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
WATER
SEDIMENT
Graham Creek received an overall water quality score of 0.92 (A). This score was based on the scores for physicochemical (1.00), nutrients (0.76) and dissolved metals (1.00).
Sediment quality of Graham Creek was very good with an overall score of 0.95 (A).
MEASURES RESULTS
WATER
SEDIMENT
pH = acidity TN = Total nitrogen TP = Total phosphorus Chl-a = Chlorophyll-a Al = Aluminum Cu = Copper Pb = Lead Mn = Magnesium Ni = Nickel Zn = Zinc
As = Arsenic Cd = Cadmium Cu = Copper Hg = Mercury Pb = Lead Ni = Nickel Zn = Zinc
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
Graham Creek received a very good score of 1.00 for pH indicating that the average pH was well within the guideline value range. This zone received a very good score for turbidity (0.96) indicating that average turbidity was well below the guideline value.
All six dissolved metals received very good scores (1.00) indicating that average concentrations were well below the water quality guideline values.
Graham Creek received a good overall score for nutrients (0.76). All three sub-indicators had satisfactory or above scores, indicating that average concentrations for all three measures were below the guideline values for this zone. Total phosphorus had a very good score (0.85), total nitrogen had a satisfactory score (0.59), and chlorophyll-a had a good score (0.68).
HABITATS
MANGROVE RESULTS
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
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 HEALTH RESULTS
HARBOUR SCORE
VISUAL FISH CONDITION: HARBOUR SCORE
FISH HEALTH ASSESSMENT INDEX: HARBOUR SCORE
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
Fish Health (Overall)
The overall score calculated for fish health in 2021 was 0.82 (B), which is an average of the scores for Visual Fish Condition 0.74 (B) and the Health Assessment Index 0.90 (A).
Visual Fish Condition:
The overall score for the visual fish condition is an average of 0.97 (A) for Fish Visual Assessment (FVA) and 0.50 (C) for Fish Body Condition (FBC).
The high scores for FVA are a result of a low incidence of poor visual health. All fish species assessed for this metric received very good scores ranging from 0.94 (A) to 0.98 (A). This result was similar to the HAI scores for external measures where a very low number of external health issues were recorded.
The satisfactory score for FBC in 2021 was a result of poor scores for yellow-finned bream (0.47) and pikey bream (0.48). Both species assessed had a mean body condition below the long-term average (2003 – 2020). However, the remaining three species assessed all had satisfactory scores ranging from 0.54 to 0.55.
Fish Health Assessment Index (HAI):
The overall HAI score for Gladstone Harbour was 0.90 (A).
This was comprised of scores from five fish species, barramundi 0.98 (A), barred javelin 0.90 (A) and blue catfish 0.81 (B), bream 0.98 (A) and mullet 0.81 (B).
In general, the surveyed fish species showed very few signs of external health issues, a similar result to the Visual Fish Condition sub-indicator. Scores for internal organs were also low indicating good to very good fish health.
FISH RECRUITMENT RESULTS
Fish recruitment was assessed for two species: yellow-finned bream Acanthopagrus australis and pikey bream Acanthopagrus pacificus. The overall score for 2021 was 0.62 (C) similar to the 2020 score of 0.64. The final scores were measured against a 2012 to 2020 baseline. The 2021 score for fish recruitment indicates a season with higher recruitment rate (increased catch rate) relative to the mean reference level determined over the baseline period. The total number of bream caught in the 2021 reporting year was 626, 329 yellow-finned bream and 297 pikey bream. Pikey bream tended to dominate in the northern sites while yellow-finned bream tended to dominate in the southern sites.
MUD CRAB RESULTS
Graham Creek is a mangrove-lined tidal inlet located near the south-west corner of Curtis Island. It is approximately 9 km long and flows into the southern end of The Narrows.
The overall zone score for Graham Creek was 0.39 indicating a poor condition for mud crabs. Since 2018, Graham Creek has consistently received a very poor score (0.34–0.45). In 2021, abundance was poor (0.27) while sex ratio was very poor (0.00). The very good score for prevalence of rust lesions (0.89) indicated a very low incidence of this condition at Grahams Creek.