Optimal treatment regimes from productivity and economic standpoints: The management of suspended mussel lines using high pressure water treatments for the vase tunicate, Ciona intestinalis

The invasive tunicate Ciona intestinalis (L., 1767) had an economic impact on the aquaculture of the blue mussel Mytilus edulis (L., 1758) in Prince Edward Island (PEI) and other areas. This tunicate fouls mussel socks suspended on long lines in the water, increasing the weight of the lines and reducing the weight and number of mussels, decreasing overall productivity and profitability. This study determined the relative effects of high pressure water treatment schedules over a 4 month period on two representative sites located in Murray and Brudenell Rivers on PEI. Results indicated that initiating treatment early in the season (July) and treating another 2 or 3 times on a monthly basis had the greatest effect on reducing tunicate numbers and size and enabling greater mussel productivity and farm profitability. While the most effective treatment may ultimately be site-specific, the two sites in this study support the notion that beginning treatment when tunicates are small is one of the most significant parts of a treatment strategy. The optimal treatment strategy needs to be balanced with the most cost effective regime to maintain or improve the economic potential of a mussel farm. Results show that a treatment regime that includes three or four treatments consistently results in an economic advantage over treating two times. If treating mussel socks only two times, treating them early also shows substantial economic advantage