Linking physiology, nutrition and environment research to potential impacts of climate change: case-study on Tasmanian Atlantic salmon aquaculture

Atlantic salmon (Salmo salar) is Australia’s largest and most valuable farmed seafood and makes a significant contribution to the rural economy in the state of Tasmania. It is based around transfer from freshwater hatcheries to marine cage farms and, although it accounts for a small part of global salmon production, it is noteworthy for several reasons. Industry is innovative and has developed many technological solutions. There is also a highly active research community which has collaborated widely with industry and other stake holders across ecosystem effects, genetics, health, nutrition, physiology and reproduction. Of particular interest is the relative closeness of Tasmania to the equator which, along with local conditions, means that average water temperatures sometimes approach the upper thermal limits for salmon production. Historically, high water temperatures have been advantageous in promoting high growth, the industry is now managing for potential impacts of climate change. With increasing water temperature metabolic rate increases and dissolved oxygen (DO) decreases so that salmon are more likely to experience hypoxic conditions. Salmon have been considered hypoxia sensitive, however some Tasmanian salmon are able to regulate their metabolic rate and show a level of robustness to their environment. Furthermore, salmon perform optimally over a wide temperature range and maintain high levels of growth performance outside the optimum temperature range. Protein, lipid and mineral nutrition under sub-optimum conditions will be discussed. For example, sub-optimum temperature and DO impacted increased protein and energy requirements. Increasing water temperatures also influences the interaction between aquaculture operations and the environment. Changes in feeds and in husbandry practices such as feeding and stocking regimes will affect the overall nature of the environmental impact, whilst broader ecosystem processes (e.g. seasonal nutrient inputs, current regimes, biogenic processes in the sediment and water column) will be influenced by climate change and may in turn affect the system’s capacity of to assimilate nutrients, both at a local and a system wide scale. Whilst limiting environmental conditions test respiratory physiology, adequacy of nutrient supply and growth, Atlantic salmon have robust physiological systems for maintaining efficient growth.