ENVIRONMENTAL
.RESULTS
unchanged from 2022
high
confidence
WHOLE HARBOUR .RESULTS
The following graph shows the scores received in 2023 (top line) versus the score received in 2022 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 0.63, very similar to the 2022 score (0.64), with both years receiving a satisfactory grade (C).
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 2023 Water quality indicator score and grades were identical to 2022 (0.81 and good grade (B)). Sediment Quality received a very good grade (A) similar to 2022 (2022: 0.96, 2023: 0.97).
In comparison to 2022, the Habitats indicator group received a lower overall score, but retained the same grade – poor (D). This was due to a decline in Seagrass scores (2022: 0.70, 2023: 0.58) and a lower overall grade (2022: good (B), 2023: satisfactory (C)). In both 2022 and 2023, Coral scores remained low (2022: 0.15, 2023: 0.14) corresponding to a very poor grade (E). Mangroves were not assessed in 2023 and retained the 2019 score (0.57) and satisfactory grade (C).
The Fish and Crabs indicator group scored similar to the previous year and the grade remained satisfactory (C). The Fish health indicator score and grade was consistent with the 2022 results (both years: 0.81, good grade (B)), while Fish recruitment declined in score (2022: 0.57, 2023: 0.47) and a grade (2022: satisfactory (C), 2023: poor (D)). In contrast, the Mud crabs score increased (2022: 0.39, 2023: 0.51) and resulted in an improved grade (2022: poor (D), 2023: satisfactory (C).
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 six Sediment quality measures. Under a data-sharing agreement, 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 2023.
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 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 last assessed in 2019 and this data is used for the 2023 report card.
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. Fish HAI sub-indicator was last assessed in 2021 and this data is used in the 2023 report card. The second sub-indicator (Fish condition) uses a mobile phone app to capture an image of the fish for assessment with an object detection algorithm, as well as a visual assessment and record of fish length and weight by the angler. The data used to calculate this score were collected in the 2022–23 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.
SEDIMENT QUALITY
The following graph compares the Sediment quality scores reported for 2023
(top line) to those from the previous year (bottom line).
The overall Sediment quality scores were derived from one sub-indicator – metal and metalloids. Six metals (cadmium, copper, lead, mercury, nickel and zinc) and the metalloid arsenic were assessed.
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The harbour score for Sediment quality was 0.97 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.
WATER QUALITY
The following graph compares the Water quality scores reported for 2023 (top line) to those from the previous year (bottom line).
In the 2023 report card, the Water quality indicator score was the same as the previous year, but lower compared to the 2021 report card (2021: 0.91, 2022 and 2023: 0.81). This decrease was due to lower scores for one Physiochemical measure, turbidity, and all three Nutrient measures, total nitrogen, total phosphorus and chlorophyll-a. It is likely that higher-than-average rainfall during the reporting period has impacted these results.
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 (0.19–0.91) and grades ranged from very poor (E) to very good (A). Ten of the 13 zones were graded satisfactory (C) or above and resulted in an overall harbour score of 0.67 and a good grade (B) for turbidity.
The overall harbour score for Nutrients (0.62) was the lowest amongst all Water quality sub-indicators and graded satisfactory (C). For Total nitrogen, all zones received poor (D) or satisfactory (C) grades (scores: 0.35–0.58). In contrast, for Total phosphorus, most zones received good (B) or very good (A) grades (scores: 0.68–1.00), with only two zones receiving satisfactory grades (C; scores: 0.55–0.63). Chlorophyll-a results were the most varied of the three Nutrient measures, with zone scores ranging from 0.32–0.72 and grades ranged from poor (D) to good (B).
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 (2022: 0.85, 2023: 0.79) and resulted in a reduction in grade (2022: very good (A), 2023: good (B)).
SEAGRASS
The following graph compares the Seagrass scores reported for 2023 (top line) to those from the previous year (bottom line).
Overall, Seagrass received a score of 0.58 and was graded satisfactory (C). While these results are a decline from the 2022 report card (0.70; good grade, B) it is still a marked improvement from the overall condition observed from 2015 to 2018 (0.35–0.43; poor grade, D).
Three zones, The Narrows, Western Basin and South Trees Inlet, were graded in a good (B) or very good (A) condition. Poor recovery was observed in the Inner Harbour due to low biomass and species composition, resulting in a very poor grade (E) for this zone. Mid Harbour received a lower grade (satisfactory, C) and the Rodds Bay grade remained the same (poor, D).
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. Decreases in Seagrass condition in the 2023 Gladstone Harbour Report Card may be attributed to above average rainfall and increased discharge from the Calliope River relative to previous years. Additionally, another factor impacting seagrass recovery around Gladstone Harbour, particularly in the Pelican Banks meadows, is turtle and dugong herbivory. It is likely that high levels of herbivory from dugongs and turtles may be altering the species composition and restricting recovery of this meadow.
