The potential of integrated open-water mussel (Mytilus planulatus) and Atlantic salmon (Salmo salar) culture in North West Bay, Tasmania
Creators: name: Cheshuk, BW
Publisher: name: University Of Tasmania
Year: 2023

description: Tasmanian blue mussels (Mytilus planulatus) were cultured at four sites in the vicinity of an Atlantic salmon (Salmo salar) farm in North West Bay, Tasmania. The main objective of the study was to evaluate the potential of integrating mussel and salmon culture within a common multi-species marine farm. Filter-feeding bivalves cultured near open fish cages might obtain additional food supplies directly from particulate wastes (excess fish feed and faeces) and indirectly from enhanced phytoplankton production stimulated by dissolved nutrient wastes. Potential benefits of such integration include enhanced bivalve growth, increased productivity of a coastal marine fish farm, and reduced fish farm waste loadings and their associated environmental impacts. Mussels were cultured for fourteen months, suspended from four longlines positioned at increasing distances (70, 100, 500 and 1200 meters) from the Aquatas Pty. Ltd. salmon farm in North West Bay. Mussels were monitored monthly for various growth and biochemical parameters including shell length, whole live weight, meat weights, total biomass, condition index, glycogen content, stable isotope ratios (˜í¬•13C and ˜í¬•15N), reproductive development and survival. Water quality and environmental parameters at each longline site were monitored weekly over the same period. The performance of mussels grown within the fish farm lease (70 m and 100 m from the fish cages) was not appreciably different from that of mussels grown distant to the farm. Mussels spawned twice with no differences in biomass production among sites (P &gt; 0.05). The final sample in May 1996 indicated no site differences for any parameter except for shell length (P &lt; 0.0001) and condition index (P &lt; 0.01). However, site differences were minor, with final mean shell lengths and condition (dry meat weight/internal shell cavity capacity) being within 2.0 mm and 17%, respectively. Similar mussel growth was likely due to similarities in environmental parameters among longline sites, most importantly food quantity and quality (POM, chlorophylla, %POM). Growth of mussels cultured within the fish farm was not enhanced due to several contributing factors: (a) solid waste loadings (feed particles and faeces) from the farm were too diluted to significantly increase particulate food concentrations above ambient levels; (b) phytoplankton production within the farm was not enhanced; (c) mussels may have been cultured too distant to intercept settling particulate wastes emanating from the fish cages; and (d) ambient seston concentrations were above, or near, the pseudofaeces threshold concentration for most of the trial period. Therefore, mussels cultured within the farm site were physiologically limited in securing a significant quantity of additional food. Increased bivalve growth through integration with open-water fish culture may only be achievable in coastal areas where ambient food concentrations are below the pseudofaeces threshold for extended periods, particulate fish farm wastes significantly increase particulate food concentrations above ambient levels, and bivalves are cultured in a suitable position to intercept these waste particles.