11

Outer Harbour

AREA 176.97 km2
 Overall Result

Situated in open coastal waters between Facing Island and Rodds Bay, the Outer Harbour is the largest of the 13 monitoring zones. Just over 50% of this zone lies within the Gladstone Port Limits. The south-western boundary consists of long sandy beaches and salt pans and mangroves around the entrance to Colosseum Inlet. There are no major industries located along the coastlines of this zone. Coral reefs occur within the zone and there are two coral monitoring sites. The north-eastern boundary consists of open coastal water and a dredge spoil ground is located to the east of this boundary.

This zone has three water and sediment monitoring sites, two coral monitoring sites 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
Outer Harbour received an overall water quality score of 0.97 (A). This score was based on the scores for physicochemical (1.00), nutrients (0.91) and dissolved metals (1.00).

Sediment quality
Sediment quality of the Outer Harbour was very good with an overall score of 0.98 (A).


Measures Results

Water
Sediment

The Outer 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 Outer Harbour received a very good overall score for nutrients (0.91). Total phosphorus (1.00) and chlorophyll-a (0.99) has very good scores and total nitrogen had a good score (0.74), 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

Corals Results

The 2021 Gladstone Harbour Report Card scores for the Outer Harbour zone are based on data collected from two reefs: Seal Rocks North and Seal Rocks South.

The overall score for coral health in the Outer Harbour was 0.12 indicating a very poor condition. This score was a slight decrease from the previous year (0.14).

Coral cover scores were very poor at both Seal Rocks North (0.01) and Seal Rocks South (0.12). Similarly, the two reefs had identical very poor scores for macroalgae cover of 0.00. Both low coral cover and high macroalgal cover has been evidenced since 2015.

Both Seal Rocks North (0.10) and Seal Rocks South (0.20) received very poor scores for juvenile density indicating a low potential for coral recruitment at these reefs. Juvenile density scores have declined substantially at both reefs since 2018.

Hard coral cover change in the Outer Harbour remained poor (0.26), showing a decline compared to the 2020 score (0.39). 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 all mangrove condition for the Outer Harbour was 0.66 (B) indicating a good condition. Mangrove extent (0.76) was good and both canopy condition (0.64) and shoreline condition (0.59) were satisfactory.

The overall score in the Outer Harbour was similar to the score recorded in the previous year indicating little change in this zone.

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
11. Outer Harbour ND