ENVIRONMENTAL
RESULTS
AREA: 18.98 km2
ABOUT THE ZONE
Colosseum Inlet is an estuarine zone that is sheltered by Hummock Hill Island. Colosseum Inlet connects to both the Outer Harbour and Rodds Bay zones. It is outside the Gladstone Port Limits and inside the Great Barrier Reef World Heritage Area. The inlet has several large tributaries branching off the main creek and all are lined with mangroves and salt pan areas. There are no urban or industrial areas along the coastline of this zone. This is a relatively pristine zone that has significant biodiversity value.
This zone has four water and sediment monitoring sites, two fish monitoring sites and two mangrove monitoring sub-zones.
WATER & SEDIMENT
Colosseum Inlet received an overall water quality score of 0.88 (B).
Sediment quality of Colosseum Inlet was very good with an overall score of 0.96 (A).
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 Colosseum Inlet (0.88) scored slightly higher than the 2022 report card and resulted in an improvement to the overall grade (very good, A). 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, Colosseum Inlet received very good grades (A) for both pH (1.00) and turbidity (0.94) indicating that both measures were well below the guideline values.
Within the Nutrient sub-indicator both total nitrogen (0.56) and chlorophyll-a (0.62) had satisfactory grades (C), indicating that average concentrations for these measures were within the guideline values for this zone. In contrast, total phosphorus (0.80) received a good grade (B) as the average concentrations was 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, Colosseum Inlet received an overall score of 1.00 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 (0.97–1.00) and very good grades (A), indicating that average concentrations were well below the guideline values for this zone.
HABITATS
MANGROVE RESULTS
No mangrove assessment was conducted in 2023, results are from monitoring conducted in 2019. The overall score for Colosseum Inlet was 0.72 (B) indicating a good condition for mangroves in this zone. Mangrove extent (0.85) was very good and canopy condition (0.67) and shoreline condition (0.65) was good.
The good mangrove extent score was a result of a net gain in relative mangrove extent. This zone may benefit from being further removed from the direct impacts of clearing and development that has occurred in the more central zones.
FISH & CRABS
FISH HEALTH RESULTS
FISH RECRUITMENT RESULTS
Fish recruitment was assessed for two species: Yellowfin bream Acanthopagrus australis and Pikey bream Acanthopagrus pacificus. The overall score for 2023 was higher than the previous year (2022: 0.29, 2023: 0.41) and retained a poor (D) grade. The number of bream caught during the 2022–23 reporting period were as follows:
2022 report card: 25 fish, 2023 report card: 27 fish.
Fish health is assessed though two sub-indicators, Fish condition and Fish Health Assessment Index (HAI).
The overall score for Fish health in 2023 was 0.81 and received a good grade (B). The 2023 results were calculated by the average of the Fish HAI score (0.90; results carried over from 2021) and new assessment of Fish condition which scored similar to the previous year (2022: 0.74, 2023: 0.73).