ENVIRONMENTAL
.RESULTS
AREA: 5.8 km2
ABOUT THE ZONE
Graham Creek is a mangrove-lined tidal inlet located near the south-west corner of Curtis Island. It is approximately 9km long and flows into the southern end of The Narrows. It is considered to be one of the best fishing spots in Gladstone Harbour. Three major creeks, Rawbelle, Hobble Gully and Logbridge, flow into Graham Creek. This is a relatively pristine zone that has significant biodiversity value and lies within the Great Barrier Reef World Heritage Area.
This zone has two water and sediment monitoring sites, two fish monitoring sites, one mud crab monitoring site and one mangrove monitoring sub-zone.
WATER & SEDIMENT
Graham Creek received an overall water quality score of 0.85 (A).
Sediment quality of Graham Creek was very good with an overall score of 1.00 (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)
Good (0.65-0.84)
Satisfactory (0.5-0.64)
Poor (0.25-0.49)
Very Poor (0.00-0.24)
No data available
Overall, Water quality in Graham Creek scored 0.85 and received a very good grade (A), 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, Graham 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. This zone received a score of 0.83 and a good grade (B) for turbidity indicating that average turbidity was below the guideline value.
Within the Nutrient sub-indicator, total nitrogen (0.64) had a satisfactory grade (C) and total phosphorus (0.84), a good grade (B), indicating that average concentrations for these measures were below the guideline values for this zone. In contrast, chlorophyll-a had a lower score (0.46) and a poor grade (D) as the average concentration were above the guideline value.
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, Graham Creek received an overall score of 1.00 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, all seven Metal and metalloid sub-indicator measures received very high scores (1.00) and very good grades (A), indicating that average concentrations were below the guideline values for this zone.
HABITATS
MANGROVE RESULTS
No mangrove assessment was conducted in 2023, the above results are from monitoring conducted in 2019. The overall zone score for Graham Creek was 0.64 (C) indicating a satisfactory condition for mangroves in this zone. Both mangrove extent (0.83) and shoreline condition (0.76) received good scores. However, canopy condition (0.34) was poor.
The overall score from Graham Creek declined from 0.67 in 2018 to 0.64 in 2019. This deterioration is attributed to a decline in canopy condition which may reflect the impacts off decreased rainfall over the reporting year.
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 lower than the previous year (2022: 0.80, 2023: 0.53) and declined one grade to satisfactory (C). This decline in score is a result of a decrease in number of bream caught during the 2022–23 reporting period (2022 report card: 107 fish, 2023 report card: 56 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 score for Graham Creek indicates a poor condition for Mud crabs in this zone. Since 2018, Graham Creek has consistently received a poor grade (D). Abundance and sex ratio scores remained very low, similar to the previous year, indicating low catch rates and poor balance between male and female crabs. In contrast, a very high score (1.00) for prevalence of rust lesions indicates a very low incidence of this condition at Graham Creek.