Environmental: Indicator Group Results

Whole Harbour

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 seven 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.

Habitats

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:

  1. Fish Health Assessment Index
  2. 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, as well as a visual assessment and record of fish length and weight 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.


Results

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).

Environmental Indicators
2021 Results
Environmental Overall Result
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

Confidence
Confidence
Change (from 2020 to 2021)
Change

  Water & sediment

What Was Measured?

Three sub-indicators were used to assess water quality—physicochemical, nutrients and dissolved metals—which were comprised of eleven measures.

  1. Physicochemical: pH and Turbidity
  2. Nutrients: Total Nitrogen (TN), Total Phosphorus (TP) and Chlorophyll-a
  3. Dissolved metals: Aluminium (Al), Copper (Cu), Lead (Pb), Manganese (Mn), Nickel (Ni) and Zinc (Zn)

One sub-indicator was used to assess sediment quality—metals and metalloid—which was comprised of seven measures.

  1. Metals and metalloid: Arsenic (As), Cadmium (Cd), Copper (Cu), Lead (Pb), Mercury, (Hg) Nickel (Ni) and Zinc (Zn)

Please refer to the 2021 GHHP Technical Report for more information on the measures listed above.


Why Was It Measured?

Water and sediment quality are important and interconnected aspects of the harbour ecosystem. Healthy water and sediment are necessary to sustain a variety of marine life. Many environmental and human-related factors play a role in determining the water and sediment quality of the harbour.

The Gladstone Harbour Report Card uses standard measures for water and sediment quality that were recommended by the Independent Science Panel. All eighteen water and sediment quality measures have local or national guidelines. Data used to determine water and sediment quality scores and grades for the 2021 report card were provided by the Port Curtis Integrated Monitoring Program. Water quality data is collected quarterly from 51 sites across 13 harbour zones. Sediment quality data is collected annually from the same sites.


What Does It Mean?

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.

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

Measures Results

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

Measures Results

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

Measures Results

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

Measures Results

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

Measures Results

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

Measures Results

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

Measures Results

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

Measures Results

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

Measures Results

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

Measures Results

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

Measures Results

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

Measures Results

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

Measures Results

Water
Sediment

  Habitats

Seagrass Results

What Was Measured?

Seagrass meadows in Gladstone Harbour are located in The Narrows, Western Basin, Inner Harbour, Mid Harbour, South Trees Inlet and Rodds Bay. Three sub-indicators of seagrass health were measured to calculate the seagrass score for the 2021 Gladstone Harbour Report Card:

Biomass: Average above-ground biomass within a monitoring meadow.

Area: Total area of a monitoring meadow.

Species composition: Relative proportions of different seagrass species within a monitoring meadow. Meadows with a higher proportion of historically dominant species receive higher scores.

Meadow condition is defined as the lowest sub-indicator score when this score is either meadow area or biomass. Where species composition is the lowest score, the overall meadow score is 50% of the species composition score and 50% of the next lowest score (area or biomass).

The zone grade was measured as the average grade of the meadows within that zone.


Why Was It Measured?

Seagrass meadows are one of Gladstone Harbour’s most important habitat types. There are 14 seagrass meadows monitored in six harbour zones within the GHHP reporting area. The area and distribution of seagrass meadows can vary on an annual basis and at peak distribution seagrass meadows in Gladstone Harbour can cover an area of approximately 12,000 ha. The seagrass meadows provide a range of important ecosystem functions such as sediment stabilisation, nutrient cycling and carbon sequestration. They also provide nursery areas for juvenile fishes and foraging areas for dugongs, turtles and large fish such as barramundi.

Seagrass meadows have been monitored in Gladstone Harbour since 2002. Nearly two decades of monitoring and research has provided insight into potential causes and trends regarding changes in the seagrass meadows of Gladstone Harbour.


What Does It Mean?

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.

Corals Results

What Was Measured And Why?

Coral communities are iconic components of marine ecosystems in Australia. They provide spawning, nursery and feeding areas a variety of marine animals. Corals also provide important ecosystem services such as nutrient recycling and carbon fixation. In addition to their ecological value, coral reefs have considerable social and economic importance.

The coral indicator consists of four sub-indicators: coral cover, macroalgal cover, juvenile density and hard coral cover change. Corals in Gladstone Harbour have been monitored by GHHP for five years.

Coral cover

High coral cover suggests that a large breeding population is available, which increases its recovery potential and that of neighbouring reefs. High coral cover also contributes to a reef’s structural complexity and biodiversity by providing habitat for fishes and other marine creatures. This sub-indicator is used predominantly to inform on the state of a reef.

