Trial of near shore artificial reefs to enhance pier based recreational fishing
Habitat enhancement is viewed by recreational anglers as an important activity for sustaining and improving recreational fishing opportunities in Victoria. In Port Phillip Bay, there is a small amount of natural rocky reef habitat (less than 1% of the bay's sub-tidal area). The large areas of biogenic reef (i.e. reef made of shellfish and other invertebrates and algae) that once existed have also been mostly lost over the last century due to a range of impacts (i.e. dredge fishing, chemical pollutants, sedimentation and exotic species introductions). It is thought that production, aggregation behaviour and diversity of recreational fishery species in Port Phillip Bay have been altered by changes to the availability and quality of reef type habitat. Well planned and designed artificial or 'man-made' reef habitat is one option to increasing reef habitat availability at local-scales, and can provide for enhanced recreational fishing opportunities.
This project conducted the first trial of artificial reefs in shallow near shore waters (< 5 m depth) accessible to land-based anglers, in Port Phillip Bay. It follows the earlier trial of deeper water artificial reefs in Port Phillip Bay, and tests the feasibility of using near shore artificial reefs to provide increased fish diversity and improved fishing opportunities for land-based anglers. The trial, importantly also provides an evaluation of the positive and potentially negative impacts of near shore reefs, at a 'low-risk' small-scale, that will inform risk assessment, planning and design of any future application of near shore artificial reefs in Victorian marine and estuarine waters.
This trial of near shore artificial reefs had the primary objectives of:
- Enhancing fishing opportunities for land-based anglers;
- Evaluating the benefits of near-shore fishing reefs to recreational anglers;
- Involve anglers in the planning and evaluation of a localised fishing and habitat enhancement project; and
- Assessing specified ecological risks associated with near-shore artificial reefs in Port Phillip Bay.
The trial occurred at three locations: Altona Pier, Frankston Pier, and the rock wall section of Portarlington Pier. The Portarlington artificial reef was deployed in September 2012, the Altona reef in October 2012, and the Frankston reef in November 2012. At each location approximately 100 reef modules (combination of Reef Balls and Aqua Trees) were deployed as three adjacent sub-reefs of 33 modules each. Initially the modules were arranged to form a series of patch reefs approximately 40-50 m from the fishing platforms. However, after the first year of angler and visual surveys, feedback on snagging issues and tackle accumulation at the Altona and Portarlington sites, where long-casting surf rods are commonly used, guided a modification of the designs that involved moving the central portion of the reef at Altona, and the two end sections of the reef at Portarlington to a distance of 60-70 m out from the fishing platforms. This modification, along with installation of signage, resolved the snagging issue. The Frankston reef was not modified from the original lay-out as there were no immediate indications of enhanced snagging issues at this location. However, despite signage being added, recent follow up discussions with avid anglers at Frankston Pier suggest that a similar modification is warranted at Frankston to reduce angler snagging and tackle loss over the long-term. Because the reef modules are individual units, modification of reef lay-outs is relatively straight forward using divers and air lift bags.
The monitoring and evaluation program involved a control - impact approach, along with a baseline survey of the control and impact sites prior to the artificial reefs being deployed. The 'impact' sites were the sites on which the reefs were deployed and the control sites were nearby similar areas of seabed sediment without reef and nearby natural reef comparison sites. The control/comparison sites were situated approximately 1-2 km from the artificial reef sites. The survey methods included: visual surveys of fish and invertebrate communities, baited remote underwater video (BRUV) sampling, and creel/perception surveys of anglers fishing on the three piers.
The reefs were rapidly colonised by invertebrates and algae and the local fish communities clearly changed in response to the deployment of the artificial reefs. Depending on the locations, at 1-2 years post deployment, there were 4-9 times more species detected at the artificial reef areas after the reefs were deployed, compared to 2-3 times more species detected on the sediment controls and natural reef comparison sites over the same sampling periods. The near shore artificial reef fish community was a mixture of reef and sediment species more typical of a natural patch reef or reef edge community reflecting the patchy nature of the artificial reef design. Three of the top five species that drove the similarity across the three artificial reefs were recreational target species; Australian Salmon, Silver Trevally and Snapper. In particular, juvenile snapper were highly abundant around the artificial reef habitat, particularly the Frankston Pier reef, and Silver Trevally increased in abundance at the Portarlington artificial reef. Further, there were notable aggregations of Calamari squid observed on several occasions at the Frankston artificial reef.
The creel and perception surveys connected with over 500 anglers, and along with follow up phone calls with avid anglers, indicated differing opinions as to changes in the fishing experience after the reefs were created. Support for artificial reefs by pier-based anglers in general was overwhelmingly positive, consistent with previous surveys of boat-based anglers.
Near shore artificial reefs have potential for enhancing local fish community diversity and abundance, and in-turn recreational fishing opportunities. Local context is however important in predicting ecological responses, and designing reefs for species targeting preferences and fishing methods. Importantly, this study showed no major negative or unintended consequences of the artificial reefs in the near shore environment, suggesting that when well-planned and designed, they can be a low risk option for enhancing near shore reef habitat availability at local-scales. While snagging was raised as an issue at some locations, this was relatively easily resolved by reconfiguration of reef layouts, made possible by using individual movable modules. The project outcomes provide a template for future near shore artificial reefs, including design aspects, reef module resilience and ecological responses to artificial reefs deployed in the near shore environment.
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