ENVIRONMENTAL
RESULTS
AREA: 95.73 km2
ABOUT THE ZONE
The Mid Harbour zone is the second largest of the harbour zones, and is bounded by Facing, Curtis and Boyne Islands. Most shipping enters the harbour along the Gatcombe channels in the southern end of this zone. This zone contains two monitored seagrass meadows, including the largest seagrass meadow in the harbour at Pelican Banks. Within the zone, coral reefs occur along the western side of Facing Island and on the south-east tip of Curtis Island. The northern boundary of this zone also marks the boundary of the Great Barrier Reef Marine Park.
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This zone has six water and sediment monitoring sites, two monitored seagrass meadows, four coral monitoring sites, two fish monitoring sites and three mangrove monitoring sub-zones.
WATER & SEDIMENT
WATER
SEDIMENT
The Mid Harbour received an overall water quality score of 0.84 (B). This score was based on the scores for physicochemical (0.81), nutrients (0.69) and dissolved metals (1.00).
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Sediment quality of the Mid Harbour was very good with an overall score of 0.98 (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
The Mid Harbour 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 (0.62) indicating that average turbidity was 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.
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The Mid Harbour received a good overall score for nutrients (0.69). Total phosphorus had a very good score (0.89) while total nitrogen (0.56) and chlorophyll-a (0.64) had satisfactory scores, indicating that average concentrations for these measures were below the guideline values for this zone.
HABITATS
SEAGRASS RESULTS
Mid Harbour has two monitored meadows adjacent to the south-east corner of Curtis Island. Meadow 43, known locally as Pelican Banks, is the largest and most productive seagrass meadow assessed in the Gladstone Harbour Report Card. Pelican Banks is an intertidal meadow while Meadow 48 is a subtidal meadow neighbouring the eastern side of Quoin Island.
Overall condition of the Mid Harbour seagrass was good (0.67, B) for the first time since GHHP monitoring began in 2015. This was driven by improvements in both meadows.
Meadow 48 received a good score (0.80, B) for the first time since 2008. The change was driven by a marked improvement in biomass from the previous year, with area showing a slight improvement and species composition remaining very good.
Pelican Banks also showed an improved condition compared to previous years, receiving an overall satisfactory score (0.54, C) after six years of poor or very poor condition. This positive result was driven by notable improvements in both biomass and species composition as compared to the previous year.
CORALS RESULTS
The overall score for corals in the Mid Harbour was 0.13 indicating a very poor condition. This score was a decrease from the previous year (0.16).
All four reefs in this zone received very poor scores for coral cover ranging from 0.02 at Manning Reef to 0.13 at Rat Island. Macroalgae cover also received very poor scores at three reefs (0.00) and a poor score at Farmers Reef (0.29), indicating very high levels of macroalgae.
Juvenile density was very poor at Facing Island (0.06), Manning Reef (0.10) and Rat Island (0.07) and poor at Farmers Reef (0.27). This was the same pattern as in 2021. At the zone level, the juvenile density score has declined substantially since 2018.
Hard coral cover change in the Mid Harbour remained poor (0.26), declining from the 2021 score (0.43). The continued poor score indicating that the rate of increasing coral cover in this zone was lower than that observed at other nearshore reefs in the Great Barrier Reef.
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 the Mid Harbour was 0.55 (C) indicating a satisfactory condition for mangroves in this zone. This was a result of a poor score for mangrove extent (0.39), and satisfactory scores for canopy condition (0.63) and shoreline condition (0.63).
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This overall score for 2019 was identical to the score recorded in 2018.
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.
MUD CRAB RESULTS
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.
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The overall zone score for The Narrows was 0.64 indicating a satisfactory condition for mud crabs. This score was relatively comparable to the score from the previous four years (0.60–0.66). Sub-indicator patterns were mostly stable as abundance received a very good score (1.00) and sex ratio received a very poor score (0.00). The score for prevalence of rust lesions (0.92) was very good. While higher than in 2020, the prevalence of rust lesions score was comparable to those received from 2017 (0.90–1.00).