The map of Macquarie Harbour in Figure 1 shows the location of the WHA boundary within the harbour, the marine farming leases and a range of monitoring sites where data are either collected by the Environment Protection Authority (EPA) or reported to the EPA by industry. The three salmon companies operating in the harbour undertake video monitoring surveys as part of their marine farming licence requirements. Additional research (eg by IMAS, CSIRO, EPA and private consultants) is investigating the decline in dissolved oxygen levels in the water column and deteriorating benthic conditions within the harbour. Visual monitoring using remote control video is undertaken at compliance points (at 35 m and subsequent distances from the lease boundaries) and at 19 control sites across the harbour, ten of which are within the WHA.
Figure 1 Map of Macquarie Harbour monitoring sites and WHA boundary (Source: Macquarie Harbour Tasmanian Wilderness World Heritage Area Environmental Status Report, May 2017)
The underwater video footage gives a visual indication of the condition of the harbour, using the presence of the bacteria Beggiatoa spp. on the benthic sediment surface as the key parameter reported. Beggiatoa spp. is a naturally occurring organism, present in circumstances of low dissolved oxygen where it breaks down (feeds on) decaying plant and animal material. Its presence, therefore, is used as a general indicator of a low oxygen environment.
Video Monitoring Results
The video files below provide a snapshot of raw data collected at four survey sites within the WHA in September 2016, along with a survey conducted at one of those sites in May 2012. The data from Location 39 (close to the WHA boundary) in May 2012 provides baseline data prior to the expansion of marine farming in Macquarie Harbour. The surveys sites 39, 42, 43 and 44 are situated in a line reaching from the WHA boundary (adjacent to lease 266) towards the entrance of the Gordon River. They provide a comparison of benthic impacts due to several factors, including both marine farming at sites closest to the WHA boundary and freshwater nutrient loads at sites closer to Gordon River.
Video survey, May 2012, Location 39: Silty brown sediment with a few Sabellid fan worms, shrimp, gobies and urchins. No Beggiatoa.
Video survey, September 2016, Location 39: Silty brown sediment with numerous individual Dorvilleid worms (Schistomeringos lovenii) visible as white worms and a few Terebellid worms. No Beggiatoa.
Video survey, September 2016, Location 42: Silty brown sediment with numerous Sabellid fan worm tubes, no fans visible; some urchins and urchin tests, and a Terebellid worm. No Beggiatoa.
Video survey, September 2016, Location 43: Silty brown sediment with isolated dark patches, numerous individual Dorvilleid worms of mixed morphology, cerianthid spp, few terrebellids, mounds, burrowing, few heart urchins. Patchy Beggiatoa.
Video survey, September 2016, Location 44: Silty brown sediment. Few individual mixed morphology Dorvilleid worms. Bioturbation evident in sediment, heart urchins, worm tubes, goby spp. Patchy Beggiatoa.
Note: Although the survey methodology requires 3 minutes of continuous recording of benthic video footage, the attached videos have been edited to 15 seconds of continuous representative observations.
The presence of Beggiatoa spp. in the WHA reflects a decreasing oxygen environment and the presence of an organic load. It is evidence of deterioration in the environmental condition within the harbour, primarily due to low levels of dissolved oxygen adjacent to the harbour floor and in the mid-water regions. However, these observations do not indicate the source of the organic matter or the drivers of the environmental conditions which have led to Beggiatoa spp. presence, nor a complete picture of potential impacts from various sources.
The September 2016 WHA control point video surveys taken at locations 43 and 44, which are several kilometres upstream from the WHA boundary and closer to the confluence of the Gordon River, showed patchy Beggiatoa spp. Meanwhile, locations 42 and 39, which are situated closer to the WHA boundary (and Lease 266), showed none. Lease 266 was non-compliant in September 2016 with patchy Beggiatoa spp. reported as extending up to 1 km from the lease boundary towards the WHA. In response to this non-compliance and the likely impact on the WHA, the EPA required Lease 266 to be fully de-stocked, which was completed by 10 April 2017. Subsequent monitoring in March and April 2017 has indicated that the extent of Beggiatoa spp. around this lease has contracted substantially and is now well outside of the WHA boundary.
So, while marine farming is likely to be a factor in reducing dissolved oxygen within the harbour, other drivers also exist, including organic load from freshwater inputs. Beggiatoa spp. was first observed at two WHA control sites (locations 43 and 58) in September 2015 and by September 2016, it was reported as being present (‘patchy’) at five of the ten WHA monitoring sites. In the most recent January 2017 surveys, the observations have been of faint, patchy Beggiatoa spp. at seven sites, with a thin mat observed at site 45, closest to the Gordon River, in January 2017.