13

Rodds Bay

AREA 70.14 km2
 Overall Result

Rodds Bay is located to the south-east of the Outer Harbour Zone. It is connected to Colosseum Inlet by a narrow channel behind Hummock Hill Island. The eastern side of Rodds Bay includes a number of mangrove islands. The creeks that flow into the bay are also mangrove-lined and contain large areas of salt pans. This zone includes three monitored seagrass meadows and the Rodds Bay Dugong Protection area. This is a relatively pristine zone that has significant biodiversity value.

This zone has three water and sediment monitoring sites, three seagrass monitoring meadows, four fish monitoring sites, one mud crab monitoring site and four mangrove monitoring sub-zones.

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
Rodds Bay received an overall water quality score of 0.96 (A). This score was based on the scores for physicochemical (1.00), nutrients (0.87) and dissolved metals (1.00).

Sediment quality
Sediment quality of Rodds Bay was very good with an overall score of 0.98 (A).


Measures Results

Water
Sediment

Rodds Bay 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 (1.00) 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.

Rodds Bay received a very good overall score for nutrients (0.87). Total phosphorus (1.00) and chlorophyll-a (0.85) had very good scores and total nitrogen had a good score (0.76), 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

Seagrass Results

Meadow ID Biomass Area Species Composition Overall Meadow Score Overall Zone Score
94 0.84 0.87 0.99 0.84 0.70
96 0.75 1.00 0.97 0.75 0.70
104 0.51 0.86 0.83 0.51 0.70

There are three intertidal monitoring meadows in Rodds Bay—Meadows 94, 96 and 104.

The overall condition of this zone was good (0.70) in 2021. This was a decrease from the previous year when Rodds Bay received the best overall condition score of the past decade. All three meadows showed a decreased score compared to the previous year.

Similarly, there was a general pattern in scores among sub-indicators. Area and species composition remained very good (0.86–1.00) at all three meadows, excluding species composition at Meadow 104 which received a good score (0.83). Likewise, biomass had the lowest of the three sub-indicator scores with Meadows 94 and 96 scored as good (0.84 and 0.75) and Meadow 104 scored as satisfactory (0.51).

Mangrove Results

The overall score for Rodds Bay was 0.64 (C) indicating a satisfactory condition for mangroves in this zone. Mangrove extent (0.68) and shoreline condition (0.67) were good while canopy condition was satisfactory. This zone may benefit from being further removed from the direct impacts of clearing and development that occurred in the more central zones.

The overall score in Rodds Bay declined from 0.71 (B) in 2018 to 0.64 in 2019 as a result of a fall in canopy condition. This change may reflect the impacts off decreased rainfall over the reporting year.

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
13. Rodds Bay 0.51

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

Rodds Bay is located to the south-east of the Outer Harbour zone. The eastern side of Rodds Bay includes a number of mangrove islands. The creeks that flow into the bay are mangrove-lined and contain large areas of salt pans.

The overall zone score for Rodds Bay was 0.56 indicating a satisfactory condition for mud crabs. This score was the highest recorded since monitoring began. Abundance was very poor (0.16) and prevalence of rust lesions was very good (0.96). The overall satisfactory score was largely driven by a satisfactory sex ratio score (0.57); however, it is important to note this sub-indicator score was derived from a relatively small sample of crabs (n = 19).