Effects of trawling

The challenge

Balancing community and economic benefits with environmental sustainability

Trawl fisheries provide an important component of Australia and the world's, nutritional needs and economy. As the global population continues to increase, the need for seafood grows with it.

Management of trawl fisheries must ensure they are sustainable, continuing to provide seafood, jobs and economic benefits into the future while preventing unsustainable impacts on the environment.

Our response

Supporting management decisions with seabed assessments

CSIRO works with governments, industries and communities to understand the direct effects and extent of trawling on seabed ecosystems.

Our research evaluates the consequences of trawling at regional scales and the effectiveness of different management measures.

The approaches we have developed are being applied to other trawl fisheries in Australia and overseas, including:

• experiments that quantify trawl impacts on different seabed biota
• monitoring of recovery rates of sensitive biota after trawling
• studies of trawl bycatch, devices to reduce bycatch, and bycatch risk assessment 
• surveys and mapping of regional distributions of seabed habitats & biota
• simulation modelling of trawl fisheries, impacts and management to assess seabed status and compare alternative management actions
• building of comprehensive national databases of seabed biota distributions and trawl fishing effort across Australia
• quantification and mapping of trawl footprints and intensity regionally and Australia-wide
• mapping of national seabed assemblages and regional seabed invertebrate communities to quantify exposure of seabed biodiversity to bottom trawling and protection in reserves & fishery closures
• development of quantitative models for risk assessment of trawling, including simpler methods that can be used in data-limited situations

The results

Trawl impacts are being managed, although areas of future focus remain

CSIRO research provides evidence to support management decisions that improve the sustainability of trawl fisheries.

Our research shows that:

• many seabed biota are relatively unaffected by the direct impacts of trawling, however some are affected, particularly more sensitive types
• most biota can recover in a few years, but longer-lived sensitive species may take many years or even decades to recover
• many sensitive seabed species naturally occur in habitats where trawling typically does not occur
• trawls catch many non-target bycatch species that are discarded; devices can help reduce bycatch; and assessments show most bycatch species have low risk — however, a few fish species and some sharks and rays have higher risk
• in fisheries we assessed, the abundance of most biota in regions with trawling was above 90 per cent of that expected if there was no trawling; but some sensitive biota had lower abundance 
• management actions in recent decades have reduced trawling effort and closed areas of seabed, leading to recovery in seabed status and reduced risks
• the current Australian trawl footprint is 1.1 per cent of the entire continental Exclusive Economic Zone (EEZ), where a state has special rights regarding the exploration and use of marine resources. 54.8 per cent of the EEZ is protected from trawling by closures and reserves
• trawling in Australia occurs on the shelf and slope, shallower than 1,500 m depth, where the trawl footprint is 3.4 per cent and 37.9 per cent is protected
• regions with the highest trawl footprints are in eastern and southeastern Australia; where several seabed assemblages have high trawl exposure (>30-65 per cent footprint) and are priorities for detailed assessment of habitat risk
• most regional seabed invertebrate communities around Australia have higher protection (average 38 per cent) than exposure to trawling (average seven per cent).

Outcomes include:

• new methods to quantify seabed status and assess risks of trawling, including in data-limited situations world-wide
• understanding of the landscape-scale extent and consequences of trawling in Australia
• supporting implementation of ecosystem-based fisheries management and reduction of environmental risks
• helping ensure trawl fisheries are ecologically sustainable as required by the Environment Protection and Biodiversity Conservation Act (1999)
• identifying regions and biota that require further assessment of risks from trawling.

Our approaches also contribute to an international project on trawling best practice, are supported by the UN Food and Agriculture Organization and are being adopted by the Marine Stewardship Council to assist with assessments for the sustainability certification of fisheries.