most of the whiting enter Corner Inlet as juveniles after settling either in Bass Strait coastal waters or in the bays.

Some light may be shed on this by a promising line of research based on micro-chemical analyses of the otoliths (ear bones) of whiting from Corner Inlet.

If those fish have previously spent time in Port Phillip Bay, analyses should show a chemical ‘signature’ characteristic of the Bay (also found in snapper from the Bay).

The Victorian bay, inlet and coastal whiting fisheries are based entirely on immature fish – mainly on 2-4 year olds with some 1+ and six year olds.

SA studies show that whiting there become mature at around eight years and 50-60 cm in length, and may live to 20 years.

The rare sightings of mature whiting in Victorian waters hint of the possibility of a separate spawning stock and site in the deeper waters of Bass Strait.

Fishery Indications

Recreational fishers at the workshop reported increased fishing effort and boat numbers in the bays but spasmodic and generally poor whiting catches in the 2005/06 season.

This has been partly compensated by alternatives such as snapper, elephant fish, calamari and the rising popularity of targeting pinkies with soft plastics.

Western Port anglers reported low catch rates of whiting, mainly of larger sizes.

Port Phillip Bay anglers reported poor catches, with interference by undersized snapper a problem.

Records of diary anglers showed catch rates of retained whiting in the bays were barely above 0.5 per hour during the recent season.

Most Port Phillip Bay whiting were 30-42cm with very few undersized caught compared to previous years.

Most Western Port whiting caught were slightly larger with many between 40 and 45cm.

Commercial Reports

Commercial anglers reported generally poor to average catches, mainly of larger whiting, with little sign of the undersized fish that would be recruited to the fishery next year. They observed the widespread loss of seagrass in the Bay. The uniform adoption of conservative mesh sizes in haul seine nets was said to have effectively eliminated meshing of undersized whiting.

Anglers and commercial fishermen from all areas commented on the problems caused by the autumn growth of fine brown algae, which blankets the bottom in shallow water, covering baits and clogging nets.

Commercial fisheries statistics showed that the haul seine fishery – now over 180 years old in Victoria – continues to be productive, with annual catches in Port Phillip Bay and Corner Inlet reflecting whiting abundance.

In contrast, annual haul seine catches from Western Port and annual mesh net catches from the bays and inlets have declined to record low levels as a result of reduced fishing effort.

Much of the effort decline coincides with the removal of effort by the first voluntary buy-out of commercial bay and inlet licences in 2000.

Increasing numbers of seals is also a factor in reduced mesh netting activity.

The State of the Whiting Stock

The variations in annual whiting catches and catch rates continue to fall within the range observed over many years and can be explained in terms of variations in annual settlement of post-larval whiting.

In turn, these variations can be explained and – increasingly – predicted in terms of environmental conditions.

On present indications Victoria’s whiting stock is in a healthy condition, with sufficient numbers of juvenile whiting avoiding fishing pressure to mature and reproduce in coastal waters beyond the reach of the fishery.

The fishery prospects from 2008 look very promising.

While many uncertainties remain about the distribution and life history of whiting, there are no worrying signs in terms of fishery impacts.

Whether the recent declines in seagrass are the result of human activities is unclear, but ongoing monitoring will be needed particularly if the channel deepening work in Port Phillip Bay proceeds.

In terms of the larger scale environmental factors determining successful annual post-larval settlement, climate change looms as a potentially significant factor.

Priorities

The workshop identified continued monitoring of post-larval settlement in Port Phillip Bay (as a predictor of catches 2-3 years later) and monitoring of fishing catch, effort, size and age composition as the highest priorities.

Additional research needs to include studies of the links between SA spawning populations and Victorian stocks, whiting movements between Victorian bays and inlets, and studies of habitat use by undersized whiting, including the relative importance of seagrass and sand habitats.

A current SA study is addressing the question of survival rates of hooked whiting released by anglers.

Anglers who catch whiting with ripe gonads are asked to report them to PIRVic’s Queenscliff research centre (03) 5258 0111 and to retain either the whole fish or the frames and gonads for collection by researchers.

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