The environmental impacts of land based abolone aquaculture
Creators: name: Ho, J
Publisher: name: University Of Tasmania
Year: 2023

description: This study of land based abalone farming was conducted to investigate the industry's environmental impact and long-term sustainability. There is a paucity of information surrounding the environmental impacts of land based abalone farming despite the increase in the growth of the industry. Information which forms the basis of abalone farm environmental management and monitoring was developed as part of this project. This information is likely to provide a great deal of perspective to all existing and planned Australian abalone farms. Three preliminary experiments were conducted to determine how nutrients were being produced within the abalone farm and how they were varying on a diurnal scale. ; Production ofnutrients is clearly related to the formulated feed, however two possible means of nutrient production were deemed likely. Firstly from the formulated feed leaching or secondly from the degradation of the waste produced on farm. Finally a experiment was conducted to determine the pattern in nutrients exiting the abalone farm's effluent pipe. The nutrient stability of a commercially available formulated feed was assessed. This is of importance as on most Australian abalone farms there is usually a delay between the time the formulated feed enters the abalone culture tanks, and the time of consumption by the abalone. This leads us to believe that there may be nutrients from the formulated feed. The formulated feed leaching appears to be significant in terms of phosphorus (30% of total P content), whilst it appears to be relatively insignificant in terms of all other measured components. This research indicates that there may be a need for further research into the binding of phosphorus in Adams and Amos formulated feed. An examination of the tank waste was conducted to examine if the waste within the abalone culture tanks was a major source of dissolved nutrients that are produced as the waste degrades. Results show that approximately 50% of the C,N,P and organics of the formulated feed was collected in the abalone culture tank waste. Further the settlement pond waste contained approximately 30% of the C,N,P and organics of the formulated feed. This equates to approximately 40- 50% of the abalone tank waste nutrients (i.e. particulate waste) being degraded and remineralised as dissolved nutrients. The temporal variation in nutrient export for a single farm was characterised on a diurnal basis. Maximum concentrations of ammonium and phosphate were recorded at approximately sunrise at the farm outflow on the day of sampling. Therefore the time of day that water sampling takes place is important in the accurate assessment of environmental impact and may explain some of the variability in current monitoring program data sets. Results indicate that of the nutrients measured from a 20 tonne abalone farm, dissolved nitrogen and phosphorus were predominantly exported with exports of, up to, 1000g and 280g per day respectively. The source of these nutrients is the formulated feed. Daily feed rate can predict dissolved nitrogen and phosphate loads exported from the farm (P&lt;0.05, r2 = 0.98 and 0.42 for Nand P, respectively). The relationship between daily feed rate and nutrient export was found to hold at three abalone farms around Tasmania (P&lt;0.05, r2 = 0.71 for Nand r2 = 0.62 for P). These relationships can assist in the environmental management of the abalone industry and provide a consistent basis to judge the impact of abalone farming relative to other sources of nutrient inputs into our coastal environment. This study showed a 10-50 fold increase in biomass of nutrient scavenging seaweeds in the intertidal region in the vicinity of the abalone farm's discharge point. This was relative to both control sites and the discharge site prior to the commencement ofthe effluent discharge. Despite this the farm associated seaweed proliferation is unlikely to occur beyond 50 metres from point of discharge (i.e. at the end-of-pipe). Grazing and particulate feeding intertidal faunal communities were highly variable in time and space making it impossible to detect any effects of the farm's discharge. In the subtidal zone, there was no evidence of an impact on the macroalgal canopy assemblages within 50m of the end-of-pipe. The importance of solid separation devices was also highlighted in this study. Output ofparticulates from farms without Solid Separation Devices (SSD's) is likely to be significantly greater than farms with SSD's (i.e. approximately 30-50% of feed input is lost as particulate waste). Relative to farm inflow waters, Abalone Farms Australia (AFA) did not increase particulate loads into the marine environment (measured by weight); however, even with farms with SSD's, the composition of the particulates in the discharge is likely to change. For example, AFA the discharged particulates had a slightly greater (i.e. 3% greater) organic content relative to intake particulates. This study also showed that effluent nitrogen loads may be reduced by an average of 34% by a novel seaweed raft system held within the tanks. The seaweed raft system not only provided shade but most importantly a nutritious source of supplemental feed for the abalone. The present study intensively examined a single farm, and extensively examined a number of farms to gain a perspective on the environmental impact of the Tasmanian abalone industry relative to other industries that discharge nutrients into the marine environment. The study found that the entire Tasmanian abalone industry as at 2005 was likely to have little more impact than a small town of 600 people's sewage treatment plant (based on total nitrogen discharge). Additionally detailed characterization of abalone farm effluent and the subsequent environmental impacts of that effluent was determined to be negligible for AFA at current production rates (i.e. 20 tonnes of abalone biomass).