Can bottom trawl fishing be sustainable in Australia?

The release of Ocean with Sir David Attenborough has provided an informative and confronting glimpse into some of the realities of the global fishing industry. In particular, footage of bottom trawling in Turkish waters and scallop dredging in UK waters, both taken under permit during the production of the film, have raised concerns about these fishing methods across the globe. So how do they relate to our Australian context?

Bottom trawling is among the highest impact fishing methods employed in Australian fisheries, though with careful management these risks can be reduced to an acceptable level. AMCS and leading Australian trawl fisheries have been working hard over decades to this end, though serious challenges remain. Whilst not all trawling is bottom trawling, in this blog, we’re diving into the details of bottom trawling in Australian fisheries.

What are the issues in Australia?

Habitat 

Bottom trawling can damage sensitive seabed habitats such as sponge gardens, deepwater reefs, seagrass meadows and seamounts. In Australia, the CSIRO has extensively mapped the seabed providing a good knowledge of biodiversity and sensitive habitats, such as within the Great Barrier Reef Marine Park (1). The CSIRO and fishery management agencies also monitor the trawl footprint – the area over which trawling occurs – and have studied the amount and level of bottom trawling in sensitive habitats (2). From this information, we know that trawl operations can limit habitat impacts by avoiding and protecting sensitive habitats, and trawling previously trawled areas — a principle known as ‘trawling on the trawl footprint’. 

The Australian bottom trawl footprint is generally smaller than many international fisheries. However, some fisheries still include highly sensitive and biodiverse habitats totally unsuited to trawl fishing. The Australian State of the Environment Report (2021) finds that most seafloor habitats are in good condition, but some habitats, particularly in temperate eastern and southeastern Australia which are intensively bottom trawled, are in poor condition (3). Habitat protection can help, but with the exception of a few areas of our coast, most Australian habitats at present have inadequate protection within marine parks. 

While some habitats are totally inappropriate for bottom trawling, others that are subject to natural disturbance (by waves or currents) like sandy bottom areas are quick to recover from trawling and can be managed effectively (4). For example, western king prawns caught in South Australia’s Spencer Gulf are caught using an otter trawl fishery which avoids sensitive habitats. The fishery has worked to reduce its footprint by around 75% while maintaining catches – significantly reducing its impact. It’s the first and only trawl fishery to be green-listed in our GoodFish Sustainable Seafood Guide and we’re proud to recommend Spencer Gulf western king prawns to our partner chefs and supporters. 

In stark contrast, orange roughy are caught by bottom trawling over ancient and extraordinarily vulnerable deep-sea coral reefs on seamounts in southern Australia and are red-listed in our GoodFish Guide. Corals on these reefs can be thousands of years old, and evidence suggests they take decades, if not centuries, to recover (6). Entire reefs have been destroyed by bottom trawling for orange roughy (7). Despite this, the Australian government is allowing orange roughy trawl fishing to expand. The government is even permitting exploratory fishing in areas closed specifically to protect deep sea biodiversity. Orange roughy fishing is likely the most destructive form of fishing allowed in Australia, and one of the most destructive bottom trawl fishing activities globally.

Bycatch

Bycatch refers to the unintended capture of non-target species during fishing operations which are subsequently thrown back dead or alive. In trawl fisheries, particularly bottom trawls, bycatch is a significant issue. As nets are dragged across the seabed, they often capture a wide range of marine life beyond the target species. In most Australian bottom trawl fisheries, bycatch is the key factor determining sustainability, with tropical prawn trawl fisheries typically responsible for the highest rates (8).

In Australian bottom trawl fisheries, common bycatch includes:

• Small fish and juvenile target species
• Non-target crustaceans and invertebrates like crabs and squid
• Seahorses and pipefish
• Sea snakes
• Sawfish
• Other small sharks and rays

The volume of bycatch can be confronting. The impact of a fishery’s bycatch depends on the species and quantity caught. Some species are considered to be at relatively low risk from bottom trawling, often because they don’t face other major fishing pressure.

In some Australian bottom trawl fisheries, certain non-target species are permitted to be retained and sold, known as ‘byproduct’. This can reduce waste as much of the fish and invertebrate bycatch often dies in the trawl nets. 

