Master of Environmental Science (Hons.)
School of Earth and Environmental Sciences
Barker, David, Impacts of marine fish farming with sea cages in Botany Bay, Master of Environmental Science (Hons.) thesis, School of Earth and Environmental Sciences, University of Wollongong, 2008. http://ro.uow.edu.au/theses/2567
Environmental impacts of a fish farm utilising sea cages, located in Botany Bay (NSW) have been assessed prior to and during commercial farming on the site. Sampling criteria and methods were devised to observe possible changes in bottom sediments resulting from fish wastes and possible increases in zinc resulting from placement of two zinc coated wire sea cages on the fish farm. Specifically, sediments from fish farm cage sites within the study site and from seven control locations within Botany Bay were analysed for sediment Total Phosphorus (TP), Total Organic Carbon (TOC) and Zinc (Zn). Sediment samples were also collected and archived for future benthic invertebrate analyses, if required.
Concentrations of sediment TP and TOC taken beneath the fish farm site displayed high spatial and temporal variability but were not significantly different from concentrations taken from control sites. These concentrations were comparable with available data for sediments at other sites within the Sydney Region. Concentrations of TP and TOC beneath sea cages did not significantly increase throughout the period of this study, indicating that fish farming activities had no detectable impact on sediment nutrients. Concentrations of Zn in the surficial sediments in Botany Bay ranged between 2.58 and 282.87 mg/kg and also fluctuated spatially and temporarily. Observed concentrations of Zn beneath sea cages were also well within the range of Zn concentrations sampled throughout Botany Bay. However, and most importantly, concentrations of zinc in surficial sediments under zinc cages did not increase significantly compared to those from control sites. In addition, further investigations were performed to assess possible impacts of zinc coated wire sea cages on Zn levels in the water column and in the farmed fish. Zinc coating on cage netting is used to reduce the accumulation of biofouling organisms.
These results indicated that no significant increases of Zn could be detected in the water column as a result of the placement of the cages on the farm site. Fish (Pagrus auratus) grown within the coated wire sea cage had no noticeable increases in Zn concentrations. The degree of fouling by algae and invertebrates on zinc coated wire was substantially less than that occurring on the “soft” netting currently used by the local aquaculture industry. Overall, no significant impacts from sea cage culture of fish, in terms of sediment TP, TOC, and Zn were found. In addition, zinc coated cages were found to offer considerable advantage in lower rates of marine fouling when compared to material currently used for sea cage netting.