Boyne River Estuary
The Boyne River is dammed at Lake Awoonga to provide potable water for the Gladstone area. Large numbers of barramundi are stocked in Lake Awoonga and may be introduced into the Boyne Estuary when the dam overtops. The Boyne Estuary was the site of large-scale mortality of many of these introduced barramundi and other fish in 2011. The lower reach of the Boyne River flows from the dam through predominately agricultural land that has pockets of remnant vegetation. Before entering the south-eastern section of the Mid Harbour Zone the Boyne River flows through the residential communities of Boyne Island and Tannum Sands.
This zone has one water and sediment monitoring site, two fish monitoring sites and one mangrove monitoring sub-zone.
Water & Sediment
Water & Sediment Quality Results
Water & Sediment Quality Results Commentary
Boyne Estuary received an overall water quality score of 0.87 (A). This score was based on the scores for physicochemical (0.94), nutrients (0.71) and dissolved metals (0.96).
Sediment quality of Boyne Estuary was very good with an overall score of 0.99 (A).
Water & Sediment Measures Commentary
Boyne Estuary 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 (0.88) indicating that average turbidity was well below the guideline value.
All six dissolved metals received good or very good scores (0.79–1.00) indicating that average concentrations were below the water quality guideline values.Boyne Estuary received a good overall score for nutrients (0.71). Total phosphorus had a very good score (1.00) and chlorophyll-a had a good score (0.73), indicating that average concentrations for these measures were below the guideline values for this zone. In contrast, total nitrogen had a poor score (0.40) as the average concentration was above the guideline value.
Mangrove Results Commentary
The overall condition of mangroves in Boyne Estuary was 0.26 (D), indicating a poor condition. While mangrove extent (0.39) was poor both canopy condition (0.19) and shoreline condition (0.19) were very poor.
The score for Boyne Estuary fell from 0.41 in 2018 to 0.26 in 2019. This was largely a result of changes in canopy condition where the score declined from 0.49 in 2018 to 0.19. This may reflect the impacts off decreased rainfall over the reporting year.
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
|10. Boyne River Estuary||0.53|
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.