unchanged from 2020
WHOLE HARBOUR RESULTS
Very good (0.85-1.00)
Very Poor (0.00-0.24)
No data available
Of the three indicator groups, water and sediment quality received the highest score of 0.93 (A). This score was a result of very good water quality (0.91) and sediment quality (0.96) scores.
The overall score for the habitat indicator group was 0.48 (C). The poor habitat score was due to a good score for seagrass (0.72), a satisfactory score for mangroves (0.57) and a very poor score for corals (0.14). This is the second year in a row that seagrass has received a good grade and the fourth consecutive year coral has received a very poor score.
The overall score for the fish and crab indicator group was satisfactory 0.62 (C). The fish health score was good (0.82), the fish recruitment score was satisfactory (0.62) and the score for mud crabs was poor (0.48).
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.
WATER AND SEDIMENT QUALITY
Water and sediment quality scores are based on eleven water quality and six sediment quality measures. Water and sediment quality data were collected from 51 sampling sites across thirteen harbour zones. Water quality data collection was conducted quarterly, and sediment sampling was conducted in conjunction with the water quality sampling in May 2021.
There are three habitat indicators within the environmental component: seagrass, coral and mangroves.
The seagrass indicator consists of three sub-indicators: seagrass biomass, seagrass area and species composition. Data is collected from fourteen seagrass meadows in six harbour zones. The monitoring is conducted annually in October/November around the annual peak of seagrass abundance.
The coral indicator group consists of four sub-indicators: coral cover, coral cover change, 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.
The mangrove indicator consists of three sub-indicators: mangrove extent, mangrove canopy condition and shoreline condition. Data is collected from the 13 harbour zones which are split into twenty-three sub-zones. Mangroves were last assessed in 2019.
FISH AND CRABS
The fish and crabs indicator group consists of two fish health indicators, a fish recruitment indicator and an indicator for mud crab health.
Fish Health is measured in two separate projects:
Fish Health Assessment Index.
Visual Fish Condition.
The first project provides a thorough assessment of internal and external measures of fish health. The second project uses a mobile phone app to capture an image of the fish for assessment with an object detection algorithm, a visual assessment and length and weight is also recorded by the angler. Data collection occurs throughout the harbour and a single harbour-wide score is provided.
The fish recruitment indicator is based on the total catch of juveniles of two bream species (yellow-finned 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.
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 AND SEDIMENT
Water quality was relatively uniform across the harbour with 11 of the 13 environmental monitoring zones receiving an overall rating of very good. The remaining two zones received an overall rating of good. This was the second time the water quality indicator received an overall very good score (0.91, A) within the GHHP program.
The physicochemical scores (pH and turbidity) were very good in all 13 monitoring zones. At the measure level, scores for pH were uniformly very good (1.00). Turbidity scores were consistently good or very good (0.69 to 1.00), with most zones being ranked as very good.
Similar to previous report cards, nutrients received the lowest score (0.79) among the water quality sub-indicators. However, nutrient scores improved for the third consecutive year at most zones and overall received the highest score since GHHP monitoring began in 2015. Nine of the 13 monitoring zones had good scores ranging from 0.69 to 0.82. The remaining four zones had very good scores ranging from 0.86 to 0.91. At the measure level, total phosphorus received the highest scores, total nitrogen received the lowest scores, and chlorophyll-a scores were more variable, ranging from 0.48 to 0.99.
All 13 environmental monitoring zones had consistently very good scores (0.96–1.00) for dissolved metals overall. The same was true at the measure level as four of the six metals received very good scores across the 13 zones. The exceptions—copper at Boyne Estuary (0.79) and manganese at Boat Creek (0.84)—showed good scores, with the remaining twelve zones for the two measures showing consistently very good scores.
Sediment quality scores were very good across all zones of Gladstone Harbour owing to low concentrations of all measures (arsenic, cadmium, copper, lead, mercury, nickel and zinc). 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.