Yet in several major trawl fisheries, bycatch includes severely overfished species and many where population health is poorly understood. 

Bycatch is a key threat to many threatened and protected species, including several small sharks and rays that are threatened and found only in Australia. In tropical fisheries such as the Northern Prawn Fishery or Queensland’s East Coast Trawl Fishery, thousands of sea snakes and hundreds of sawfish are caught each year (9, 10). 

Bottom trawling adds to the cumulative impacts these species face from climate change, habitat degradation, and other fishing methods like gillnetting. Many are long-lived, reproduce slowly and have relatively few offspring, making them especially vulnerable. 

Without robust independent reporting of fishing activity, such as electronic monitoring (i.e. cameras on boats), catches of threatened and protected species are often significantly under-reported.

The good news is that many Australian bottom trawl fishing industries have shown willingness to innovate. Bottom trawl fisheries have substantially reduced their impacts on turtles, and some have been able to reduce their impact on sea snakes and seahorses considerably.

What changes has the fishing industry made?

Over recent decades, the bottom trawl industry has made significant changes to improve sustainability. This is due to public pressure, increased scientific knowledge, conservation efforts and industry leadership.

• Turtle Excluder Devices (TEDs): Now mandatory in tropical prawn trawl fisheries, TEDs were introduced in the early 2000s to allow turtles and other large animals to escape the net. Their introduction dramatically reduced turtle and large animal (like sharks) capture, meaning these fisheries are no longer considered a high risk to turtles. 
• Bycatch Reduction Devices (BRDs): A variety of BRDs have been introduced to reduce the capture of smaller bycatch species including non-target fish, invertebrates, and threatened species like sea snakes and rays.
• High-resolution Vessel Monitoring Systems (VMS): Mandatory in most Australian bottom trawl fisheries, VMS tracks vessels in real time using GPS, helping enforce closures like marine parks and limits on how much trawling (i.e. ‘effort’) is allowed.
• Smaller footprint: Australia’s bottom trawl footprint is relatively small and closely monitored, particularly in the Northern Prawn and Queensland East Coast Trawl fisheries.
• Fleet size: The number of bottom trawl boats and their corresponding fishing effort has declined considerably in recent decades (11).
• Line trawling: Used in the Queensland East Coast Trawl Fishery and some other fisheries, this method of trawling involves repeatedly trawling the same line restricting trawling to consistent tracks, minimising trawl footprint and seafloor disturbance. 

These changes show that some of bottom trawling’s risks can be mitigated with strict management and innovation.

What still needs to be done?

Bottom trawling can be sustainable in Australia, as is shown by South Australia’s Spencer Gulf Prawn Fishery being the first bottom trawl fishery green listed in our GoodFish guide. However, for other bottom trawl fisheries, further work is required and serious sustainability challenges remain. 

Australian bottom trawl fisheries have introduced a range of improvements over the past two decades. However, serious sustainability challenges remain. Bottom trawling in some fisheries continues to destroy ancient deep-sea coral reefs, threaten endangered species, and impede the recovery of overfished species. AMCS works with industry and fisheries management to address these issues and ensure that trawling is done more sustainably:

Electronic monitoring: There are widespread concerns that threatened species interactions are under-reported in some bottom trawl fisheries. Independent monitoring via scientific observers or cameras provides accurate data on catch and bycatch, showing what is caught and where. For many fisheries, cameras are the more cost-effective option. Accurate data is essential to help threatened species recover and ensure fishery’s aren’t a high risk to our iconic wildlife. 

Further reductions in threatened species bycatch: Sea snakes, sawfish, several endemic sharks and rays, and other threatened species are still caught in some bottom trawl fisheries, and additional mitigation strategies are needed. This could include the innovation and adoption of new lower impact fishing gear, BRDs or protection of critical habitats for some species. 

Marine parks and spatial management: Australia’s oceans are underprotected, including in some habitats with high exposure to bottom trawling. Australia’s temperate eastern and south-eastern waters are particularly heavily trawled and poorly protected. Networks of strong marine sanctuaries, acting like national parks in the ocean, are essential to safeguard marine life. Marine sanctuaries also help previously impacted areas recover, including sensitive habitats that have historically been bottom trawled. The Australian government must expand our network of marine sanctuaries to safeguard marine life for generations to come.