Macroalgal cover

Macroalgae include large fleshy species of red algae, brown algae and green algae. When abundant, macroalgae occupies space otherwise available for corals and shades the corals, thus inhibiting coral recruitment and growth. As macroalgae have a negative impact on coral, high macroalgal cover is indicative of poor coral reef condition and low macroalgal cover is indicative of good condition.

Juvenile coral density

Recovery of coral reefs from disturbances such as flooding, cyclones, bleaching or outbreaks of crown-of-thorns starfish is dependent on the recruitment of new coral colonies. Higher juvenile density indicates greater coral recruitment levels. Hence juvenile coral density can provide an indication of a reef’s recovery potential.

Hard coral cover change

Hard coral cover change is assessed by measuring the rate at which at which hard coral cover increases and provides a direct measure of recovery potential. This sub-indicator captures the coral growth rate by comparing the observed rate of change (where there is no acute disturbance) to the rate of change observed from other nearshore reefs.


What Does It Mean?

In 2021, the coral communities in Gladstone Harbour were in very poor condition. The overall grade for corals remained an E (0.14) for the fourth consecutive year. This was a result of low coral cover, low juvenile density, high macroalgal cover and a poor overall score for hard coral cover change at most of the surveyed reefs. When compared to the previous year, the slightly lower harbour score in 2021 was driven by declines in macroalgae cover and change in hard coral cover scores.

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 2021.

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.


Mangrove Results

Why Was It Measured?

Mangroves are coastal ecosystems consisting of flowering trees and shrubs adapted to marine and estuarine conditions. Exposed breathing roots, salt-excreting leaves and live water-dispersed propagules help mangroves to cope with tidal inundation and salt saturated, oxygen poor soils.

Mangroves provide valuable habitat for important aquatic species like barramundi, mud crab, and prawns. The canopy provides numerous niches for bird species, roost sites for flying foxes and feeding areas for small mammals. Mangroves provide vital ecosystem services. Coastal mangroves protect seagrass and coral communities by filtering catchment runoff and limiting shoreline erosion by reducing wave energy. Mangroves are highly productive and have a high capacity for carbon storage.

Owing to their environmental importance mangroves are protected in Queensland under the Queensland Fisheries Act 1994.

As variation in mangrove scores is likely to be small from year to year in response to changes to climatic conditions such as wet or dry years and/or changes in sea level. Mangrove monitoring will move to a 5-year cycle with the next scheduled mangrove monitoring to occur in 2024. The results form monitoring conducted in 2020 will be used to calculate the overall Environmental score in 2021 and in subsequent report cards until the next round of monitoring.


What Was Measured?

Three indicators—mangrove extent, canopy condition and shoreline condition are used to assess mangrove health.

Mangrove extent

Tidal wetlands often occupy soft sediment tidal slopes between mean sea level and highest tide level. These wetlands consist of mangroves, salt marsh and salt pans with the relative proportion of wetland occupied by each group being influenced by climate, particularly rainfall and sea level. For example, a reduction in rainfall can lead to a reduction in the area of wetland occupied by mangroves.

Report card scores for this indicator are based on satellite imagery from which the proportions of mangroves and salt marsh/salt pans is determined. A net gain in the proportion of a wetland occupied by mangroves will result in a good score and a loss of mangrove area results in a poorer score.

Mangrove canopy condition

Mangrove canopy density, measured across a forest, provides an indication of current mangrove health. Healthy forests typically have a dense canopy cover. However local or regional impacts such as changes in long-term rainfall or sea level, localised herbivory, altered hydrological regimes, increased sediment, and nutrient loads and localised pollution events can result in a decline in canopy density.

Report card scores for this indicator are derived from satellite imagery. A high score indicates a dense canopy in good condition while a low score indicates a sparse canopy in poor condition.

Shoreline condition

Shoreline mangroves can respond rapidly to changes in water quality, climate, and tidal conditions. They provide a valuable indicator of mangrove health.

Shoreline condition was assessed using aerial photographs of the shoreline taken from a helicopter. At each 50 m interval of the shoreline the presence or absence of dead mangroves was noted. Those zones with a significantly higher number of dead mangroves received a poor score and those with a significantly lower number of dead mangroves received a good score.


What Does It Mean?

Due to the stability of the mangroves indicator, this indicator was last assessed in 2019.

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.


