Description: Oyster reefs are complex, intertidal or subtidal living structures which are formed from clusters of living oysters and old shell. Oyster reefs are a distinct ecological community which provide a wide range of ecosystem services to coastal communities. Australia’s coastal environments have changed considerably since European arrival and it is estimated that 99% of our natural oyster reefs have been lost’. In NSW, small oyster populations still exist in most bays and estuaries but at very low densities compared to the pre-European period. MAPPING OYSTER REEFS IN NSW ESTUARIES Assessments on the global condition and abundance of oyster reefs in ecoregions have been widely published. However, little data exists at a local scale to guide regional or estuary-specific oyster reef restoration or contribute to other aspects of coastal management. To assist with this data gap, a key activity of the NSW Marine Estate Management Strategy's Oyster Reef Restoration Project is to identify and map current and historical reef sites. This information will be used to better understand the current state of oyster reef habitat in NSW. It will also assist in identifying areas that may need focused protection, provide research and monitoring sites and help plan for future restoration projects. The process developed for mapping historical oyster reefs in priority estuaries uses a multi-step identification and validation process including: 1) Desktop analysis of historical and local stakeholder information to identify likely locations of reefs; 2) Desktop analysis of satellite and aerial imagery to identify likely reefs ≥ 5m2; 3) Field validation of the digitised data and collection of additional reef characteristics; and 4) Desktop amendment following field assessments. INFORMATION FOR DESKTOP-BASED ANALYSIS Historical and local stakeholder information is used to target image analysis of possible oyster reef locations. Various imagery including Nearmap and aerial photography dated 2019 or more recent is used to digitise areas of visible inter-tidal oyster reef at a scale of 1:500-1:2000. Older imagery is used if recent imagery is not available. Where available a variety of image dates have been used to confirm the presence or extent of oyster reef. The following attributes are recorded prior to field validation: Estuary (estuary name); Region (south, central, northern); Source (image source and date); Scale (scale used when digitising); Verified (for completed field verification); Comments; Components of the field based mapping are completed during the desktop analysis where possible to assist with field verification. Following desktop analysis, field verification is undertaken and field based mapping definitions applied to the attributes (see below). Higher amounts of field verification are generally undertaken for estuaries with small amounts of oyster reef or where imagery is poor quality. Larger estuaries will generally have a smaller proportion of verification undertaken. DEFINITIONS FOR FIELD-BASED MAPPING NSW Department of Primary Industries (DPI) have developed the following criteria and definitions for capturing oyster reef characteristics in the field. These criteria are based on existing oyster reef definitions, modified classification systems used for other estuarine habitat mapping (e.g. descriptors for estuarine macrophyte mapping) and practical field-based testing of criteria appropriate for oyster populations in NSW estuaries. CRITERIA AND OPTIONS 1. REEF TYPE (only areas with at least 1 patch ≥ 5m2 in size is determined to be reef) (a) low profile (0.05 - 0.15m in height compared to surrounding substrate) (b) high profile (0.15 - 0.5m in height compared to surrounding substrate ) (c) clumping (small aggregations of oysters surrounded by sediment within a continuous area of oyster reef at least 5m2 in size ) (d) shell bed (traditional shell beds including historic cultivation type and middens) (e) oyster veneer (only 5cm or ≤ 2 layers thick) (f) combination (reefs which contain a combination of types e.g. a few high-profile beds and clumps and encrusted pneumatophores) (g) other 2. ESTUARY LOCATION (a) fringing (on foreshore) (band of reef along the foreshore edge, total area needs to ≥ 5m2 ) (b) independent (island) (reef patches surrounded by sediment/water channels ) (c) combination (if large area of reef extending well beyond the shoreline with mix of islands and fringing reef ) 3. PRIMARY OYSTER SETTLEMENT SUBSTRATE (a) legacy oyster farming structures (includes collapsed rack and rail and historic 'peg' rocks which were farmed ) (b) anthropogenic rock (includes ballast rock) (c) natural rock (includes bedrock and areas with cobble/large loose rock) (d) seawall (includes training walls ) (e) mangrove (includes thick aggregations on pneumatophores) (f) sediment (sand or mud) (g) unknown (possibly rock underneath but too difficult to determine ) 4. TIDAL PLANE (ELEVATION) (a) intertidal (if emerged at low tide ) (b) subtidal (if totally submerged at low tide) 5. REEF STRUCTURE/ DENSITY (a) continuous dense (single large bed or reef structure which is ≥ 5m2 with ≥ 60% oyster coverage) (b) continuous sparse (single large bed or reef structure which is ≥ 5m2 with < 60% oyster coverage) (c) patchy dense (series of reef patches interspersed with sand or rock, at least one of which is ≥ 5m2. Total coverage of patches within the reef ≥ 60% ) (d) patchy sparse (series of reef patches interspersed with sand or rock, at least one of which is ≥ 5m2. Total coverage of patches within the reef <60% ) 6. SPECIES (a) Sydney Rock Oyster (Saccostrea glomerata) (b) Pacific Oyster (Crassostrea gigas) (c) Angasi (Flat) Oyster (Ostrea angasi) (d) Leaf Oyster (Isognomon ephippium) (e) Cockles (Cardiidae (Katelysia scalarina, Anadara trapezius)) (f) Mussels e.g. Trichomya hirsute, Brachidontes rostratus, Xenostrobus pulex (g) other 7. STATUS OF SHELL IN REEF (a) live oyster (b) dead shell (c) other 8. TIDE (at time of data collection) (a) high tide (b) low tide (c) mid tide (d) non-tidal 9. FIELD SOURCE (a) stakeholder (b) DPI assessor (c) other DESKTOP AMENDMENT FOLLOWING FIELD VERIFICATION Following field verification, areas and attributes are checked for errors. An area attribute is added and calculated in square meters (Area_m2). Final checking is undertaken by the relevant Regional Manager in the Oyster Reef Restoration Project Team. For further information contact Joe Neilson Senior Manager, Marine Estate (Spatial Planner). Joe.Neilson@dpi.nsw.gov.au or Phone (02) 4222 8337.