An environmental assessment of a proposed marine farming zone extension at Trumpeter Bay, South Eastern Tasmania

An environmental assessment of a proposed marine farming zone extension at Trumpeter Bay on the eastern side of northern Bruny Island was conducted in February and March 2014. The site covered 19.61 km² (1960 ha) and demonstrated a depth strata from 30 – 50 m and was orientated in a north south direction. The benthic habitats within the zone assessment area comprised of sand 1926.24 hec (98.24%) and gravel 34.5 hec (1.76%).

Environmental data on substrate type, habitat distribution, bathymetry, and benthic flora and fauna were assessed. The dominant sand substrate was characterised by flat regions with high levels of bioturbation, ripples, drift sponge and shell grit. The video data highlighted a large number of sites hosting New Zealand screwshells (Maoriculpus roseus). The sediment grabs showed that the sand composition ranged from yellow-brown sand to orange-brown sand with pockets of black silt to gravel. Live and dead New Zealand screwshells (Maoriculpus roseus) were found across the whole survey site. Hermit crabs (Paguristes sp.), a squat lobster (Munida haswelli), Polychaetes, one bivalve (Venerupis sp.), live auger shells (Hastula brazieri), heart urchins (Echinocardium cordatum) were identified from the grab samples. The native screwshell, Gazameda gunii, was not observed in any of the sediment grabs. All of the grab samples were odourless.

An interesting feature within the site was the presence of localised depressions and channels in the sediment on both the eastern and western boundaries. These depressions and channels were commonly around 50 – 90 m in with and were on average only 1 m lower than the surrounding seafloor. The sediment composition differed to the surrounding sand as these pockets and gutters were comprised of gravel and coarse sand with shell grit.