Putting potential environmental risk of Australia's trawl fisheries in landscape perspective: exposure of seabed assemblages to trawling, and inclusion in closures and reserves
Australian fisheries, including trawl fisheries, need to ensure they met legislative requirements to ensure they have no unacceptable impacts on ecosystems. Linked to this need, the annual Status of Australian Fish Stocks (SAFS) reports are intended to include broader environmental reporting including indicators such as the “habitat footprint” of fishing.
CSIRO has been assisting AFMA to meet these requirements, recently taking into account new data & methods — and new management — to implement a consistent spatial approach to mapping demersal ‘assemblages’ & applying it to Commonwealth bottom trawl fisheries (FRDC 2014/204).
There is a need to extend this approach to all continental shelf trawl fisheries, in collaboration with researchers in each State, to meet assessment & reporting requirements and deliver benefits to all jurisdictions. Most of the data required are available & ready to use for the purpose, with some new data to be collated; the methods are now established & successfully demonstrated, hence the work can be completed cost-effectively. Further, the ecological maps provided by national assemblages mapping can be used as a spatial framework to underpin similar footprint assessments for other fisheries & offshore industries.
These needs have been identified at a recent (Feb 2016) ‘FRDC Key Projects Workshop’ to develop a strategic plan for delivery of FRDCs Priority 1: “Ensuring that Australian fishing & aquaculture products are sustainable & acknowledged to be so”.
Final report
This project implemented the first national spatial approach to quantifying the exposure of mapped seabed assemblages to the footprints of all demersal trawl fisheries that operate on the mainland continental shelf and slope of Australia, as well as their spatial protection in areas permanently closed to trawling. These outputs will assist understanding of the potential risk to demersal assemblages from exposure to trawling footprints and of the contributions of existing spatial management measures to environmental sustainability, and with identifying and prioritising future needs for addressing risks to habitats. The focus provided by this prioritization is intended to reduce the costs of environmental assessments, and ultimately facilitate outcomes including reduction of the ecological risks posed by trawling and improved environmental sustainability. Trawling footprints were mapped from fishery effort data for recent years. Protection provided by current spatial management included all permanent trawl‐fishery closures, the Commonwealth Marine Reserve system (CMRs) and State Marine Protected Areas (MPAs). Seabed assemblages — as surrogates for broad habitats — were defined and mapped using a single consistent method that has been enabled by recent advances in analysis methods and the availability of new data and knowledge. The overlaps of each assemblage with trawl footprints, and with areas closed to trawling, were calculated to quantify trawl exposure and spatial protection.
The majority of the 217 seabed assemblages defined and mapped had little or no exposure to trawling by the State and Commonwealth trawl fisheries included in the assessment. These assemblages with low trawl exposure also included a large number with little or no protection in any areas closed to trawling, in addition to those with higher levels of protection in closures. Across all fisheries, there were relatively few assemblages that had both high exposure to trawling and low protection by closed areas. Several more highly exposed assemblages also had substantive inclusion in closed areas. For example, 15 assemblages had >30% trawl footprint exposure (maximum footprint = 64.4%), of which 5 had >20% protection (max 37.5%) in areas closed to trawling. Assemblages with low exposure and high protection may warrant less focus for future habitat ERA. Assemblages with both high exposure and low protection are considered higher priority for future habitat ERA focus. These include assemblages along much of the Australian east coast from southern Queensland including deep areas of the southern GBR, through shelf areas of NSW, to eastern Victoria/Bass Strait — as well as western Tasmania to SE South Australia on the upper slope, inside Shark Bay, and near the shelf break in the Great Australian Bight. The identification of these trawl‐exposed assemblages reflects potential rather than confirmed risk to habitat; information on the distribution of sensitive habitats, habitat‐forming benthos or vulnerable species in higher priority assemblages is required to make such a risk assessment. However, such information is lacking in most priority assemblages — and in cases where some information is available, the presence of sensitive benthos and/or vulnerable species is indicated, thus raising the likelihood of actual risk, but currently the data are inadequate for comprehensive assessment of their status or risk. The current lack of adequate data needs to be addressed to achieve and demonstrate sustainability.
It is likely that the majority of demersal assemblages within Australian trawl fishery jurisdictions are not subject to substantive risk from these fisheries, due to their low exposure, and this is largely independent of whether assemblages have high or low protection. The relatively few assemblages within these jurisdictions that have higher exposures to trawling have high potential for risk to sensitive habitats and vulnerable species if they occur in these areas. Thus, the limited resources for future habitat ERAs can be focussed on the small number of more highly exposed assemblages, particularly those with lower levels of protection, that need further investigation to assess whether sensitive habitats and/or vulnerable species are present and whether they are at substantive risk from demersal trawl or dredge fishing. This focus will enable more efficient application of resources on ERAs for habitats. Ultimately, expected benefits include reduction in environmental risks due to trawling, management agencies meeting requirements of legislation regarding environmental sustainability, and hence improved social licence for fisheries. The recommended future research to assess actual habitat risks is essential to achieving these ultimate outcomes.
