4

Boat Creek

AREA 0.75 km2
 Overall Result

Boat Creek is a small mangrove-lined estuary connected to the western side of the Western Basin. This long (approximately 9km), narrow water body is not well flushed during regular tides. It is a small zone that only includes approximately 2km of waterway and a small open harbour area near the mouth.

This zone has three water and sediment monitoring sites, one fish monitoring sites, a mud crab monitoring site and one mangrove monitoring sub-zone.

Water & Sediment

Grading system
A
Very good (0.85-1.00)
B
Good (0.65-0.84)
C
Satisfactory (0.50-0.64)
D
Poor (0.25-0.49)
E
Very poor (0.00-0.24)
 
Data not available

Water & Sediment Quality Results

Water
Sediment

Water quality
Boat Creek received an overall water quality score of 0.84 (B). This score was based on the scores for physicochemical (0.85), nutrients (0.69) and dissolved metals (0.97).

Sediment quality
Sediment quality of Boat Creek was very good with an overall score of 0.92 (A).


Measures Results

Water
Sediment

Boat Creek 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 good score for turbidity (0.69) indicating that average turbidity was below the guideline value.

All six dissolved metals received good or very good scores (0.84–1.00) indicating that average concentrations were below the water quality guideline values.

Boat Creek received a good overall score for nutrients (0.69). Total phosphorus (0.59) and total nitrogen (0.50) has satisfactory scores and chlorophyll-a had a very good score (0.97), indicating that average concentrations for these measures were below the guideline values for this zone.

Habitats

Grading system
A
Very good (0.85-1.00)
B
Good (0.65-0.84)
C
Satisfactory (0.50-0.64)
D
Poor (0.25-0.49)
E
Very poor (0.00-0.24)
 
Data not available

Mangrove Results

The overall zone score for Boat Creek was 0.46 (D) indicating a poor condition. Mangrove extent (0.54) was satisfactory and canopy condition (0.38) and shoreline condition (0.46) were poor.

The overall score for Boat Creek fell from 0.63 in 2018 to 0.46 in 2019. This was largely a result of changes in canopy condition where the score declined from 0.61 in 2018 to 0.38 and a decline in shoreline condition from 0.63 to 0.46 in 2019. This may reflect the impacts off decreased rainfall over the reporting year and increased shoreline erosion.

Fish and Crabs

Grading system
A
Very good (0.85-1.00)
B
Good (0.65-0.84)
C
Satisfactory (0.50-0.64)
D
Poor (0.25-0.49)
E
Very poor (0.00-0.24)
 
Data not available

Fish Health Results

Harbour Score
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 (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

Zone ID Score
4. Boat Creek 0.35

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.

Mud Crabs Results

Boat Creek is a small mangrove-lined estuary connected to the western side of the Western Basin.

The overall zone score for Boat Creek was 0.60 indicating a satisfactory condition for mud crabs. While lower than the 2020 score of 0.71, the 2021 score at Boat Creek was still an improvement from scores received in 2018 and 2019 (0.48–0.51). In 2020, abundance received a good score (0.83) and sex ratio received a very poor score (0.03). Both sub-indicators had higher lower scores than the previous year. In contrast, the very good score for prevalence of rust lesions (0.84) indicated a very low incidence of this condition in Boat Creek. This score was higher than in the previous year.