Gladstone Fish Health Investigation 2011 - 2012 - Western Basin ...

Executive summaryThe Gladstone Harbour Fish Health Investigation occurred in response to public concernsregarding fish health in Gladstone Harbour, which were raised with the former Department ofEmployment, Economic Development and Innovation (now Department of Agriculture,Fisheries and Forestry (DAFF)) in August 2011. The majority of concerns were regardingskin redness, lesions and eye damage observed on barramundi caught from the Boyne Riveror within its vicinity. Further reports included unusual skin redness and occasional lesionsobserved on a range of fish species from Gladstone Harbour (including sharks), as well asan increase in the incidence of shell erosion on mud crabs. The subsequent investigationaimed to determine the cause of the reported issues and specifically to address publicconcern regarding the potential impact of industrial activity including dredging in GladstoneHarbour. The investigation, conducted by DAFF, was part of a whole-of-governmentresponse, which included sediment and water quality testing; and investigation into humanhealth concerns.The first reports of abnormalities in fish were received months after a major flood eventhappened in Gladstone from December 2010 until early 2011. The flood event caused adramatic influx of large barramundi (estimated 30 000), as well as other species from LakeAwoonga into the Boyne River when the Awoonga Dam spilled over. The dam had not spilledover since the 1990s, well before the dam wall was raised in 2002. Many of these fish wereinjured (some fatally) from the force of the impact when passing over the spillway. It isbelieved that a smaller number of fish were washed over during a second flood event in early2012.The initial response investigated fish with visible abnormalities (e.g. missing scales andredness), and signs of disease to indicate the cause of the observed issues. This earlysampling (Phase 1) between August 2011 and February 2012 was based on observations ofcommercial fishing activity, contracted fish surveys and submissions by members of thepublic. Over 5000 fish, crustaceans and molluscs were visually assessed during thissampling.In January 2012, the Independent Gladstone Fish Health Scientific Advisory Panel releaseda report recommending a structured sampling program to gauge fish health in GladstoneHarbour sites against comparable unaffected sites (reference sites), through time. It alsorecommended the development of a conceptual model of possible cause-effect relationshipsto help guide studies and eliminate potential causal factors.Structured sampling in Gladstone Harbour (Phase 2) was conducted in two major surveysduring April–May (Trip 1) and June–July (Trip 2) 2012. These surveys covered 11 sitesincluding two reference sites and focussed on a subset of 10 species. The selected speciesrepresented a range of different life cycles (e.g. catadromous and estuarine) and trophiclevels (e.g. predatory, omnivorous detritivores and scavengers), and had been reported witha variety of abnormalities. A third targeted survey was conducted in September 2012 tomonitor potential seasonal reoccurrence of parasitic infestations in the barramundi from theBoyne River. A total of 3699 fish and crustaceans were visually assessed in the field, with452 specimens examined by necropsy, and tissues from 120 specimens subjected tohistopathology and chemical residue testing.5