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
21 0.84 0.99 0.93 0.84 0.84

Mangrove Results

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

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
4 1.00 0.97 0.91 0.94 0.75
5 0.86 0.82 0.82 0.82 0.75
6 0.88 0.94 0.62 0.75 0.75
7 0.63 0.74 1.00 0.63 0.75
8 0.86 0.69 0.57 0.63 0.75
52-57 0.71 0.95 1.00 0.71 0.75

Mangrove Results

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

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
58 0.59 0.91 0.60 0.59 0.59

Mangrove Results

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

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

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
43 0.33 0.87 0.50 0.33 0.48
48 0.64 0.72 0.97 0.64 0.48

Corals Results

The 2021 Gladstone Harbour Report Card scores for the Mid Harbour are based on data collected from four reefs: Facing Island, Farmers Reef, Manning Reef and Rat Island.

Mangrove Results

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
60 0.97 1.00 1.00 0.97 0.97

Mangrove Results

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

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

Corals Results

The 2021 Gladstone Harbour Report Card scores for the Outer Harbour zone are based on data collected from two reefs: Seal Rocks North and Seal Rocks South.

Mangrove Results

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

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

Mangrove Results

  Fish and Crabs

Fish Health Results

Why Was It Measured?

Fish are one of the most important social, economic and ecological resource in Gladstone Harbour. As a result, they were identified as a major concern at community workshops conducted by GHHP in 2013 to develop a community vison for the Gladstone Harbour Report Card.

Recreational fishing in Gladstone occurs throughout the harbour and is both boat and shore based. Fishing, particularly for barramundi also occurs in nearby Lake Awoonga which is regularly stocked by Gladstone Area Water Board. In 2019 the value of recreational fishing in Gladstone was estimated at nearly 27 million dollars. Commercial fishing in Gladstone includes net, pot, line and trawl fishing.

Fish play a multitude of roles in aquatic ecosystems including nutrient cycling, ecosystem regulation and bioturbations. Fish are important in nutrient cycling as they store a large proportion of ecosystem nutrients like phosphorus and nitrogen in their tissue and they transport nutrients further than other aquatic animals. The nutrients they excrete are readily available to primary producers such as algae or seagrass.


What Was Measured?

The fish health grades and scores are generated from two separate fish health monitoring projects:

  1. Visual Fish Condition: An automated visual assessment is made from images captured by fishers using a mobile phone app. Length and weight data are also recorded at the time of capture.
  2. Fish Health Assessment Index: A thorough assessment of the health of individual fish based on visual condition and the condition of several organs and tissues.

Data for Visual Fish Condition was collected by fishers at the ABT Bream tournament, members of the Gladstone Sports Fishing Club, members of the public reporting recaptures of tagged fish and Infofish Australia. Based on machine learning algorithms the trackmyfish app assesses a photo of individual fish for five indicators of visual health.

Scores for Visual Fish Condition (FVC) were determined for five fish species; yellow-finned bream, pikey bream, barred javelin, dusky flathead and mangrove jack.

Scores for VFC are based on two separate metrics; a visual assessment of fish health which includes skin, eyes, fins parasites and deformities (fish visual assessment FVA) and Fish Body Condition (FBC). FBC is calculated from length and weight data recorded at the time of capture. Measures of body condition are widely used to assess the health of individual or groups of fish. Generally, fish that are heavier than average for their length are considered healthier with more energy reserves for normal activities.

Survey work for the Fish Health Assessment Index (HAI) was conducted across Gladstone Harbour in Spring 2020 and Autumn 2021 using gill nets. Fish were photographed, measured and examined for abnormalities, parasites, lesions or erosion. While most fish were released alive at the point of capture up to 25 of each of the target species were retained for laboratory analysis.

The HAI was calculated from scoring and summing visual inspection scores for the following external and internal measures, skin, eyes, fins, gills spleen, kidney, hindgut, liver and parasite load. In 2021 a harbour wide HAI was determined for five fish species or groups: barramundi, breams. barred javelin, blue catfish and mullet.

Owing to fish movements the overall score for fish health is calculated at the harbour level. The single harbour score is necessary as fish are mobile and the health of the monitored species can not necessarily be attributed to individual monitoring zones. However, except for barramundi which move large distances, the range of movements in the remaining target species are suitable for the assessment of Gladstone Harbour as a whole.

Fish have been examined from the north, central and southern harbour areas. This provides a good spatial coverage that includes developed and undeveloped areas of the harbour. As the location of each fish captured is recorded it will be possible to identify any fish health ‘hot spots’ using this approach.


What Does It Mean?

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 0.96 (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.


Fish Recruitment Results

Why Was It Measured?

The fish recruitment indicator is based on the total catch of juveniles of two bream species (yellow-finned and pikey bream).

