ENVIRONMENTAL
RESULTS
ABOUT THE ZONE
The Inner Harbour is located immediately to the east of the Western Basin and is bounded by mangroves on Curtis Island and the town of Gladstone on the southern edge.
WATER & SEDIMENT
The Inner Harbour received an overall water quality score of 0.86 (A).
Sediment quality of the Inner Harbour was very good with an overall score of 0.95 (A).
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The following graphs compare the Water and Sediment scores reported for 2025 (top line) to those from 2024.
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 Inner Harbour scored 0.86 and received a Very Good (A) grade, an improvement to the 2024 Report Card. This score was calculated by aggregating the three sub-indicator and associated measure scores (Physicochemical – pH and turbidity, Nutrients – total nitrogen, total phosphorus and chlorophyll-a, and dissolved metals – aluminium, copper, lead, manganese, nickel and zinc).
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Inner Harbour received a Very Good (A) grade for pH (1.00), turbidity (0.87), and total phosphorus (0.94), and a Satisfactory (C) grade for total nitrogen (0.61). All of the six of the dissolved metals received a Very Good (A), indicating that average concentrations for these measures were within the guideline values for this zone. Chlorophyll-a received a score of 0.44, resulting in a Poor (D) grade.
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For Sediment quality, Inner Harbour received an overall score of 0.95 and a Very Good grade (A), 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). The results reflect that all concentrations were below the guideline values for this zone. Arsenic received a Good (B) grade. Arsenic is naturally occurring within the harbour and may not be associated with anthropogenic inputs.
HABITATS
SEAGRASS (MEADOW 58)
In the south-east corner of Inner Harbour, near South Trees Inlet, there is one long-term monitoring meadow. This meadow showed improvements in species composition score, rising from 0.00 to 0.49, and an improvement in overall meadow score (2024: 0.43, 2025: 0.62) compared to the previous year. Despite these gains, the overall condition of the meadow remains a Satisfactory (C) due to the continued dominance of the less persistent species Halophila ovalis.
MANGROVE RESULTS
The 2025 Gladstone Harbour Report Card incorporates the 2024 Mangroves results. Mangrove condition has historically remained stable due to strong buffering capacity, and since 2019, monitoring has been undertaken every five years. In 2024, the overall grade for Mangroves at Inner Harbour remained at a Satisfactory (C).
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The mangrove extent sub-indicator, which measures changes in canopy cover relative to saltmarsh and saltpan areas, declined from Satisfactory (C) to Poor (D). The canopy condition indicator, based on remote sensing of canopy density and health, remained at a Satisfactory (C) across years. Shoreline condition, assessed through aerial surveys of mangroves bordering Gladstone Harbour’s water quality zones, also remained stable, receiving a Satisfactory (C).
FISH & CRABS
FISH RECRUITMENT RESULTS
Fish recruitment was assessed for two species: Yellowfin bream Acanthopagrus australis and Pikey bream A. pacificus. Fish recruitment in the Inner Harbour remained at a Good (B) grade in 2025, with a similar score received across years (2024: 0.77, 2025: 0.75). The catch number of Yellowfin bream increased (2024: 4, 2025: 7), although Pikey bream (2024: 145, 2025: 130) declined.
MUD CRAB RESULTS
The overall zone score for Mud crabs for the Inner Harbour was 0.68 and graded Good (B), an increase to 2024 (0.45, Poor, D). At the sub-indicator level, abundance remained at a Very Poor (E) grade, reflecting a low catch per unit effort rate. Mud crab populations may be influenced by both human activities and natural factors, including habitat, reproductive cycles, and environmental conditions like temperature and water movement.
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In Queensland, it is illegal to take female crabs, hence changes in the ratio of male to female crabs can indicate changes in fishing pressures. Sex ratio for the Inner Harbour improved from a Very Poor (E) 2024 to a Very Good (A) grade in 2025, indicating a balance of males and females. The prevalence of rust lesions retained a Very Good (A) grade and indicates a very low number of crabs with rust lesions.