Gladstone Harbour Fish Health Investigation 2011-2012

Abstract

The Gladstone Harbour Fish Health Investigation occurred in response to public concerns regarding fish health in Gladstone Harbour, which were raised with the former Department of Employment, Economic Development and Innovation (now Department of Agriculture, Fisheries and Forestry (DAFF)) in August 2011. The majority of concerns were regarding skin redness, lesions and eye damage observed on barramundi caught from the Boyne River or within its vicinity. Further reports included unusual skin redness and occasional lesions observed on a range of fish species from Gladstone Harbour (including sharks), as well as an increase in the incidence of shell erosion on mud crabs. The subsequent investigation aimed to determine the cause of the reported issues and specifically to address public concern regarding the potential impact of industrial activity including dredging in Gladstone Harbour. The investigation, conducted by DAFF, was part of a whole-of-government response, which included sediment and water quality testing; and investigation into human health concerns.

The first reports of abnormalities in fish were received months after a major flood event happened in Gladstone from December 2010 until early 2011. The flood event caused a dramatic influx of large barramundi (estimated 30 000), as well as other species from Lake Awoonga into the Boyne River when the Awoonga Dam spilled over. The dam had not spilled over since the 1990s, well before the dam wall was raised in 2002. Many of these fish were injured (some fatally) from the force of the impact when passing over the spillway. It is believed that a smaller number of fish were washed over during a second flood event in early 2012.

The initial response investigated fish with visible abnormalities (e.g. missing scales and redness), and signs of disease to indicate the cause of the observed issues. This early sampling (Phase 1) between August 2011 and February 2012 was based on observations of commercial fishing activity, contracted fish surveys and submissions by members of the public. Over 5000 fish, crustaceans and molluscs were visually assessed during this sampling.

In January 2012, the Independent Gladstone Fish Health Scientific Advisory Panel released a report recommending a structured sampling program to gauge fish health in Gladstone Harbour sites against comparable unaffected sites (reference sites), through time. It also recommended the development of a conceptual model of possible cause-effect relationships to help guide studies and eliminate potential causal factors.

Structured sampling in Gladstone Harbour (Phase 2) was conducted in two major surveys during April–May (Trip 1) and June–July (Trip 2) 2012. These surveys covered 11 sites including two reference sites and focussed on a subset of 10 species. The selected species represented a range of different life cycles (e.g. catadromous and estuarine) and trophic levels (e.g. predatory, omnivorous detritivores and scavengers), and had been reported with a variety of abnormalities. A third targeted survey was conducted in September 2012 to monitor potential seasonal reoccurrence of parasitic infestations in the barramundi from the Boyne River. A total of 3699 fish and crustaceans were visually assessed in the field, with 452 specimens examined by necropsy, and tissues from 120 specimens subjected to histopathology and chemical residue testing.