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Rebuilding Port Phillip Bay shellfish reefs
  |  First Published: August 2014



Shellfish reefs are the temperate zone's equivalent to tropical coral reefs: they provide the foundation and the living structure on which healthy bottom communities and fish populations depend.

Around the world shellfish reefs - particularly oysters - have disappeared from many major embayments, resulting in reduced fisheries productivity, biodiversity and water quality. At the time of first European settlement, much of the floor of Port Phillip Bay was covered in shellfish-based life that owed much of its diversity and productivity to a solid foundation of native flat oysters. In less than a century the oyster beds were wiped out by over-harvesting and the post-1963 scallop and mussel dredge fisheries completed the break-up of the shellfish-based ecosystems on a Bay-wide scale. Despite this, the Bay continues to function as what we generally regard as a healthy and productive system. Well, that could be about to change - all for the good. Victoria has all of the necessary ingredients for re-establishing broad areas of natural and self-sustaining beds of oysters and mussels and all the associated marine life. Enterprising members of the Albert Park Yachting and Angling Club (APYAC) have teamed up with researchers from Fisheries Victoria and Melbourne University to develop a staged approach designed to bring this about.

HISTORICAL PERSPECTIVE

While we don't know much about the 19th century Bay ecosystem and fisheries we do know that, like Western Port Bay and some smaller inlets, it supported thriving industries based on harvesting the abundant native flat oysters. In fact, Victoria's first fisheries legislation was the 1859 Act for the regulation of the Oyster Fisheries in Victoria. From the early 1840s, oysters were shipped to Melbourne from as far away as Port Albert in Corner Inlet. As in the London of Charles Dickens' times, oysters and beer were popular fare of the working people in Melbourne's early days. Oysters were cultivated, raked and hand-gathered in the shallows and dredged up by steam-powered vessels from deeper waters. They weren't just harvested as seafood - oyster shells were burnt in lime kilns that provided essential supplies for stone and brick buildings as Melbourne, Geelong and outlying centres took shape. Current designations such as Limeburners Point and Limeburners Bay at Geelong reflect those times. Whether as a result of harvesting alone or through the added influences of industrial and domestic contamination plus land clearing in the catchments, by the 1920s the oyster stocks were extinguished as renewable resources. Today, thick layers of old shells covered by several centimetres of sediment extend from Williamstown, down the western shoreline towards Point Wilson, in Corio Bay and off the eastern beaches from Mentone to Seaford.

By the time the scallop fishery started in 1963, mussel beds were the predominant more-or-less permanent fixtures across large areas of the Bay floor. Attached to old oyster shells and rubble-reefs, they provided the base for a wide range of bottom dwelling animal and plant life. Being so widespread and easily located they acted as a focal point for commercial and recreational fishers who targeted the snapper schools that held there predictably, feeding on mussels and associated life.

Until the fishery was closed in 1996, scallop dredging over much of the Bay repeatedly raked over the beds of mussels, ascidians (‘spuds’ or sea squirts) and associated life to the point where they ceased to function as stable productive ecosystems. In the 1970s, during a downturn in the scallop fishery some boats from Mordialloc and Williamstown switched to dredging mussels. By the time the Government put a stop to it in 1987, this fishery was harvesting up to 1500 tonnes of mussels annually, mainly from the Altona-Pt Cook area and on the reefs that run parallel to the shore from Parkdale to Seaford. Long before then, anglers and commercial fishermen had lamented the loss of mussel beds which functioned as "holding grounds" where feeding snapper could be located readily and on a predictable basis for extended periods during spring.

WHAT'S HAPPENED SINCE SHELLFISH DREDGING STOPPED?

Intuitively, the termination of commercial shellfish dredging could be expected to lead to revivals of the former massive mussel, oyster and scallop beds in the Bay. But no - while these "resources" were being fished down, the changed Bay environment was being colonised by thousands of tonnes of exotic species. Among them were bottom filter-feeders which have out-competed oysters and mussels, plus new forms of shellfish predator including the Northern Pacific sea star. Even without those influences, the removal and burial of extensive beds of shell material that provide settlement habitat for your shellfish put an end to any chance of significant natural reef recovery.

As a result, today the main concentrations of scallops are found in the southern part of the Bay while recovery of mussel beds has been localised and short-lived and oysters are patchily distributed in small clumps. Since the early 1980s, commercial mid-water farming of mussels on suspended ropes and trials with flat oysters (and scallops) have shown that the Bay continues to be capable of supporting these shellfish. The more obvious obstacles to mussels and oysters forming natural shellfish reefs again are:

•the lack of suitable substrate to attach to and grow on

•native and introduced predators

•introduced competitors.