CORAL
The following graph compares the Coral scores reported for 2023 (top line)
to those from the previous year (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.
In 2023, corals were in a very poor condition for the sixth 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 (Table 5). Score changes at the sub-indicator level were minor between 2022 and 2023 with all sub-indicators receiving similar scores to the previous year.
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.
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 2023.
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
There was no new assessment of the Mangrove indicator this year; results have carried over from the 2019 report card. The following graph shows the scores received in 2019.
There was no new assessment of Mangroves in 2023 and the results have been carried over from the previous assessment in 2019. The overall score for Mangroves was 0.57, a small decrease from the 2018 score (0.60), however the grade remained the same (satisfactory, C).
Four zones, Colosseum Inlet, Outer Harbor, Auckland Creek, and The Narrows were in good condition. Two zones Boat Creek and Boyne Estuary were in poor condition. Decreases in canopy condition at these two zones was most likely to be because of the low rainfall levels observed in the reporting year.
The Boyne Estuary also contained areas of dieback indicative of flood and erosion damage, which was first observed in the 2018 surveys. The slow recovery of mangroves in this area may have been exacerbated by access tracks, clearing and cutting of dead vegetation which is preventing and inhibiting seedling recruitment and re-establishment. The remaining seven zones all had satisfactory scores similar to those recorded in the previous year with five zones showing a slight reduction in the overall score.
FISH HEALTH
The following graph compares the Fish health scores reported for 2023 (top line)
to those from the previous year (bottom line).
The overall score calculated for Fish health in 2023 was 0.81, corresponding to a good grade (B). This score was calculated by averaging the Fish condition score (0.73) 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 2022 and 2023 report cards.
Fish Condition
The overall score for the Fish condition (0.73) is calculated as the aggregation of visual fish condition and fish body condition for five fish species in Gladstone Harbour. Visual fish condition received high scores (0.96–0.97) across all five species: Yellowfin bream, Pikey bream, Barred javelin, Dusky flathead and Mangrove jack, resulting in an overall score of 0.97, corresponding to a very good grade (A). In contrast, fish body condition received below average scores for all species (0.42–0.50) and resulted in an overall score of 0.48 and a poor grade (D) for fish body condition. These results are very similar to the previous year.
Fish HAI
No new assessment of Fish HAI was undertaken in 2023 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
The following graph compares the Fish recruitment scores reported for 2023 (top line) to those from the previous year (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.
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 (2011–2022). In 2023, Fish recruitment scored 0.47, equating to an overall poor grade (D) across the harbour. This is a notable decline from the previous year’s results (0.57 and satisfactory grade (C)).
Overall, the reduction in scores and lower grade from the previous year is due to the reduction in Pikey bream catch rates (2022: 448, 2023: 203). The dry conditions in December 2022 to February 2023 that may have impacted food supply for relevant fish species.
MUD CRABS
The following graph compares the Mud crab scores reported for 2023 (top line) to those from the previous year (bottom line).
The overall score for Mud crabs in the 2023 Gladstone Harbour Report Card was 0.51 resulting in a satisfactory (C) grade. These results are an improvement from the previous year, 0.39 and poor grade (D) and are due to an increase in sex ratio scores and very low prevalence of rust spot lesions (corresponding to high scores).
The harbour score for abundance was very low (0.13) and graded very poor (E), the lowest observed since GHHP monitoring began. Five zones – Graham Creek, Calliope Estuary, Inner Harbour, Auckland Creek and Rodds Bay – received the lowest possible scores (0.00) and very poor (E) grades. Caution is required when interpreting abundance scores as catch per effort data can be highly variable.
For sex ratio there was a general improvement from the previous year’s results. Three zones still received very low scores (0.00) and very poor grades (E). However, two zones improved from poor grades (D) to a satisfactory grade (C) for Calliope Estuary (2022: 0.29, 2023: 0.62) and a good grade (B) Boat Creek (2022: 0.43, 2023: 0.71). Another highlight is the high score (1.00) and very good grade (A) for Rodds Bay (previously not calculated due to insufficient crab data). It is important to note these scores were based on a relatively small sample of mud crabs. 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.
As with the previous year, prevalence of rust spot lesions was very low and all zones where scores could be calculated received high scores (0.88–1.00) and very good grades (A). The average incidence of rust spot lesions across all monitored zones was 0% in February 2023 and 10.3% in June 2023, considerably lower than the 37% incidence recorded in 2012 or less than half of the 22% recorded in the late 1990s.
