ENVIRONMENTAL
RESULTS
AREA: 0.75 km2
ABOUT THE ZONE
Boat Creek is a small mangrove-lined estuary connected to the western side of the Western Basin. This long (approximately 9km), narrow water body is not well flushed during regular tides. It is a small zone that only includes approximately 2km of waterway and a small open harbour area near the mouth.
This zone has three water and sediment monitoring sites, one fish monitoring sites, a mud crab monitoring site and one mangrove monitoring sub-zone.
WATER & SEDIMENT
Boat Creek received an overall water quality score of 0.69 (B).
Sediment quality of Boat Creek was very good with an overall score of 0.94 (A).
The following graphs compare the Water and Sediment scores reported for 2023 (top line) to those from the previous year.
WATER
SEDIMENT
Very good (0.85-1.00)
Poor (0.25-0.49)
Good (0.65-0.84)
Satisfactory (0.5-0.64)
Very Poor (0.00-0.24)
No data available
Overall, Water quality in Boat Creek scored 0.69 and received a good grade (B), similar to the 2022 report card. This score was calculated by aggregating the three sub-indicator and associated measure scores (Physiochemical – pH and turbidity, Nutrients – total nitrogen, total phosphorus and dissolved metals, and dissolved metals – aluminum, copper, lead, manganese, nickel and zinc).
Within the Physiochemical sub-indicator, Boat Creek received a score of 1.00 and a very good grade (A) for pH indicating that the average pH was well below the guideline value range. This zone received a score of 0.36 and poor grade (D) for turbidity indicating that average turbidity was above the guideline value.
Within the Nutrient sub-indicator group, total nitrogen (0.28) received a poor grade (D) and total phosphorus (0.20) a very poor grade (E), indicating these measures were above the guideline values, while chlorophyll-a (0.67) received a good grade (B), indicating that average concentrations for chlorophyll-a were below the guideline values for this zone.
All six Dissolved metals received high scores (1.00) and very good grades (A) indicating that average concentrations were well below the water quality guideline values.
For Sediment quality, Boat Creek received an overall score of 0.94 and a very good grade (A), also a similar result to the previous year. This score was calculated by aggregating one sub-indicator and associated measure scores (Metal and metalloids – arsenic, cadmium, copper, lead, mercury, nickel and zinc).
In 2023, six of the seven Metal and metalloid sub-indicator measures received very high scores (0.89–1.00) and very good grades (A), while one measure – nickel – received a score of 0.70 and a good grade (B). These results reflect that all concentrations were below the guideline values for this zone.
HABITATS
MANGROVE RESULTS
No Mangrove assessment was conducted in 2023, results are from monitoring conducted in 2019. The overall zone score for Boat Creek was 0.46 (D) indicating a poor condition. Mangrove extent (0.54) was satisfactory and canopy condition (0.38) and shoreline condition (0.46) were poor.
The overall score for Boat Creek fell from 0.63 in 2018 to 0.46 in 2019. This was largely a result of changes in canopy condition where the score declined from 0.61 in 2018 to 0.38 and a decline in shoreline condition from 0.63 to 0.46 in 2019. This may reflect the impacts off decreased rainfall over the reporting year and increased shoreline erosion.
FISH & CRABS
FISH RECRUITMENT RESULTS
The Fish indicator is comprised of two sub-indicators, Fish Health and Fish Recruitment.
Fish recruitment was assessed for two species: Yellowfin bream Acanthopagrus australis and Pikey bream Acanthopagrus pacificus. The overall score for 2023 was higher than the previous year (2022: 0.33, 2023: 0.58 and improved one grade to satisfactory (C). This increase in score is a result of an increase in number of bream caught during the 2022-23 reporting period (2022 report card: 1 fish, 2023 report card: 5 fish).
Fish health is assessed though two sub-indicators, Fish condition and Fish Health Assessment Index (HAI).
The overall score for Fish health in 2023 was 0.81 and received a good grade (B). The 2023 results were calculated by the average of the Fish HAI score (0.90; results carried over from 2021) and new assessment of Fish condition which scored similar to the previous year (2022: 0.74, 2023: 0.73).
MUD CRAB RESULTS
The overall zone score for Boat Creek increased from the previous year and resulted in an improved grade from satisfactory (C) to good (B). This increase was largely due to an improvement in the sex ratio score, a reflection of more males being caught than females. In contrast, abundance remained low (low scores), and prevalence of rust lesions remained low (high scores).