What's also happened in the years since shellfish dredging ceased is the recovery of the Bay snapper fishery to levels that even many older fishers rank as "the best in living memory". However, anyone who fished for snapper on the pre-1970 mussel reefs would agree that this fishery could be even better if broad-scale native shellfish reefs are re-established along with the associated life that snapper feed on.

So, now we have a highly modified Bay with, effectively, none of the former widespread native shellfish reefs that were the foundation of healthy bottom communities. That's a bit like the Great Barrier Reef without the living coral structures that are the foundation of tropical reef communities.

CAN WE IMPROVE ON THIS?

As anglers we can really only imagine the state of our fish stocks back when the Bay floor was covered with native shellfish and associated life. Looking at the effects of almost two centuries of European settlement it's amazing how resilient the Bay has been and how it continues to support our popular and productive fisheries. Members of the Albert Park Yachting and Angling Club have been using their imaginations, looking at how much better the Bay marine environment could be, with spin-offs for fishing, if oyster and mussel beds could be re-established. Since 2012 they've been working with Fisheries Victoria managers and researchers and with other angling bodies and commercial fishermen to develop a staged approach towards this goal.

Victoria has some excellent resources which if they can be harnessed together could turn the APYAC members' dream into a reality:

•the Bay continues to be a nutrient and plankton-rich "soup", ideal for supporting large masses of shellfish such as oysters and mussels;

•the Government and the EPA view favourably the cultivation of native shellfish that can help in containing nutrient levels as Melbourne grows;

•DEPI's Queenscliff commercial shellfish hatchery has a proven capability of producing large quantities of oyster and mussel spat that could be used to seed new beds in the Bay;

•the Recreational Fishing Licence currently brings in $7 million annually of which $3.4 million was invested in recreational fisheries projects in 2012/13 - to date, the grants program has had difficulty identifying and attracting substantial marine fish habitat improvement projects with clear benefits to recreational fishers.

In 2012 the APYAC succeeded in applying for RFL funding for the first step towards growing natural shellfish reefs in the Bay. The project had two major components. First, the Club invited anglers, commercial fishermen and agency people with knowledge of the former distribution of shellfish reefs to share their knowledge at a workshop held at the Bayside club-rooms in November 2012. That information was overlain on large-scale charts. The second component was contracted to DEPI fisheries scientist, Dr Paul Hamer, who reviewed published and unpublished information on Bay shellfish and on the prevalence of likely oyster and mussel predators and competitors. This plus the workshop information helped him to define potential sites for the next phase of the project - a trial placement in up to three locations of juvenile shellfish cultured at the Queenscliff hatchery. Paul also reviewed overseas experience with similar projects.

The results of this first-stage project was a report Towards reconstruction of the lost shellfish reefs of Port Phillip Bay, written principally by Paul Hamer with input from Ross Winstanley and the APYAC's Bob Pearce. This report describes a "framework to guide the implementation of a shellfish reef restoration program" along with suggested sites and a design, with costings, for a large-scale trial project. It also outlines the common history of destruction of oyster reef habitat in major embayments and estuaries in the USA and Europe. These losses are usually attributed to over-fishing and varying combinations of disease, pollution, exotic species and the loss of hard substrate for resettlement of oyster spat. In turn, losses of oyster reefs have invariably flowed on to damages to fisheries, water quality and ecological health in these waters.

Improved understanding of the importance of shellfish reefs in temperate waters has led to the comparison of their ecological role to that of corals in tropical waters. This has stimulated highly successful shellfish reef restoration projects - some on a very large scale - that have reversed the losses in both environmental and fisheries terms. In many cases these projects have featured outstanding collaboration between fisheries and other marine/environmental agencies and Non-Government Organisations along with community groups, fishers, universities and private industry.

The aim of these overseas projects has varied from re-establishing lost shellfish fisheries, rehabilitating damaged scale-fish fisheries, managing excessive nutrients and stabilising coastal erosion. During May 2014, three US-based and one Melbourne-based members of The Nature Conservancy met with Fisheries researcher, Dr Paul Hamer, APYAC members and a Melbourne University marine scientist to discuss the feasibility of a shellfish reef reconstruction program for the Bay. They dived at several locations in the Bay and met with APYAC and Fisheries Victoria and concluded that this concept is, indeed, realistic.

