The latest test results from Gladstone Harbour have found no significant change in water quality, no single cause for all fish health issues and a decrease in the number of barramundi with eye problems or lesions.
Reports on water quality sampling, laboratory testing of fish samples and fish health surveys were released by the Department of Environment and Resource Management (DERM) and Fisheries Queensland today.
Fisheries Queensland Habitat and Assessment General Manager Dr John Robertson said department observers went out with commercial fishers again in January and February to continue monitoring fish health and collect samples.
“There’s a noticeable decrease in the number of barramundi with eye problems and lesions, and skin discolouration is also not to the extent seen previously,” Dr Robertson said.
“The majority of other fin fish species are in good condition, although sharks are still being observed with skin discolouration and naturally-occurring parasites.
“Of the 185 crabs in the Narrows and 170 crabs at Turkey Beach we caught in January, 5 per cent displayed shell abnormalities, which is similar to levels observed in historical studies.
“A total of 40 kg of prawns were caught in the Harbour and a further 60 kg of prawns outside the Harbour, with all prawns in good condition.”
Dr Robertson said further laboratory testing of fish, mollusc and crustaceans had been carried out in the Gladstone area as part of Fisheries Queensland’s ongoing investigation.
“So far, 80 submissions have been received for laboratory testing, including veterinary pathology assessment and chemical residue testing, however no single cause has been identified for all fish health issues,” Dr Robertson said.
“The identified conditions are naturally occurring organisms including a parasitic flatworm affecting barramundi, a different flatworm found on sharks and bacteria causing shell erosion on some crustaceans.
“The parasite previously reported on sharks has been identified as Dermophthirius maccallumi which occurs naturally in marine waters.
“Further testing was also undertaken on shark samples to investigate skin discolouration, however no bacterial or fungal pathogens which could explain the skin conditions were found.
“The shell erosion observed in mud crabs and prawns was consistent with bacterial infection by Vibrio spp., which also occurs naturally in marine waters.
“We also continue to test a wide range of bony fish, apart from barramundi, with mild skin abnormalities, but no bacterial, parasitic or fungal pathogens were found that explain the skin conditions.
“To more fully analyse the results in line with the Scientific Advisory Panel’s recommendations, we are expanding the sampling across a range of sites.”
Dr Robertson said the test results included findings of the investigation into the fish kill in December 2011 at Port Curtis.
“Based on observations of jewfish and ghost grinner from the fish kill, the cause of death was most likely due to the fish being caught by fishers and subsequently discarded as bycatch,” he said.
“Chemical residue analysis was also conducted on barramundi, river jewfish, prawns, mullet, whiting and scallops from inside and outside the harbour.
“Only two organic chemicals were detected, including an environmental breakdown product of the pesticide DDT and the insect repellent ingredient DEET, but review of scientific literature suggests the observed levels were unlikely to affect fish health.
“Iron was the only metal found at higher levels in barramundi and whiting collected from the Harbour, however no abnormalities due to excessive iron deposits were observed in the livers.
“Tests for a range of other metals, including lead and mercury, showed that levels were either slightly higher in fish samples from outside the harbour or had similar concentrations to fish samples from the harbour.”
DERM Director-General Jim Reeves said there was little change in the concentration of dissolved metals from December 2011 results to sampling carried out in January.
“No metals exceeded water quality guideline trigger values except for dissolved aluminium levels at three of the 19 sites. This was similar to the results of tests carried out in December, and lower than the November measurements,” Mr Reeves said.
“Exceeding trigger values in the Australian and New Zealand Water Quality Guidelines do not necessarily mean that water quality is harmful to marine life. It triggers the need for action, such as follow up sampling or further investigation of sources.
“Turbidity increased at a number of sites, especially Boat Creek, however this is consistent with spring tide currents picking up sediments from the adjacent intertidal flats. Significantly, turbidity levels at Boat Creek were less in December which typifies the natural rise and fall of turbidity levels in some areas within Port Curtis.
“Nutrient concentrations varied across Port Curtis with some sites showing increases and others showing decreases. There were relatively high nitrogen and phosphorus concentrations at Boat Creek in both November and January coinciding with the high turbidity levels.
“Dissolved oxygen levels were similar to levels recorded in December, except for increases in the upper reaches of the Boyne and Calliope estuaries. The pH levels in all waterways continue to be slightly alkaline which is not unusual.
“Water temperature and salinity levels were slightly higher at most sites than in December. This is consistent with a summer period without major rainfall. The heavy rains that occurred in late January producing flooding in the Boyne River came in the weeks after the water quality samples were collected.
“Chlorophyll-a, which measures the extent of algae, decreased at most sites. The measurements were higher in the Boyne River Estuary but lower in the Calliope River Estuary.”
DERM’s monthly water quality sampling is a key component of the Government’s expanded Integrated Aquatic Investigation Program for Gladstone Harbour, which implements the recommendations of the Gladstone Fish Health Scientific Advisory Panel.
As recommended by the panel, the water quality sampling program was expanded this month to include an increased number of sites and additional sediment sampling for dissolved metals and persistent organic pollutants.
Dredging Today Staff, March 2, 2012; Image: westernbasinportdevelopment