November 2020 marked the first anniversary of the Territory Government’s purpose built artificial reefs, and all four sites are flourishing with an abundance of native fish species and sedentary organisms.
Layers of marine growth including soft corals, sea weeds and other organisms are now present on all of the structures, with over 40 different species of fish identified thus far. From footage recorded during Fisheries NT underwater BRUV monitoring, a range of juvenile Lutjanid species, Jewfish and large schools of trevally and mackerel have all been spotted living in and around the reefs.
Recognised as the largest single artificial reef deployment in the southern hemisphere covering an area of approximately 10 hectares the reefs were designed to enhance productivity of marine life, create new reef habitat and enhance recreational fishing opportunities.
he artificial reefs were developed for Territory anglers as part of the Northern Territory Government $50 million investment over five years to improve recreational fishing opportunities.
As a result of the Territory Government’s investment, and consistent monitoring and underwater BRUV recordings supporting the success of the reefs’ growth, the project, managed by DIPL and Harris Kmon Solutions, won two awards including NT Project of the Year at the 2020 Australian Institute of Project Management’s (AIPM) Project Management Achievement Awards which recognise, honour, and promote outstanding achievements in program and project leadership.
Historically, artificial reefs have been constructed using ‘materials of opportunity’, such as decommissioned vessels and ships, concrete pipe and culverts and disused plant machinery.
More recently, artificial reef construction around the world has taken on a scientific focus, with specific consideration given to materials and designs that aim to boost natural productivity and create new habitats. These purpose-built reefs can be engineered for the chosen location taking into account depth, oceanographic conditions and substrate type to provide the optimal habitat preferred by particular fish species.
The Top End reef fields are made up of a total of 118 separate modules specifically engineered combining the best natural reef habitat features and constructed to last up to 100 years. Each module is 4 meters square at the base and stand 5 meters tall weighing a massive 24 tonnes each. Internal caves, cryptic habitat, vertical relief and upwelling of water flow combine to create optimal habitats to support the long-term sustainability of key fisheries. These exciting new fishing areas will also help reduce pressure on existing natural reefs and enhance the productivity of fish stocks.
Prior to design and deployment, physical studies of potential sites were conducted using sediment grabs, Baited Remote Underwater Video Systems (BRUVS) and bathymetric surveys to validate the suitability of each site and to provide baseline data for future monitoring.
While the new reefs attracted fish almost immediately, they are expected to take up to three years to become fully productive habitats. A variety of reef-associated species will benefit from these new reefs, including:
• species that prefer very close contact with reef structures such as black jewfish, cod and coral trout
• species that remain adjacent to the structures, such as snappers and emperors
• pelagic species that visit occasionally, such as mackerel, trevally and tuna.
The attraction of pelagic fish is important to provide greater ‘catch and release’ fishing opportunities for species that are less susceptible to barotrauma, such as mackerel, queenfish and trevally.
Although only just ticking the first year of success, NT Fisheries have no doubt the artificial reefs will continue to flourish for the next 99 years of the project.

Author: Evan Needham