Mapping and characterisation of key biotic and physical attributes of the Torres Strait ecosystem: CRC-TS task number: T2.1 final report

The Torres Strait Protected Zone (TSPZ) is a unique area of ecological and cultural significance, shared under an international treaty with Papua New Guinea. As a joint management area, activities such as commercial fishing and traditional hunting occur with primary natural resource conservation goals. Managers need information on habitats and biodiversity distribution and risks to ensure these activities are conducted sustainably. However, while broad seabed habitat information was available for much of the TSPZ from past projects, there were significant gaps and very limited species level data. From 2003 to 2006, the Torres Strait Mapping and Characterisation Project has mapped habitats and their associated biodiversity across the length and breadth of the Protected Zone to provide information that will help managers with regional planning and to ensure that fisheries are ecologically sustainable, as required by environmental protection legislation.\ud \ud Comprehensive information on the biodiversity of the seabed was acquired by visiting almost 200 sites, representing a wide range of known environments, during two 1-month-long voyages on two vessels and deploying several types of devices such as: towed video and digital cameras, an epibenthic sled and a research trawl to collect samples for more detailed data about plants, invertebrates and fishes on the seabed. Data were collected and processed from ~100 km of towed video and >10,000 photos, and from sorting and identification of ~2,000 benthic samples, ~1,200 seabed fish samples, and ~200 sediment samples. The project has analysed this information and produced all of the outputs as originally proposed; these included:\ud \ud • Images and videos of seabed habitat types and fishes, including more than 120 substratum and biological habitat component types. An inventory of more than 3,600 species of benthos, bycatch and fishes, with catalogued museum voucher specimens, many of which were new species, and a database of almost 25,000 records of species distribution and abundance on the seabed.\ud \ud • Identification of the key environmental variables likely to be important in structuring seabed distributions, and predictive models of bio-physical relationships between seabed species, their assemblages and the physical environment.\ud \ud • Maps of the distribution and abundance of ~250 seabed species throughout the TSPZ region.\ud \ud • Estimates of the likely extent of past effects of trawling on benthos and bycatch over the entire TSPZ region, which indicated that trawl effort had a significant effect on the biomass of 8.2% of ~250 species mapped; with negative change of -3% to -18% for 3.5% of species and positive change of +3% to +63% for 4.7% of species.\ud \ud • Estimates of exposure to trawl effort showed that about 80% of the ~250 species mapped had low or very low exposure, and at the other extreme about 21 species had moderate-high to very-high exposure - of these species, after taking relative catch rates into account, six had moderate-high to very high estimates of proportion caught annually and 13 had moderate-low. The remainder (237) had low or very low estimates of proportion caught annually.\ud \ud • Indicators based on qualitative recovery ranks showed that about 9 species stood out as being at higher relative risk. Another, additional, quantitative absolute sustainability indicator showed that one species exceeded a limit reference point while three others exceeded one or two conservative reference points. Another 10 species were also listed due to uncertainty in parameters though they were below the sustainability reference points. Further research is recommended to address key uncertainties in estimates of these indicators.\ud \ud A key output from the project is the identification, by means of the trawl exposure and sustainability indicators, of species at risk or potentially at risk from trawling. Different species were highlighted by different indicators, though there was some overlap. One indicator was both quantitative and directly related to sustainability, with biologically based reference points - while one species appeared to be at risk and another three species exceeded conservative reference points, there is uncertainty that requires a more precautionary response. Hence, the top ranked species for all indicators were listed and recommended to be considered for stakeholder consultation regarding future action; options may include clarification of the identified uncertainties, monitoring of species at risk, and management interventions that reduce risk or combinations of these actions.\ud \ud It is also recommended that long-term monitoring of trends in ecological condition of identified key seabed habitats and constituent species be implemented to assess responses to regional pressures, including climate change. Candidate habitats should include those that have been demonstrated to be particularly biodiverse such as vegetated areas and epibenthic gardens. The seabed may well be vulnerable to climate change as there is an expectation that the thermocline may deepen and upwellings may become weaker and less frequent, with potential consequences for productive habitat dependent on nutrients from such sources.\ud \ud Further work is needed to address the uncertainties in the risk assessments that arise from uncertainties in estimates of catchability and natural mortality rates. Currently, the uncertainty is such that several additional species could exceed the reference points and many species with unknown mortality might be of concern. It is also possible that clarification of these uncertainties may show that species currently thought to be at risk or potentially at risk may be demonstrated to be of no sustainability concern. Thus, it is recommended that further studies of catchabilities and natural mortality rates be conducted to address this key uncertainty for affected species. Such results are likely to have wide application in risk assessments being conducted in multiple jurisdictions.\ud \ud Many fisheries in Australia are conducting qualitative approaches to Ecological Risk Assessments. However, the results of the more quantitative sustainability indicators applied here raise concerns about the reliability of the qualitative approaches, which have not been benchmarked because of the lack of a suitable test bed. Such a test bed is now available with this Torres Strait seabed mapping and characterisation dataset and an assessment of the performance of the qualitative methods is warranted. This seabed mapping dataset also provides an opportunity to develop condition and trend and vulnerability indicators for seabed communities and ecosystems that are needed to meet the increasing requirement for ecosystem-based management approaches.\ud \ud A follow on project supported by the Marine and Tropical Science Research Facility is quantifying visible species from the available towed camera video to fill significant gaps in areas that were too rough for sampling and are currently lacking species information.\ud \ud Another project supported by the Commonwealth Environment Research Fund National Marine Biodiversity Hub will use the Torres Strait seabed mapping dataset in comparisons with other datasets to test the inter-regional utility of physical variables and cross-taxonomic patterns as surrogates for application in marine planning at a national scale.\ud \ud Other further opportunities include: sorting and identification of remaining samples that could not be completed within the scope of the project, and taxonomic work to properly identify the more difficult specimens. These activities would provide full utilization of the samples and deliver additional value, with expected benefits for greater understanding of the seabed ecosystem, fishery sustainability, and ongoing regional marine planning