title: Effect of timing of count events on estimates of sea lice abundance and interpretation of effectiveness following bath treatments.
abstract: Effectiveness of sea lice bath treatment is often assessed by comparing pre- and post-treatment counts. However, in practice, the post-treatment counting window varies from the day of treatment to several days after treatment. In this study, we assess the effect of post-treatment lag time on sea lice abundance estimates after chemical bath treatment using data from the sea lice data management program (Fish-iTrends) between 2010 and 2014. Data on two life stages, (i) adult female (AF) and (ii) pre-adult and adult male (PAAM), were aggregated at the cage level and log-transformed. Average sea lice counts by post-treatment lag time were computed for AF and PAAM and compared relative to treatment day, using linear mixed models. There were 720 observations (treatment events) that uniquely matched pre- and post-treatment counts from 53 farms. Lag time had a significant effect on the estimated sea lice abundance, which was influenced by season and pre-treatment sea lice levels. During summer, sea lice were at a minimum when counted 1 day post-treatment irrespective of pre-treatment sea lice levels, whereas in the spring and autumn, low levels were observed for PAAM over a longer interval of time, provided the pre-treatment sea lice levels were >5-10.
authors.affiliation: Department of Health Management and Centre for Veterinary Epidemiology Research, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Gautam
authors.affiliation: Department of Health Management and Centre for Veterinary Epidemiology Research, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Vanderstichel
authors.affiliation: Department of Health Management and Centre for Veterinary Epidemiology Research, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, Canada.
authors.forename: A S
authors.initials: AS
authors.lastname: Boerlage
authors.affiliation: Department of Health Management and Centre for Veterinary Epidemiology Research, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, Canada.
authors.forename: C W
authors.initials: CW
authors.lastname: Revie
authors.affiliation: Department of Health Management and Centre for Veterinary Epidemiology Research, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, Canada.
authors.forename: K L
authors.initials: KL
authors.lastname: Hammell
mesh_terms: D000818:Animals; D017756:Aquaculture; D033342:Copepoda / Q000502:physiology*; D004478:Ectoparasitic Infestations / Q000453:epidemiology / Q000469:parasitology / Q000662:veterinary*; D005260:Female; D005393:Fish Diseases / Q000453:epidemiology* / Q000469:parasitology; D008297:Male; D009509:New Brunswick / Q000453:epidemiology; D011156:Population Density; D012474:Salmon
keywords: lag time; post-treatment; sea lice; treatment effect