Engineering enhanced fisheries?
Offshore artificial reefs (OARs) are used worldwide to enhance fisheries and are especially popular in Australia and East Asia.?
Research shows that purposefully designed artificial reefs produce up to 4 time more fish than natural reefs. Artificial reefs provide habitat for marine organisms, provide food and shelter for fish, enhance biodiversity, and attract sustainable fishing and tourism activities.??
This is now the second time SeaO2 have taken the challenge of delivering OARs for NSW DPI Fisheries; making a total of 6 installed reefs over 3 sites: Batemans Bay (Eurobodalla), Terrigal and Forster?
How do we maximise the impact of this project with the funding available??
The answer lies in an ‘engineering orchestra’ that performs over 4 different phases to deliver this ambitious project:??
Design -> Fabrication -> Transport -> Deployment?
Design?
This phase is the foundation of the project. It incorporates a combination of marine biology, engineering, logistics, and seamanship.?
Here starts the design spiral, associated with a long list of question.??
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The key and answers to all those questions was a well-coordinated “orchestra” including marine scientist, naval architect, ocean engineer, steel fabricator, and tug master; each keeping front of mind the goal of maximising the biological outcome.??
Terrigal and Forster Offshore artificial reefs are located several kilometres offshore in 30-40m of water, which adds a layer of risk and complexity to the project. To mitigate this risk, we decided to use a tow and sink method, which has a significant impact on the design, as the reef incorporates sacrificial buoyancy chambers.?
Following the recommendations of our marine ecologist, the base structure was enriched with numerous features to provide a complex habitat for fishes to feed, rest, hide, hunt and breed, including distinctives area for benthic and pelagic communities.?
The reefs create areas of shade and upwelling of current flows, while being semi-permeable in design to ensure migrating sand waves and sand-induced movement from storms and wave action can pass through modules, rather than building up against them.?
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Fabrication?
Our design ‘foundation’ has been laid and double checked by a third party on behalf of the client; fabrication can now start.?
For Terrigal and Forster, the equivalent in weight of 20 x buses is prefabricated then “flat packed”. Before being transported, through a coordinated logistic effort, to our assembly site in Sydney Harbour.?
After few weeks of assembly and welding work at scale (like a giant Ikea set) the reefs starts to appear whole and reveals their impressive size.?
Testing is completed to validate the integrity of the finished reefs;?
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Transport to site?
Each Reef now needs to be moved from its assembly area up to the wharf edge. This is done using a “Float” truck; this trailer-of-sots is typically used for massive, over-sized freight that is over legal height, width, weight, or a combination.?
From the float truck, the steel structure is lifted by a 300T crane barge and launched into the water.?
Once in the water, a series of hydrostatic checks are carried out before the reefs are taken to a standby mooring.?
Cooperation with nature starts and long-range weather forecast are used to target desired towing and deployment conditions: light wind and small swell.?
A 3-day tow is needed to reach Forster from Sydney harbour. The reef is towed by an experienced tug master along the coast up to the deployment site.?
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Deployment?
On D Day, it’s time to hand over these bespoke reefs to the fishes.?
20 minutes before the deployment a Marine Animal Observer checks that there is no activity within 300 m of the deployment vessel.?
The experienced tug master in coordination with naval architect, positions the reef to arrive on the ocean floor at its exact coordinates, taking into consideration wind and current drift. (Noting: The relative positioning of the 2 reefs at each site is designed to realise the maximum biological synergy from the structures).?
Whilst each reef is held in place by the tug, divers climb on board the still floating reefs to operate the venting valves and sink the reef in a controlled and safe manner.?
92 sec later the reef touches down the seabed!?
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An underwater remote operated vehicle (ROV) is sent down to visually confirm that the reef is upright and stable without damage to the structure.?
It’s now just a matter of time before the first fish to settle around the reef and biofouling grows to cover the structure.? In 6 to 8 month the reefs will achieve full biological productivity.?
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For more information get in touch!?