title: Sea lice infestation levels decrease with deeper 'snorkel' barriers in Atlantic salmon sea-cages.
abstract: BACKGROUND
  Salmon lice (Lepeophtheirus salmonis) are the most important parasites of farmed salmon. Infective larvae position themselves in the upper part of the water column to increase encounter probabilities with potential hosts. Previous studies have shown that a 'snorkel' sea-cage technology protects salmon from infection in surface waters. We tested whether deep snorkels would more effectively reduce lice infestation than shallow snorkels and still uphold adequate conditions for the fish. Five sea-cages (12 m × 12 m) each holding approximately 3000 Atlantic salmon (Salmo salar) (53 ± 10 g) were fitted with snorkels that gave protection from infection for 0, 4, 8, 12 or 16 m. We tested whether reductions in the settlement of new salmon lice copepodids were consistent among four separate infection periods.
  
  
  RESULTS
  Lice infestation decreased exponentially with depth in all time periods. Infection levels in shallow snorkels (0 and 4 m) were consistently 4-10 times higher than those in deep snorkels (12 and 16 m). Key welfare and production performance indices were similar across all snorkel depths.
  
  
  CONCLUSIONS
  Deeper snorkels dramatically and consistently reduced infection levels of salmon lice compared with shallow snorkels, without consequences for fish welfare and production performance. Therefore, reducing salmon sea lice encounters using a depth-based barrier is a powerful management tool for salmon farming. © 2017 Society of Chemical Industry.
authors.affiliation: Institute of Marine Research, Matredal, Norway.
authors.forename: Frode
authors.initials: F
authors.lastname: Oppedal
authors.affiliation: Sustainable Aquaculture Laboratory - Temperate and Tropical (SALTT), School of Biosciences, University of Melbourne, Victoria, Australia.
authors.forename: Francisca
authors.initials: F
authors.lastname: Samsing
authors.affiliation: Institute of Marine Research, Matredal, Norway.|Sustainable Aquaculture Laboratory - Temperate and Tropical (SALTT), School of Biosciences, University of Melbourne, Victoria, Australia.
authors.forename: Tim
authors.initials: T
authors.lastname: Dempster
authors.affiliation: Institute of Marine Research, Matredal, Norway.|Sustainable Aquaculture Laboratory - Temperate and Tropical (SALTT), School of Biosciences, University of Melbourne, Victoria, Australia.
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Wright
authors.affiliation: Institute of Marine Research, Matredal, Norway.|Sustainable Aquaculture Laboratory - Temperate and Tropical (SALTT), School of Biosciences, University of Melbourne, Victoria, Australia.
authors.forename: Samantha
authors.initials: S
authors.lastname: Bui
authors.affiliation: Institute of Marine Research, Matredal, Norway.
authors.forename: Lars H
authors.initials: LH
authors.lastname: Stien
mesh_terms: D000818:Animals; D001681:Biological Assay; D004777:Environment; D005398:Fisheries; D010373:Lice Infestations; D020317:Salmo salar / Q000254:growth & development / Q000469:parasitology*
keywords: Lepeophtheirus salmonis; Salmo salar; fish behaviour; parasite management; production parameters; sustainable farming