5

Inner Harbour

AREA 33.68 km2
 Overall Result

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. Coral reefs have been recorded at Turtle, Quoin and Diamantina islands although there is little evidence that these areas have recently supported viable coral communities. There are several seagrass meadows, including one monitored seagrass meadow in the north of this zone. The Quoin Island Turtle Rehabilitation Centre is located in the centre of this zone and the Barney Point Coal Terminal is located on the south-east banks of the zone.

This zone has three water and sediment monitoring sites, one seagrass monitoring meadow, two fish monitoring sites, one mud crab monitoring site and two 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 Inner Harbour received an overall water quality score of 0.94 (A). This score was based on the scores for physicochemical (1.00), nutrients (0.82) and dissolved metals (1.00).

Sediment quality
Sediment quality of the Inner Harbour was very good with an overall score of 0.94 (A).


Measures Results

Water
Sediment

The Inner 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 very good score for turbidity (1.00) indicating that average turbidity was well 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.

The Inner Harbour received a good overall score for nutrients (0.82). Total phosphorus had a very good score (1.00) and total nitrogen (0.75) and chlorophyll-a (0.71) 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
58 0.59 0.91 0.60 0.59 0.59

The Inner Harbour has one monitored, intertidal meadow in the south-east corner of the zone near South Trees Inlet.

The Inner Harbour was in satisfactory condition (0.59). This was a lower condition score than in 2020 when Meadow 58 was in good condition. The decrease in score was driven by lower biomass and species composition scores than the previous year. In 2021 both biomass and species composition scores were satisfactory, 0.59 and 0.60 respectively. Although meadow area was also lower than in 2020 it still received a very good score (0.91) for the second consecutive year.

Mangrove Results

The overall mangrove score for the Inner Harbour was 0.55 (C) indicating a satisfactory condition for mangroves in this zone. Mangrove extent (0.62), canopy condition (0.51) and shoreline condition (0.52) were all satisfactory.

The overall score improved from 0.43 in 2018 to 0.55 in 2019. This was one of three zones where an improved overall score was recorded.

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
5. Inner Harbour 0.61

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.

Mud Crabs Results

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.

The overall zone score for the Inner Harbour was 0.39 indicating a poor condition for mud crabs—an identical result to 2020 (0.39). Scores for the sub-indicators were mixed. Abundance received a satisfactory score (0.63), sex ratio received a very poor score (0.07) and prevalence of rust lesions was poor (0.47). The prevalence of rust lesions score was the lowest zone score for this sub-indicator.