The Ecology of Sea Lice in Cobscook Bay: Understanding the Interactions Between Wild and Farmed Hosts

Sea lice (Lepeophtheirus salmonis) initially infect stocked farmed salmon from sources external to the farm. Once on a farm the lice are able to multiple and can reinfect both wild or farmed fish creating a series of interactions between the parasite and both farmed and wild hosts. Wild fish surveys, sentinel cage deployments and larval transport models are being used to better understand the interactions occurring between this parasite and it farmed and wild hosts. This talk will focus on the results of nearly two years of sentinel cage work. Preliminary results indicate an increasing presence of infection through the late summer and fall with warming water temperatures. Contrary to studies in Europe that observed a cohort of pioneering pre-adults in the spring; the infectious pressure in Cobscook Bay was almost exclusively the infective copepodid stage. The overall risk and intensity of infection observed during the out-migrating smolt window was at levels representative of a sub clinical infection with no physiological impact on the fish. Larval transport models are currently being used to examine potential mechanisms to explain high infectious pressures observed distant to active salmon farms.