South Trees Inlet
South Trees Inlet is a mangrove and salt pan-lined tidal inlet that flows into the Mid Harbour Zone. The zone contains one monitored seagrass meadow which sits just off the northern tip of South Trees Island. At 10.9ha it is the second smallest of the monitored meadows. The area contains a large number of industrial developments, including South Trees Wharf on South Trees Island at the inlet’s mouth, Queensland Alumina Ltd to the west of the inlet, and Boyne Smelters to the south-west of the inlet. The South Trees Industrial Estate is located next to Wapentake Creek which flows into the western side of the inlet just south of South Trees Island.
This zone has six water and sediment monitoring sites, three monitored seagrass meadows, three fish monitoring sites and one mangrove monitoring sub-zone.
Water & Sediment
Water & Sediment Quality Results
Water & Sediment Quality Results Commentary
South Trees Inlet received an overall water quality score of 0.91 (A). This score was based on the scores for physicochemical (0.99), nutrients (0.77) and dissolved metals (0.98).
Sediment quality of South Trees Inlet was very good with an overall score of 0.97 (A).
Water & Sediment Measures Commentary
South Trees 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 (0.85–1.00) indicating that average concentrations were well below the water quality guideline values.South Trees Inlet received a good overall score for nutrients (0.77). Total phosphorus had a very good score (0.99), total nitrogen had a good score (0.73), and chlorophyll-a had a satisfactory score (0.59), indicating that average concentrations for these measures were below the guideline values for this zone.
|Meadow ID||Biomass||Area||Species Composition||Overall Meadow Score||Overall Zone Score|
Seagrass Results Commentary
This zone has one monitored meadow which sits off the northern tip of South Trees Island. Meadow 60 is an intertidal meadow and the second smallest of the monitored meadows.
The overall condition of South Trees Inlet’s single meadow remains very good (0.97), with all three sub-indicators in very good condition for the fourth consecutive year. This marks the fifth year of improved seagrass condition from the overall poor condition in 2016.
Record meadow area was recorded in 2021, with the meadow covering ~12.7 hectares. Biomass scored very good (0.97) for the fourth consecutive year. Moreover, the historically dominant species of seagrass covered 100% of the meadow for the first time in six years.
Mangrove Results Commentary
The overall score was 0.60 indicating a satisfactory condition for mangroves. Canopy condition (0.50) and shoreline condition (0.51) were satisfactory. Mangrove extent (0.79) received a good score, a result of a net gain in relative mangrove area. However, it is important to note that the health of mangroves is being measured from a 2013-14 baseline and considerable clearing and habitat modification has occurred in these areas in the past.
Fish and Crabs
Fish Health Results
|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 Result Commentary
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
|9. South Trees Inlet||0.47|
Fish Results Commentary
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.