ENVIRONMENTAL
.RESULTS
imrpoved from 2023
high
confidence
OVERALL HARBOUR .RESULTS
The following graph shows the scores received in 2024 (top line) versus the score received in 2023 for each indicator (bottom row)
Very good (0.85-1.00)
Good (0.65-0.84)
Satisfactory (0.5-0.64)
Poor (0.25-0.49)
Very Poor (0.00-0.24)
No data available
RESULTS
The overall score for the Environmental Health component was 0.67, an improvement from the 2023 score (0.63), moving from a satisfactory grade (C) to a good grade (B).
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Overall, the Water and Sediment Quality indicator group scored the same as the previous year and has consistently received a very good grade (A) for the past seven years. The 2024 Water quality indicator score and grades were similar to 2023 (0.83, remaining a good grade (B)). Sediment Quality received a very good grade (A) similar to 2023 (2023: 0.97, 2024: 0.96).
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In comparison to 2023, the Habitats indicator group received a higher overall score, but retained the same grade – poor (D). This was due to an improvement in Seagrass scores (2023: 0.58, 2024: 0.68). In both 2023 and 2024, Coral scores remained low (2023: 0.14, 2024: 0.14) corresponding to a very poor grade (E). Mangroves were assessed in 2024 and, while improving on the 2019 score (2019: 0.57, 2024: 0.63), retained a satisfactory grade (C).
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The Fish and Crabs indicator group improved in score from the previous year (2023: 0.57, 2024: 0.62) but the grade remained satisfactory (C). The Fish health indicator score and grade was similar to the 2023 results (2023: 0.81, 2024: 0.84, good grade (B)), while Fish recruitment improved in score (2023: 0.47, 2024: 0.57) and in grade, from poor (D) in 2023 to satisfactory (C) in 2024. In contrast, the Mud crabs score decreased (2023: 0.51, 2024: 0.46) and declined a grade (2023: satisfactory (C), 2024: poor (D)).
To learn more about these results and the various factors that determined each score, check out our Technical Report or FAQ sheet.
Water & Sediment Results
Fish Recruitment
Results
Seagrass
Results
Mudcrab
Results
Coral Results
Results by Harbour Zone
Mangrove Results
Fish Health
Results
WHAT WAS MEASURED?
The Environmental Health of Gladstone Harbour was assessed based on three indicator groups: Water and Sediment Quality, Habitats and Fish and Crabs.
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WATER AND SEDIMENT QUALITY
Water And Sediment Quality scores are based on 11 Water quality and 6 Sediment quality measures. Under a data-sharing agreement, the Port Curtis Integrated Monitoring Program provide GHHP with water and sediment quality data. Samples were collected from 51 sampling sites across 13 harbour zones. Water quality data collection was conducted quarterly, and sediment sampling was conducted annually in conjunction with the water quality sampling in May 2024.
HABITATS
Three indicators make up the Habitats indicator group: Seagrass, Coral and Mangroves.
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The Seagrass indicator consists of three sub-indicators: Biomass, Area and Species composition. Data is provided by TropWater at James Cook University with agreement from the Gladstone Ports Corporation and is collected from 14 seagrass meadows in six harbour zones. The monitoring is conducted annually in October/November around the annual peak of seagrass abundance.
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The Coral indicator consists of four sub-indicators: Coral cover, Change in cover, Macroalgal cover and Juvenile density. Coral monitoring is conducted annually in May at two reefs in the Outer Harbour zone and four reefs in the Mid Harbour zone.
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The Mangrove indicator consists of three sub-indicators: Mangrove extent, Mangrove canopy condition and Shoreline condition. Data were collected from the 13 harbour zones which are split into twenty-three sub-zones. Mangroves were assessed for the first time since 2019 as part of a five year monitoring repetition.
FISH AND CRABS
The Fish and Crabs indicator group consists of three indicators: Fish health, Fish recruitment and Mud crabs.
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Fish health is measured in two separate projects: the Fish Health Assessment Index (HAI) and Fish condition. The first sub-indicator (Fish HAI) provides a thorough assessment of internal and external measures of fish health. The Fish HAI sub-indicator was last assessed in 2021 and this data is used in the 2024 report card. The second sub-indicator (Fish condition) uses data collected by recreational fishers. Anglers in fishing competitions use a mobile phone app to capture an image of the fish for assessment with an object detection algorithm, as well record of fish length and weight. The data used to calculate this score were collected in the 2023–24 report card year. Data collection for both sub-indicators occur throughout the harbour and a single harbour-wide score is provided.
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The Fish recruitment indicator is based on the total catch of juveniles of two bream species (Yellowfin bream and Pikey bream). It provides a measure of juvenile fish entering the breeding population. Fish recruitment is measured in tributaries to Gladstone Harbour and includes all harbour zones except the Outer Harbour.
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Three sub-indicators of Mud crab health were assessed: sex ratio, abundance and prevalence of rust lesions. Annual mud crab monitoring is conducted in February and June in seven harbour zones.
