ENVIRONMENTAL
RESULTS
AREA: 9.45 km2
ABOUT THE ZONE
South Trees Inlet is a mangrove and salt pan-lined tidal inlet that flows into the Mid Harbour Zone. The zone contains one monitored seagrass meadow which sits just off the northern tip of South Trees Island. At 10.9ha it is the second smallest of the monitored meadows. The area contains a large number of industrial developments, including South Trees Wharf on South Trees Island at the inlet’s mouth, Queensland Alumina Ltd to the west of the inlet, and Boyne Smelters to the south-west of the inlet. The South Trees Industrial Estate is located next to Wapentake Creek which flows into the western side of the inlet just south of South Trees Island.
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This zone has six water and sediment monitoring sites, three monitored seagrass meadows, three fish monitoring sites and one mangrove monitoring sub-zone.
WATER & SEDIMENT
WATER
SEDIMENT
South Trees Inlet received an overall water quality score of 0.79 (B). This score was based on the scores for physicochemical (0.81), nutrients (0.57) and dissolved metals (1.00).
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Sediment quality of South Trees Inlet was very good with an overall score of 0.97 (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
South Trees Inlet 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 satisfactory score for turbidity (0.61) indicating that average turbidity was below the guideline value.
All six dissolved metals received very good scores (0.98-1.00) indicating that average concentrations were well below the water quality guideline values.
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South Trees Inlet received a satisfactory overall score for nutrients (0.57). Total phosphorus had a good score (0.77) while total nitrogen had a satisfactory score (0.53), indicating that average concentrations for these measures were below the guideline values for this zone. In contrast, chlorophyll-a had a poor score (0.41) as the average concentration was above the guideline value.
HABITATS
SEAGRASS (MEADOW 60)
This zone has one monitored meadow which sits off the northern tip of South Trees Island. Meadow 60 is an intertidal meadow and the second smallest of the monitored meadows.
The overall condition of this meadow remains very good (1.00, A), with all three sub-indicators in very good condition for the fifth consecutive year. This marks the sixth year of improved seagrass condition from the overall poor condition (0.48, D) in 2016. Both meadow biomass and area received the highest possible scores (1.00, A) with species composition also receiving a very good score (0.99, A).
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 score was 0.60 indicating a satisfactory condition for mangroves. Canopy condition (0.50) and shoreline condition (0.51) were satisfactory. Mangrove extent (0.79) received a good score, a result of a net gain in relative mangrove area. However, it is important to note that the health of mangroves is being measured from a 2013-14 baseline and considerable clearing and habitat modification has occurred in these areas in the past.
FISH & CRABS
FISH HEALTH RESULTS
HARBOUR SCORE
OVERALL VISUAL FISH CONDITION: HARBOUR SCORE
VISUAL FISH CONDITION: HARBOUR SCORE
FISH HEALTH ASSESSMENT INDEX: HARBOUR SCORE
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
Fish Health (Overall)
The overall score calculated for fish health in 2022 was 0.80 (B), which is an average of the scores for Fish Condition 0.72 (B) and the Health Assessment Index 0.90 (A).
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Visual Fish Condition:
The overall score for Fish Condition (0.72) is an average of 0.97 (A) for Fish Visual Condition (FVC) and 0.47 (D) for Fish Body Condition (FBC).
The high scores for FVC are a result of a low incidence of poor visual health. All fish species assessed for this metric received very good scores ranging from 0.90 (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 poor score for FBC in 2022 was a result of poor scores for yellow-finned bream (0.43), pikey bream (0.46) dusky flathead (0.43), and barred javelin (0.44). Almost all species assessed had a mean body condition below the long-term average (2003 – 2021). However, the remaining species assessed, mangrove jack, had a satisfactory score of 0.50.
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Fish Health Assessment Index (HAI):
The overall HAI score for Gladstone Harbour was 0.90 (A), as data from the 2021 Gladstone Harbour Report Card was reused.
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 Fish Visual 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 2022 was 0.57 (C) similar to the 2020 score of 0.62. The final scores were measured against a 2012 to 2021 baseline. The 2022 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 2022 reporting year was 764, 316 yellow-finned bream and 448 pikey bream.