The overall condition of monitored seagrass meadows in Gladstone Harbour was good (0.72) in the 2021 report card year. This is the second year of good condition and third consecutive year showing substantial recovery from the overall poor condition from previous report cards (2015–2018).
At the zone level, overall condition scores were satisfactory or above for five of the six zones—The Narrows, Western Basin, Inner Harbour, South Trees Inlet, and Rodds Bay. Only the Mid Harbour was in poor condition, however, this slightly improved compared to the previous year. Overall, 13 of the 14 monitored meadows were in satisfactory, good, or very good condition.
As in the preceding two report card years, results suggest that the dry, benign weather conditions provided ideal conditions for seagrass recovery in the 2021 report card year. Seagrass meadows in Gladstone Harbour started 2021 with a high level of resilience to external pressures, both natural and anthropogenic. As such, seagrasses should be well placed to cope with forecast La Niña weather patterns and anthropogenic pressures in the 2022 reporting year.
The overall condition of monitored seagrass meadows in Gladstone Harbour was good (0.79) in the 2020 report card year. This is the second year of substantial recovery from the overall poor condition from previous report cards (2015–2018). Moreover, the overall seagrass condition in 2020 was the best in the past decade of monitoring.
At the zone level, overall condition scores improved at six of the seven monitoring zones from the previous report card. The same six zones were graded good or very good, with Rodds Bay monitoring meadows in very good condition for the first time since 2009. Only the Mid Harbour showed a decreased score compared to the previous year. Overall, 13 of the 14 monitored meadows were in satisfactory, good or very good condition, with nine of these meadows improving to pre-2010 condition.
As in 2019, results suggest that the dry, benign weather conditions provided ideal conditions for seagrass recovery in the 2020 report card year. Gladstone Harbour monitored seagrass meadows are currently recovering following several years of poor condition. The overall positive improvements shown in six of the monitored zones provides a strong foundation for seagrass communities in the Gladstone area.
The overall score for mangroves was 0.57 (C), a small decrease from the 2018 score. This is a possible reflection of impacts on canopy condition from lower rainfall and delayed impacts from flooding. This is reflected in the decline in the overall harbour score for canopy condition and to a lesser extent for shoreline condition.
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.
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 0.96 (A) for Fish Visual Assessment (FVA) and 0.52 (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 in 2021 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.
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 – 2021). For 2021 fish recruitment scored 0.64 equating to an overall grade of C for fish recruitment across the harbour. This is an increase in catch rate compared to the long-term average and is a strong improvement on last year’s score of 0.27.
The overall score for mud crabs in Gladstone Harbour was 0.48 (D) indicating a poor condition. Please note, mud crabs are a novel indicator developed specifically for GHHP. Greater confidence in this indicator will develop over time.
The harbour score for abundance was poor (0.45). As in previous years the abundance scores ranged from very good to very poor. Half of zones received satisfactory or above grades—The Narrows (1.00), Boat Creek (0.83) and the Inner Harbour (0.63). The remaining four zones received poor or very poor scores (0.00–0.27). Caution is required when interpreting abundance scores as CPUE data can be highly variable.
Sex ratio received very poor scores (0.00–0.14) in five of the six zones where this measure was calculated. The exception—Calliope Estuary—received a satisfactory score (0.57. It is important to note this score was based on a relatively small sample of mud crabs. A general pattern of predominantly very poor has been evident since 2017. Results indicate a higher proportion of females compared to males of the same size (>15 cm spine width). This pattern suggests that fishers are observing regulations for the release of female crabs. Natural factors (temperature, reproduction cycle, etc.) may also be influencing scores and cannot be ruled out. Research is required to understand how mud crab populations are impacted by a female-dominated sex ratio.
Prevalence of rust spot lesions was very low in most zones, with five zones receiving very good scores (0.89–1.00). In contrast, the Inner Harbour received a poor score (0.45) for this sub-indicator. The average incidence of rust spot within the harbour was about 10%, considerably lower than the 37% incidence recorded in 2012 or less than half of the 22% recorded in the late 1990s.