Fish recruitment is defined as the number of juvenile fish entering the mature fish population each year. Fish recruitment is one of the key dynamic functions that affects fish populations.


What Was Measured?

Counts of two juvenile bream species were recorded monthly at 26 sites across 12 harbour zones between December 2020 and February 2021. Fish with a tail-fork length of 100 mm or less were classified as juvenile.

To determine fish recruitment grades and scores, a statistical model was developed that relates previous results (2015 – 2020) to the annual catch rate per trip and per site and incorporates seasonal and other relevant environmental variables. The recruitment indicator scores are determined from this model, which is updated on an annual basis.


What Does It Mean?

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.


Mud Crab Results

Why Was It Measured?

Mud crabs are one of Gladstone Harbour’s iconic species. They were identified as a major community concern at workshops conducted by GHHP in 2013 due to their value to commercial and recreational fishers and the reported high rates of rust spot disease. Mud crabs spend most of their adult lives in burrows in estuarine mangrove habitats. Their abundance, size distribution and health are related to environmental conditions and fishing pressures within these habitats. This is the third year that mud crab indicators have been included in the report card.


What Was Measured?

Three sub-indicators were selected for the report card: abundance, sex ratio and prevalence of rust lesions.

Abundance

Abundance is used to estimate the number of mud crabs within a given area. This sub-indicator is indirectly measured as catch per unit effort (CPUE), which is the total catch divided by the number of crab pots. Changes in abundance may indicate changes in fishing pressure, habitats or recruitment levels. However, CPUE data can be highly variable. Catch may be impacted by capture technique, sampling area and time, or owing to differences in crab distribution, growth or survival.

Sex ratio

The sex ratio sub-indicator assesses the ratio of legal-size male crabs (>15 cm spine width) to female crabs of the same size. In Queensland mud crab fisheries, it is illegal to take female crabs. Therefore, changes in the ratio of male to female crabs may indicate changes in fishing pressures. This can alter population dynamics and may cause changes in ecosystem processes, as only male crabs dig burrows and female crabs often migrate offshore to spawn.

Prevalence of rust lesions

Rust spots (shell lesions) were first reported in Gladstone Harbour by commercial fishers in 1994. The disease is not infectious; it has been suggested that it may be related to exposure to copper and zinc, which inhibit calcium uptake. However, this relationship has not been demonstrated experimentally. The prevalence of rust spot is calculated by comparing the number of crabs with rust lesions to the total number of mud crabs caught at each monitoring zone.


What Does It Mean?

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.

Results


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 Recruitment Results

Zone ID Score
1. The Narrows 0.54

Mud Crabs Results

The Narrows is lined by mangroves and saltmarsh, provides sheltered water for mud crabs and is an important area for recreational and commercial mud crab fishers.

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 Recruitment Results

Zone ID Score
2. Graham Creek 0.84

Mud Crabs Results

Graham Creek is a mangrove-lined tidal inlet located near the south-west corner of Curtis Island. It is approximately 9 km long and flows into the southern end of The Narrows.

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 Recruitment Results

Zone ID Score
3. Western Basin 0.94

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 Recruitment Results

Zone ID Score
4. Boat Creek 0.35

Mud Crabs Results

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

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 Recruitment Results

Zone ID Score
5. Inner Harbour 0.61

Mud Crabs Results

The Inner Harbour is located immediately to the east of the Western Basin and is bounded by mangroves on Curtis Island and the town of Gladstone on the southern edge.

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 Recruitment Results

Zone ID Score
6. Calliope River Estuary 0.68

Mud Crabs Results

Calliope Estuary is fed by Gladstone Harbour’s largest freshwater catchment. Main tributaries of the Calliope River include Oakey, Paddock, Double and Larcom creeks.

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 Recruitment Results

Zone ID Score
7. Auckland Inlet 0.63

Mud Crabs Results

Auckland Inlet is a tidal inlet that connects to the Inner Harbour through a complex network of small streams meandering through mangrove-lined mudflats that are often inundated at high tide.

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 Recruitment Results

Zone ID Score
8. Mid Harbour 0.78

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 Recruitment Results

Zone ID Score
9. South Trees Inlet 0.47

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 Recruitment Results

Zone ID Score
10. Boyne River Estuary 0.53

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 Recruitment Results

Zone ID Score
11. Outer Harbour ND

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 Recruitment Results

Zone ID Score
12. Colosseum Inlet 0.56

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 Recruitment Results

Zone ID Score
13. Rodds Bay 0.51

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.