ENVIRONMENTAL
.RESULTS
ABOUT THE ZONE
The Narrows is lined by mangroves and saltmarsh, provides sheltered water for mud crabs and is an important area for recreational and commercial mud crab fishers.
WATER & SEDIMENT
The Narrows received an overall water quality score of 0.75 (B).
Sediment quality of The Narrows was very good with an overall score of 0.91 (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 The Narrows scored 0.75 and received a Good (B) grade, similar 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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The Narrows received a Very Good (A) grade for pH (1.00), and Satisfactory (C) grades for turbidity (0.54), total nitrogen (0.51) and total phosphorus (0.55). All of the six dissolved metals received a Very Good (A) grade. This indicates that average concentrations for these measures were within the guideline values for this zone. Chlorophyll-a received a Poor (D) grade and a score of 0.42.
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For Sediment quality, The Narrows received an overall score of 0.91 and a Very Good grade (A), retaining the same result as 2024. 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 (0.76) and nickel (0.65) received a Good (B) grade. Both are naturally occurring within the harbour and may not be associated with anthropogenic inputs.
HABITATS
SEAGRASS (MEADOW 21)
The Narrows features one long-term monitoring meadow at Black Swan Island, an intertidal area with variable biomass. Since inclusion in the Gladstone Harbour Report Card in 2015, the condition of this meadow has steadily improved, consistently receiving a Very Good (A) grade for the past four years. 2025 marks the longest consecutive period of high scores for any meadow.
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 The Narrows declined from Good (B) in 2019 to Satisfactory (C).
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The mangrove extent sub-indicator, which measures changes in canopy cover relative to saltmarsh and saltpan areas, retained a Good (B) grade. The canopy condition indicator, based on remote sensing of canopy density and health, improved from Satisfactory (C) to Good (B). However, shoreline condition, assessed through aerial surveys of mangroves bordering Gladstone Harbour’s water quality zones, declined to Poor (D) in 2024.
FISH & CRABS
FISH RESULTS
Fish recruitment was assessed for two species: Yellowfin bream Acanthopagrus australis and Pikey bream A. pacificus. The overall score for 2025 was higher than the previous year (2024: 0.44, 2025; 0.61) and improved from a Poor (D) to a Satisfactory (C). This is a result of increased catch numbers of both Yellowfin (2024: 35, 2025: 52) and Pikey (2024: 36, 2025: 63) bream.
MUD CRAB RESULTS
The overall zone score for Mud crabs for The Narrows was 0.87 and graded Very Good (A), an increase in both score and grade from 2024 (0.65, Good, B). At the sub-indicator level, abundance declined from a Very Good (A) to a Good (B) grade, reflecting a lower catch 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 Narrows improved from a Very Poor (E) 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 indicating a very low number of crabs with rust lesions.