WATER QUALITY
Overall Harbour Scores for Water quality sub-indicators
2024 (top line) 2023 (bottom line)
In the 2023 report card, the Water quality indicator score has improved slightly (2023: 0.81, 2024: 0.83), but maintained the same grade (good, B). This increase was due to higher scores for one Physiochemical measure, turbidity, and one Nutrient measure, total phosphorus. It is likely that lower-than-average rainfall during the reporting period has impacted these results.
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Within the Physicochemical sub-indicator, all zones scored very high (1.00) corresponding to a very good grade (A) for pH. In contrast, the turbidity scores varied (0.50–0.92) and grades ranged from satisfactory (C) to very good (A). All of the 13 zones were graded satisfactory (C) or above, resulting in an overall harbour score of 0.68 and a good grade (B) for turbidity.
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The overall harbour score for Nutrients (0.69) was the lowest amongst all Water quality sub-indicators and graded good (B). For Total nitrogen, all zones received poor (D) or satisfactory (C) grades (scores: 0.31–0.58). In contrast, for Total phosphorus, most zones received good (B) or very good (A) grades (scores: 0.66–1.00), with only one zone receiving a satisfactory grade (C; score: 0.60). Chlorophyll-a results were the most varied of the three Nutrient measures, with zone scores ranging from 0.37–0.90 and grades ranging from poor (D) to very good (A).
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Overall, the Dissolved metals grades in all zones were very good (A). Consistent with the previous report card, the dissolved metals measures all received high scores (0.87–1.00), except for copper in the Auckland Inlet zone which received a lower score (2023: 0.79, 2024: 0.83) and resulted in a good grade (B).
SEDIMENT QUALITY
Overall Harbour Scores for the Sediment quality sub-indicator
2024 (top line) compared to 2023 (bottom line)
The overall Sediment quality scores were derived from one sub-indicator – metals and metalloids. Six metals (cadmium, copper, lead, mercury, nickel and zinc) and the metalloid arsenic were assessed. The harbour score for Sediment quality was 0.96 and graded very good (A), similar to preceding years (0.95–0.99; very good (A)). While scores for most measures were very good, there were several good or satisfactory scores for arsenic and nickel. However, it should be noted that arsenic and nickel are naturally occurring within the harbour, hence these metals are not necessarily associated with anthropogenic inputs.
SEAGRASS
Overall Harbour Scores for Seagrass
2024 (top line) compared to 2023 (bottom line)
Overall, Seagrass received a score of 0.68 and was graded good (B). These results are a return to the 2022 report card grade (0.70; good, B), and remains a marked improvement from the overall condition observed from 2015 to 2018 (0.35–0.43; poor grade, D).
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Four zones, The Narrows, Western Basin, South Trees Inlet, and Rodds Bay were graded in a good (B) or very good (A) condition. Although recovery in biomass and area was observed in the Inner Harbour, a very poor species composition score resulted in a poor grade (D) for this zone. Mid Harbour received a lower grade (poor, D), while the Rodds Bay grade improved markedly (2023: poor, D; 2024: good, B).
Over twenty years of annual monitoring in seagrass condition around Gladstone Harbour indicates a strong relationship between seagrass condition and influences such as rainfall and river flow. Improvements in Seagrass condition in the 2024 Gladstone Harbour Report Card may be attributed to below average rainfall and decreased discharge from the Calliope River relative to previous years. It is also possible that high levels of herbivory from dugongs and turtles may be impacting the condition of some meadows such as Pelican Banks.
CORAL
Overall Harbour Scores for Coral sub-indicators
2024 results (top line) compared to 2023 (bottom line)
Coral health was monitored at six locations in Gladstone Harbour, involving four locations within the Mid Harbour reporting zone and two locations in the Outer Harbour reporting zone.
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In 2024, corals were in a very poor condition for the seventh consecutive year and received an overall score of 0.14, corresponding to a very poor grade (E). This was a result of a low cover of living coral, high macroalgal cover, low abundance of juvenile corals, and a poor overall score for change in hard coral cover. Score changes at the sub-indicator level were minor between 2023 and 2024 with all sub-indicators receiving similar scores to the previous year.
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Ongoing pressures such as high macroalgal cover and the widespread presence of the bio-eroding sponge Cliona orientalis appear to be hindering the recovery of the coral communities in Gladstone Harbour.
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Initial coral monitoring in 2015 noted very low coral cover, which reflected the severe impacts of the 2013 flooding. Subsequent monitoring has shown a lack of recovery in coral condition. Ongoing pressures such as high macroalgal cover and the prevalence of bio-eroding sponges continue to limit the recovery of these reefs. Based on various sub-indicator scores, the corals of Gladstone Harbour demonstrated limited recovery potential in 2024.
The condition of reefs in the harbour are comparable with other severely impacted reefs in Keppel Bay and the Whitsundays. Given the depleted state of coral cover, recovery will be largely dependent on connectivity with reefs beyond Gladstone Harbour.
MANGROVES
A new assessment of Mangroves was conducted in 2024. The overall score for Mangroves was 0.63, a small increase from the 2019 score (0.57), however the grade remained the same (satisfactory, C).
