Colosseum Inlet
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
Grading system
Water & Sediment Quality Results
Water & Sediment Quality Results Commentary
Water quality
Colosseum Inlet received an overall water quality score of 0.89 (A). This score was based on the scores for physicochemical (0.99), nutrients (0.69) and dissolved metals (1.00).
Sediment quality
Sediment quality of Colosseum Inlet was very good with an overall score of 0.97 (A).
Measures Results
Water & Sediment Measures Commentary
Colosseum Inlet 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 (0.97) 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.
Colosseum Inlet received a good overall score for nutrients (0.69). All three sub-indicators had satisfactory or above scores, indicating that average concentrations for all three measures were below the guideline values for this zone. Total phosphorus had a very good score (1.00), total nitrogen had a satisfactory score (0.55), and chlorophyll-a had a satisfactory score (0.53).Habitats
Grading system
Mangrove Results
Mangrove Results Commentary
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 and Crabs
Grading system
Fish Health Results
| Harbour Score | |
|---|---|
| Visual fish condition (VFC) | 0.72 |
| Fish health assessment index (HAI) | 0.67 |
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 Result Commentary
Fish Health (Overall)
The overall score calculated for fish health in 2020 was 0.69 (B), which is an average of the scores for Visual Fish Condition 0.72 (B) and the Health Assessment Index 0.67 (B).
Visual Fish Condition:
The overall score for the visual fish condition is an average of 0.98 (A) for Fish Visual Assessment (FVA) and 0.46 (D) 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 0.97 (A) to 0.99 (A). This result was similar to the HAI scores for external measures where a very low number of external health issues were recorded.
The poor score for FBC in 2019 was a result of poor scores for yellow-finned bream (0.44) and pikey bream (0.48). Both species assessed had a mean body condition below the long-term average (2003 – 2019). It is possible that the lower scores for fish body condition this year and in the previous year are influenced by climate variation but further research is needed to establish this.
Fish Health Assessment Index:
The overall HAI score for Gladstone Harbour was 0.67 (B).
This was comprised of scores from three fish species, barramundi 0.55 (C), barred javelin 0.84 (B) and blue catfish 0.61 (C). While bream and mullet are also target species for this indicator, these were caught in insufficient numbers to calculate a report card score in 2020.
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 for spleen, kidney and hindgut resulting in a good report card score for barred javelin and a satisfactory score for barramundi and blue catfish.
Fish Recruitment Results
| Zone ID | Score |
|---|---|
| 12. Colosseum Inlet | 0.63 |
Fish Results Commentary
Fish recruitment was assessed for two species: yellow-finned bream Acanthopagrus australis and pikey bream Acanthopagrus pacificus. The overall score for 2020 was 0.64 (C) and scores in all zones improved. The overall score was a marked improvement from the 2019 score (0.27), which was the lowest score since fish recruitment was included in the report card in 2016. This improvement may be a response to the prevailing climatic conditions. While total rainfall in the 2019–20 reporting year was below average, rainfall in January and February 2020 was greater than the long-term monthly average. Freshwater inflows have been linked to estuarine productivity with productivity declining in drier years and the improved result may be a result of improved inflows. However, fish recruitment has been a highly variable report card indicator and further investigations are required to determine the extent of the relationship between prevailing climatic conditions and bream recruitment in Gladstone Harbour.