8

Mid Harbour

AREA 95.73 km2
 Overall Result

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

Grading system
A
Very good (0.85-1.00)
B
Good (0.65-0.84)
C
Satisfactory (0.50-0.64)
D
Poor (0.25-0.49)
E
Very poor (0.00-0.24)
 
Data not available

Water & Sediment Quality Results

Water
Sediment

Water quality
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
Sediment quality of the Mid Harbour was very good with an overall score of 0.96 (A).


Measures Results

Water
Sediment

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

Grading system
A
Very good (0.85-1.00)
B
Good (0.65-0.84)
C
Satisfactory (0.50-0.64)
D
Poor (0.25-0.49)
E
Very poor (0.00-0.24)
 
Data not available

Seagrass Results

Meadow ID Biomass Area Species Composition Overall Meadow Score Overall Zone Score
43 0.33 0.87 0.50 0.33 0.48
48 0.64 0.72 0.97 0.64 0.48

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 remained poor (0.48) for the second consecutive year.

The overall poor condition was largely driven by Pelican Banks, which received a poor score (0.33) for the sixth consecutive year. While seagrass area remained very good and has improved markedly since 2017, biomass has remained poor or very poor since 2016. Species composition at Pelican Banks was satisfactory but has shown a similar declining trend as biomass.

In contrast, Meadow 48 was in satisfactory condition (0.64), showing satisfactory biomass, good area, and very good species composition scores. This was the first time since 2011 that this meadow was composed of the dominant species H. uninervis.

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

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 and Crabs

Grading system
A
Very good (0.85-1.00)
B
Good (0.65-0.84)
C
Satisfactory (0.50-0.64)
D
Poor (0.25-0.49)
E
Very poor (0.00-0.24)
 
Data not available

Fish Health Results

Harbour Score
Visual fish condition (VFC) 0.74
Fish health assessment index (HAI) 0.90

Visual Fish Condition: Harbour Score
FVA - Fish Visual Assessment
FBC - Fish Body Condition
Fish Health Assessment Index: Harbour Score
HAI - Health Assessment Index

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:

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

Zone ID Score
8. Mid Harbour 0.78

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.