REALITY CHECK

Clearly, there have been major environmental changes since the days when oyster and mussel reefs and scallops covered most of the Bay. As those changes can't simply be reversed by installing hatchery-produced shellfish, some regions are not recoverable. Large areas of the Bay are now subject to periodic channel/harbour dredging, dredge spoil disposal or regular inundation with sediments. The absence of suitable hard substrates and the presence of predators and competitors - both native and exotic - are limiting factors that apply to much of the Bay. Some of these factors can be compensated, for instance by the placement of hard substrate material that is suitable for settlement of oyster and mussel spat. All of these risk and limiting factors have been assessed in the "Towards reconstruction ..." study.

WHY INVEST IN SHELLFISH REEFS?

Spasmodic artificial reefs projects in the Bay during the 1970s and 1980s excited anglers' imaginations for a time but were extremely localised and mainly short-lived in their effectiveness. The more systematic approach taken by Fisheries Victoria and anglers since 2009, funded from the Recreational Fishing Licence grants program, has seen purpose-built reef units installed at several locations to enhance catches by boat and pier based anglers. While effective in their intended purpose - attracting popular species such as snapper - these "Recreational Fishing Reefs" do little to replace the natural shellfish reefs and bottom communities that have been lost. In short, they can't replicate themselves - shellfish can.

The motive behind the APYAC's shellfish reef renewal initiative is - as far as possible - to see the environmental condition of the Bay returned to how the older Club members can recall it 50 years or so ago. While their particular interest is in Hobsons Bay where their members usually fish, they are not particularly concerned with increasing fish catches. Nor are they concerned by the fact that any catch benefits may be shared by commercial fishermen.

The plan is that successfully reconstructed shellfish reefs on a broad scale will come to provide the foundation for self-sustaining bottom communities that enhance fish populations for the benefit of the whole community and future generations. As oysters, mussels and similar bottom fauna act as large-scale water filters, they play a critical role in removing excess nutrients and other contaminants on an ongoing basis. Improved water quality and overall environmental health will enhance the quality of seafood produced by recreational and commercial fisheries and shellfish aquaculture in the Bay - everyone wins.

Right now this is a vision but it's one that is reachable through a practical step-wise approach and has absolutely no down-side. The immediate challenge is to project this vision in a way that can capture the imaginations of the wider fishing community and all other users of Port Phillip Bay.

Looking beyond Victoria, a national Fisheries Research and Development Corporation (FRDC) project has pointed to the restoration of shellfish reefs in 'large embayments' as a priority for improving fisheries productivity, nutrient cycling, bottom stability and robust seafloor communities. As Fisheries Victoria's researchers are linked in with this project, investment in the next steps towards the APYAC's goal will be part of a high-level movement bringing community, industry, scientific and investment resources to bear on bays from Queensland around southern Australia to south-west Western Australia.

WHAT DOES THIS MEAN FOR ANGLERS?

In inland waters there seem to be endless opportunities for RFL-funded habitat restoration projects with the potential for lasting benefits for fish and for recreational fishing. Angling bodies, Catchment Management Authorities and others have a great and continuing track record in stream habitat improvement works that benefit fishing without compromising other uses. These include re-snagging, willow removal, streamside fencing and revegetation, fishways and stream-flow modification structures. Since 1999, over $2.5 million of RFL funds have been used to leverage a far greater investment in these inland waters projects.

In marine waters it's not so easy to find genuine fish habitat restoration projects. The only investment that comes close is the $1.3 million of RFL funds spent on recreational fishing reefs in bay and offshore waters and temporary Fish Attracting Devices (FADs) which serve to attract fish, not to improve or restore quality highly productive fish habitat. This shellfish reef restoration project offers anglers the opportunity to invest in lasting environmental improvements to Bay that supports their premier marine fishery.

WHERE NEXT FOR THIS PROGRAM?

The APYAC has a current application in with Fisheries Victoria for funding the next stage in this project from the RFL Grants Program. Whether or not this is successful in 2013 there's a momentum already building up with a wide group of potential collaborators and co-investors. It seems just a matter of time - how and when it proceeds.

The report Towards reconstruction of the lost shellfish reefs of Port Phillip Bay by Paul Hamer, Ross Winstanley and Bob Pearce (December 2013) is a Recreational Fishing Grants Program Research Report and can be found on the DEPI Fisheries Victoria web site www.depi.vic.gov.au/fishing

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