Sea lice infestation levels decrease with deeper ‘snorkel’ barriers in Atlantic salmon sea‐cages

Abstract

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.

Surface environment modification in Atlantic salmon sea-cages: effects on amoebic gill disease, salmon lice, growth and welfare

“…Fish welfare indicators and weights were similar between snorkel and standard cages, including where snorkels were filled with freshwater, confirming conclusions reached in previous snorkel cage investigations that use of this technology does not affect fish welfare (Oppedal et al 2017. Snout damage, likely due to collisions with net roof and snorkel structures, has been observed in one research scale snorkel cage study (Stien et al 2016) but we did not observe this negative effect here.…”

“…While harvest-sized salmon have been found to position themselves almost exclusively below 4 m deep SW snorkels in identical cages in autumn (Stien et al 2016), periodic post-smolt presence inside 4 to 16 m deep SW snorkels, inferred from low oxygen conditions, was detected by Oppedal et al (2017). Therefore, greater fish residency inside SW snorkels may contribute to lice reduction effects typically seen in this cage type (see Oppedal et al 2017). More work is needed to reveal differences in depth distribution of Atlantic salmon among standard, SW and FW snorkel cage types.…”

“…The snorkel allows salmon to swim up and gulp air at the surface to replenish their open swim bladder for buoyancy regulation (Fahlén 1971. Snorkel cages can reduce salmon lice infestations relative to standard cages at research-and commercial scales (Stien et al 2016, with their effectiveness increasing with increased depth of the snorkel (Oppedal et al 2017). AGD may also be treated using this technology by adding a freshwater surface layer inside a tarpaulined lined tube in the snorkel space (Wright et al 2017) that would remove P. perurans from gills if the fish expose themselves sufficiently to freshwater (Parsons et al 2001, Clark et al 2003, Roberts & Powell 2003.…”

Snorkel technology to reduce sea lice infestations: efficacy depends on salinity at the farm site, but snorkels have minimal effects on salmon production and welfare

“…School swimming distance from the halocline was also found to be an important factor of susceptibility in commercial cages, whereby peaks of infestation in control cages were estimated to have occurred when the school was swimming within 5 m of the halocline (Bui et al 2018). This relationship between host exposure to surface waters and susceptibility to infestation is further supported by the results of Oppedal et al (2017), where infestation rates decreased exponentially with increasing barrier depth. Studies that have used depth-based pre- Frequency (%) 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 10-12 Snorkel Control Snorkel base Fig.…”

“…Little or no adverse effects on fish mortality and welfare were detected. Oppedal et al (2017) tested how varying snorkel depths affected lice infestation levels, and found that as snorkel depth increased (0, 4, 8, 12, and 16 m), lice infestations decreased exponentially. Growth, condition, mortality, swimming speeds, and key welfare indices were similar for all snorkel depths .…”