Assessment of Sea Lice Infestations on Wild Fishes of Cobscook Bay

Sea lice are ectoparasitic copepods on fishes and can negatively impact aquaculture operations. Little work on sea lice, specifically Lepeophtheirus salmonis and Caligus elongatus, has occurred in the northwest Atlantic. This project characterized sea lice infestations on wild fishes in Cobscook Bay during 2012. Trawling, seine netting, and fyke netting occurred from March to November. Netting sites were selected to sample the bay’s three regions: Outer, Central, and Inner Bay. Visual examinations of fish were used to identify wild hosts and characterize sea lice life stage abundances, attachment locations, and infection prevalence and intensity. DNA sequencing was used to identify sea lice species. Caligus elongatus was the only identified sea lice species, and was found on 12 fish species. Threespine sticklebacks (Gasterosteus aculeatus), blackspotted sticklebacks (Gasterosteus wheatlandi), and winter flounder (Pseudopleuronectes americanus) were prominent hosts with the most infestations (n = 204, n = 32, n = 9). Over 95% of sea lice were in the non-motile chalimus stages, which were predominantly attached to the fish fins. Infection intensity and prevalence on threespine sticklebacks varied significantly between months, reaching maximal values during June. Infection prevalence on threespine and blackspotted sticklebacks differed spatially, with lower levels in Inner Bay than in Central and Outer Bay. Infection prevalence and intensity differed among threespine sticklebacks (12.26%), blackspotted sticklebacks (1.98%), and winter flounder (2.07%), indicating differences in host suitability and importance. These results establish a baseline for sea lice dynamics in Cobscook Bay and inform future sea lice surveys.