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

       component of the overall biodiversity of estuarine systems and are likely to contribute
       to food webs and provide a filtration function similar to that of commercial oyster
       species. There was also evidence of both crabs and fish utilizing the newly created
       habitat associated with the settlement tiles and structures.

Based on these findings, our recommendations are:

      The Council look to support the establishment of some small scale pilot oyster reef
       restoration projects. These should be treated as experiments, and developed in
       conjunction with a university group, perhaps the University of the Sunshine Coast.
      The most promising location for these pilot reefs is upper Weyba Creek, but the main
       branch near Tewantin would also provide an interesting learning opportunity because
       of the high siltation rates but also high presence of oyster larvae.
      Pilot reef should trial a number of different designs and materials, and include surface
       orientations that maximise overhanging areas to ensure that recruits are not
       smothered by sediment and algal growth. Pilot reef should be located in an area
       where it will not interfere with normal vessel movement through the estuary (i.e.,
       outside main channels, primarily along the banks). Reef should be located at an
       appropriate depth. Although oysters recruited in both intertidal and subtidal depths to
       <1.5 m deep, the greatest total number of oysters were found in the intertidal zone
       approximately 0.1-0.2 m above the Low Tide Mark.
      Timing the deployment of pilot reefs to coincide with period of maximum recruitment
       potential (late summer to autumn based on the results if this study).
      A range of surface materials including concrete and recycled plastic could be suitable
       for use as initial settlement structures.
      We expect that establishment of a few trial reefs to cost in the order of $50-100K,
       including detailed monitoring.
      We also suggest that settlement monitoring is continued in concert with this pilot reef
       program. This will provide information about inter-annual variation in recruitment, and
       hopefully the reasons why Sydney rock oysters do or do not recruit successfully in
       different years. We also recommend that a key variable tested in the next iteration of
       settlement monitoring is settlement onto oyster shells.
      Hatchery oyster stock may be needed to boost larval supply but this should not be
       considered until at least another season of studying natural recruitment, because
       involving a hatchery increases the costs and complexity of restoration projects.