2020-07-07 P&E Agenda - Item 3 - Attachment 1 - TNC Project Management Plan

Measuring shellfish survivorship and growth (Shellfish metrics)

Shellfish restoration, in this project, primarily relies on the natural recruitment of rock oyster
spat onto the restoration substrate. Scientists have determined that the Noosa River estuary
is primarily ‘substrate limited’, meaning there is insufficient substrate, of suitable
configurations and locations, in the estuary, on which can settle, bind together and form self-sustaining shellfish
ecosystems.
Fortunately, surveys indicate that there in sufficient numbers of rock oysters growing individually, or in small
clusters, in the estuary to provide oyster ‘spat’, or juvenile oysters, to colonise the restoration substrates deployed
by the project.
Relying exclusively on natural oyster spat recruitment, and growth, on the restoration substrate, however, would
be risky. Rock oysters face many recruitment limitations in the estuary. Rock oysters spawn seasonally, and the
quantity of spat released into the estuary can vary significantly between seasons. High suspended sediment loads
in the estuary readily smother juvenile oysters, causing high mortalities of settled individuals.
Other oyster and non-oyster species, including pearl oysters, hairy mussels and fast-growing macroalgae, readily
settle on the same substrates as rock oysters, thus providing direct competition for colonization space. These
other rapid colonizers do not in themselves create the vertical relief, and habitat complexity, that rock oysters
provide.
Pathogens, which infest and kill oysters are also ever present in the estuary sediments, and a multitude of
vertebrates and invertebrates, from stingrays to finfish, shorebirds to gastropods, predate directly on oysters.
These limitations have collectively prevented the natural restoration of shellfish ecosystems in the Noosa River
estuary to date, so restoration efforts must augment the natural recruitment and growth of oysters and
associated species.
In response, it is often necessary for the project to seed the restoration sites with live adult and/or juvenile
oysters. Juvenile oysters may be settled onto shell in a hatchery. Adult oysters may be translocated from oyster
growing areas, as individual oysters or ‘clumps’, and set on the restoration substrate using direct hand-setting or
vessel deployment techniques.
Method: Hatchery-produced juvenile oysters
For hatchery-produced live oysters, destined for restoration deployment, an initial average density of juvenile
oysters (spat) is calculated by the hatchery by counting how many spat have settled onto 50 individual shell ‘culch’
(dried, sterile oyster shell put in a tank for the purpose of spat settlement). This count gives an estimated total
number of total individual juveniles will be deployed onto the restoration substrate from the hatchery-cultured
oyster batch. These estimates of ‘live spat on shell’, are provided pre-deployment to monitor the impact of
translocation on oyster survivorship.
Method: Translocation of adult oysters
Where aquaculture-produced rock oysters have been grown out to adult size, these may be available locally, from
hatcheries or oyster farms. These need to be collect, in a timely manner, housed in suitable transport containers
and translocated to the restoration site in a timely way to minimize stress and mortality. Individual oysters, and
even clumps of oysters may be scattered onto the restoration substrate from a vessel, or laid, by hand, by
suitability qualified divers, or through placing the oysters onto the substrate, again by hand, at low tide.
At the time of collection, a sample of oysters are counted, or weighted, and the total number, or weight of the
oysters, to be used in the restoration effort determined. This counting allows for survivorship post deployment
to be measured and reported. The precise locations where adult oysters are set on each site may be determined
using GPS coordinates and digital mapping software.
Method: Survivability and Growth - In-water sampling
Shellfish are collected by sampling two transects per site with five quadrats (0.25 m2) on each side of the transect
line (i.e. 10 quadrats per transect).




77 | Bring Back the Fish MER plan 2020 – 2022