ENVIRONMENTAL
RESULTS
AREA: 176.97 km2
ABOUT THE ZONE
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.
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This zone has three water and sediment monitoring sites, two coral monitoring sites and two mangrove monitoring sub-zones.
WATER & SEDIMENT
The Outer Harbour received an overall water quality score of 0.94 (A).
Sediment quality of the Outer Harbour was very good with an overall score of 0.99 (A).
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The following graphs compare the Water and Sediment scores reported for 2023 (top line) to those from the previous year.
WATER
SEDIMENT
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
Overall, Water quality in the Outer Harbour (0.94) scored slightly higher than the 2022 report card, however, the overall grade (very good, A) remained unchanged. This score was calculated by aggregating the three sub-indicator and associated measure scores (Physiochemical – pH and turbidity, Nutrients – total nitrogen, total phosphorus and dissolved metals, and dissolved metals – aluminum, copper, lead, manganese, nickel and zinc).
Within the Physiochemical sub-indicator, Outer Harbour received very good grades (A) for both pH (1.00) and turbidity (0.97) indicating that both measures were well below the guideline values.
Within the Nutrient sub-indicator group, total nitrogen (0.69) and chlorophyll-a (0.82) received good grades (B) indicating concentrations for these measures were below guideline values. Total phosphorus (1.00) received a very good grade (A), indicating that average concentrations for this measure was well below the guideline value.
All six Dissolved metals received high scores (1.00) and very good grades (A) indicating that average concentrations were well below the water quality guideline values.
For Sediment quality, Outer Harbour received an overall score of 0.99 and a very good grade (A), also a similar result to the previous year. This score was calculated by aggregating one sub-indicator and associated measure scores (Metal and metalloids – arsenic, cadmium, copper, lead, mercury, nickel and zinc).
In 2023, all seven Metal and metalloid sub-indicator measures received very high scores (0.96–1.00) and very good grades (A), indicating that average concentrations were well below the guideline values for this zone.
HABITATS
CORAL RESULTS
The 2023 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 in the Outer Harbour was 0.14 and graded very poor (E), indicating a very poor condition. The Outer Harbour Coral score slightly decrease from the previous year (2022: 0.18)
Compared to the previous year, coral cover scores decreased at both Outer Harbour reefs. Minor score variations have been observed over the past six years; however, these scores are still substantially lower than the 40% threshold required to receive a satisfactory grade (C) with both harbour zones were graded very poor (E) for coral cover.
Scuba surveys indicated that the bio-eroding sponge Cliona orientalis continues to impact the coral community across the whole harbour and in particular, colonies of Turbinaria at Seal Rocks South. Sponge prevalence is likely contributing to a lack of coral cover recovery across the harbour.
All reefs scored a very poor grade (E) for the eight consecutive year for Macroalgae cover. Community composition at the two Outer Harbour reefs was stable, with communities consistently dominated by the two brown macroalgae genera, Sargassum and Lobophora.
All reefs decreased scores and remained with very poor grades (E) for juvenile density. High coral cover in 2009 was linked to abundant representation of fast-growing, branching corals Acropora juveniles; however, in 2023, this juvenile family was notably lacking across the harbour. Recovery of corals may be limited until this family appears and survives.
Changes in hard coral cover has been graded poor (D) in the Outer Harbour reefs for the past six years. In general, the ongoing low scores and very poor grades demonstrates recovery of coral communities continues to fall short of modelled expectations.
MANGROVE RESULTS
No mangrove assessment was conducted in 2023, results are from monitoring ocnducted in 2019. 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.
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The overall score in the Outer Harbour was similar to the score recorded in the previous year indicating little change in this zone.
FISH & CRABS
HARBOUR SCORE
Fish Health (Overall)
The Gladstone Harbour 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).
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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).
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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.
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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.
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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).
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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.