2015-11-10 - P&O Agenda - Item 7, Attach 2 - Assessment of Oyster Recruitment

2 Methodology

2.1 Survey Area – Noosa River Catchment
The Noosa River Catchment covers 841 km2 and is within the Noosa Drainage Basin. The
Noosa River flows south from its headwaters in the Cooloola Section of the Great Sandy
National Park to the ocean, north of Noosa Headland. The river is spring fed from major sand
deposits and has continuous freshwater flows. Noosa Estuary is a Holocene Tidal Delta,
dominated by soft sediments, with several shallow lakes (Cootharaba, Cooroibah, Doonella,
Weyba) throughout the system, the largest of which is Lake Cootharaba (Figure 1).
Estuarine habitat has been mapped upstream of Lake Cootharaba, although depending on
the flow of freshwater, salinity is typically low in these lakes. The sediments in the estuary
consist largely of undifferentiated deposits of lagoonal and estuarine sands and muds, and
coastal muds including muds incorporated into mangrove sediments (Lloyd 1980). The
Catchment has a subtropical climate, which receives on average 1600 mm of rainfall
annually. Temperatures range from 22 to 28°C in Summer and 11 to 21°C in Winter (BOM
site 040908 Tewantin RSL Park – averages based on data collected from 1994 to 2014).
Tides in the estuary are semi-diurnal with a tidal range of 1.4 m at the mouth, decreasing to
0.9 m at Tewantin (Stephens 1973). During spring tides, tidal currents can reach 2.5 knots in
the main river channel (Stephens 1973).


2.2 Approach
Settlement tiles (10 cm x 10 cm squares made from fibrous cement sheet) were deployed at
seven intertidal (0.1 m above low water mark) and five subtidal sites (typically 1 m below the
surface) around the Noosa River Estuary (Figure 1 & Table 1) to determine the potential for
recruitment1 of oysters at different depths and surface orientations. At each site, the
settlement tiles were deployed in an array of 4 replicate tiles in two different orientations
(vertical and horizontal) and secured to a cement block (Figure 2a,b).




1
  Recruitment is defined as the point at which the pelagic (swimming) larvae of oysters settle out of the water
column onto another oyster shell or other hard surface and survive long enough to be counted in the population
(sensu Hunt & Scheibling 1997)


Restoration of Noosa Estuary: An Assessment of Oyster Recruitment                                                 3