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Seven zones, Graham Creek, Western Basin, Boat Creek, Calliope Estuary, Boyne Estuary, Outer Harbour, and Colosseum Inlet were in good condition. Two zones, Auckland Inlet and Mid Harbour were in poor condition. Decreases in shoreline condition and mangrove extent respectively contributed to the poor grades at these two zones. In 2023–24, several issues were observed across the study area, with human activities significantly impacting developed shoreline areas near mangroves. The most affected zones were Inner Harbour, Calliope Estuary, Auckland Inlet, Mid Harbour, South Trees Inlet and Boyne Estuary, while Western Basin showed lesser but still notable human influence. These findings were consistent with previous observations from 2018 and 2019. In addition to human-induced changes, natural climatic events, such as heavy rainfall, storms, and rising sea levels, continued to influence mangrove recovery, which has been slow but steady.
FISH HEALTH
Overall Harbour Scores for Fish health sub-indicators
2024 results (top line) compared with 2023 (bottom line)
The overall score calculated for Fish health in 2024 was 0.84, corresponding to a good grade (B). This score was calculated by averaging the Fish condition score (0.78) and the Fish Health Assessment Index (HAI; 0.90). Note: the Fish HAI results have been carried over from the 2021 assessment for both the 2023 and 2024 report cards.
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Fish Condition
The overall score for Fish condition (0.78) is calculated as the aggregation of visual fish condition and fish body condition for three fish species – Yellowfin bream, Pikey bream, and Mangrove jack – in Gladstone Harbour. Visual fish condition was not calculated for Dusky flathead as sample sizes were low and insufficient data were available. In 2024, no fish body condition data was collected for Barred javelin and Dusky flathead, as these fish species were not included in the Boyne Tannum HookUp live weigh-in. This limits comparisons with scores from previous years. Visual fish condition received high scores (0.93-0.96) for four species: Yellowfin bream, Pikey bream, Barred javelin, and Mangrove jack. For fish body condition two species, Pikey bream and Mangrove jack were graded as good (B), while Yellowfin bream received a poor (D) grade.
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Fish HAI
No new assessment of Fish HAI was undertaken in 2024 and the results have been carried over from the previous assessment (2021).
The Fish HAI is comprised of scores from five fish species. Three of the five fish species monitored in 2021 scored high, Barramundi (0.98), Barred javelin (0.90), and Bream (0.98) and received very good grades (A). The remaining two species, Blue catfish and Mullet, both scored well (0.81) and received good grades (B). In general, the surveyed fish species showed very few signs of external health issues, a similar result to the Fish condition sub-indicator. Scores for internal organs were also low indicating good to very good fish health.
FISH RECRUITMENT
Overall Harbour Scores for Fish Recruitment
2024 results (top line) compared to 2023 (bottom line)
The size distribution of fish within the juvenile population gives an indication of the number of juvenile fish maturing and entering the breeding population.
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A score of 0.50 equates to a reporting year (season) at the median reference level, indicating no increase or decrease in the catch rate from the long-term average (2011–2023). In 2024, Fish recruitment scored 0.57, equating to an overall satisfactory grade (C) across the harbour. This is a return to satisfactory grade after the poor score and grade in 2023 (0.47, D). The lower score and grade from the previous year was due to a reduction in Pikey bream catch rates. In 2024, eleven of the twelve zones assessed either increased in score and grade for fish recruitment, or remained the same.
MUD CRABS
Overall Harbour Scores for Mud crab sub-indicators
2024 (top line) compared with 2023 (bottom line)
The overall score for Mud crabs in the 2024 Gladstone Harbour Report Card was 0.46 resulting in a decline to a poor (D) grade. These results are due to a decrease in sex ratio scores and very low prevalence of rust spot lesions (corresponding to high scores).
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The harbour score for abundance was low (0.32) and graded poor (D), an improvement from the very poor (E) grade in 2023. The Narrows and Boat Creek received very high scores (0.88-1.00) and very good grades for abundance. However, five zones – Graham Creek, Calliope Estuary, Inner Harbour, Auckland Inlet and Rodds Bay – received very low scores (0.00-0.21) and very poor (E) grades. Caution is required when interpreting abundance scores as catch per effort data can be highly variable.
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For sex ratio there was a general decline from the previous year’s results. Six of the seven zones received very low scores (0.00-0.20) and very poor grades (E), and one – Boat Creek – received a poor score and grade (0.25, D) – a decline from a good (B) grade in 2023. A higher proportion of females compared to males of the same size (>15 cm spine width) suggests that fishers are observing regulations for the release of female crabs. Natural factors (temperature, reproduction cycle, etc.) may also be influencing sex ratio scores and cannot be ruled out. Research is required to understand how mud crab populations are impacted by a female-dominated sex ratio.
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As with the previous year, prevalence of rust spot lesions was very low and six of the seven zones received very high scores (0.96–1.00) and very good grades (A), while one zone – Graham Creek – received a high score (0.73, B). The average incidence of rust spot lesions across all monitored zones was 0% in March 2024, and 4.5% in July 2024, considerably lower than the 37% incidence recorded in 2012 or less than half of the 22% recorded in the late 1990s.
