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.
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 0.91 (A). This score was based on the scores for physicochemical (0.92), nutrients (0.80) and dissolved metals (1.00).
Sediment quality of the Mid Harbour was very good with an overall score of 0.96 (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 good score for turbidity (0.84) 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.
The Mid Harbour received a good overall score for nutrients (0.80). Total phosphorus had a very good score (1.00) and total nitrogen (0.66) and chlorophyll-a (0.74) had good 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 declined from satisfactory to poor (0.43).
At Meadow 43, area was very good (0.95) while species composition was satisfactory (0.58). Biomass was the limiting sub-indicator, receiving a poor score (0.31) for the third consecutive year. Moreover, seagrass biomass at Pelican Banks has been below the baseline value since 2011.
At Meadow 48, area was very good (0.91) and biomass was good (0.75), with the former increasing and the latter decreasing when compared to 2019 scores. The overall score was driven by species composition, which received the lowest score (0.33) for the third consecutive year. The higher prevalence of smaller, colonising species (H. spinulosa and H. ovalis) of seagrass has resulted in a satisfactory or lesser condition at Meadow 48 since 2013.
CORALS RESULTS
The 2021 Gladstone Harbour Report Card scores for the Mid Harbour are based on data collected from four reefs: Facing Island, Farmers Reef, Manning Reef and Rat Island.
The overall score for corals in the Mid Harbour was 0.16 indicating a very poor condition. This score was a decrease from the previous year (0.20).
All four reefs in this zone received very poor scores for coral cover ranging from 0.02 at Manning Reef to 0.15 at Rat Island. Macroalgae cover also received very poor scores at all four reefs (0.00), indicating very high levels of macroalgae.
Juvenile density was very poor at Facing Island (0.02), Manning Reef (0.18) and Rat Island (0.10) and poor at Farmers Reef (0.30). At the zone level, the juvenile density score declined substantially since 2018.
Hard coral cover change in the Mid Harbour remained poor (0.43), showing a minor decline compared to the 2020 score (0.44). 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).
This overall score for 2019 was identical to the score recorded in 2018.
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.