How are the salmon lice (Lepeophtheirus salmonis Krøyer, 1837) in Atlantic salmon farming affected by different control efforts: A case study of an intensive production area with coordinated production cycles and changing delousing practices in 2013–2018

Abstract

The aims of the present study were to describe the salmon lice (Lepeophtheirus salmonis Krøyer, 1837) situation in an intensive salmon production area in mid‐Norway and to consider implications of changing practices of how salmon lice infestation can be controlled. The results in this study suggest that there are steps that can be carried out to keep salmon lice under control even during years when the temperature facilitates a quick salmon lice development. The present work indicates that the use of cleaner fish can delay the time it takes adult female lice to reach 0.1 per salmon in the beginning of a production cycle. It suggests that the timing of cleaner fish deployment into salmon cages can influence its effectiveness in controlling salmon lice. It also gives caution to letting salmon lice develop unchecked, even at levels far below the current lice limit, because of the difficulties to control salmon lice when the external infection pressure is too high. This study took place during a rapid change in delousing methods, in an area with coordinated salmon production. Despite its exploratory nature, this study offers insights into the salmon lice fluctuations in relation to efforts aimed at controlling it.

Planktonic and Parasitic Sea Lice Abundance on Three Commercial Salmon Farms in Norway Throughout a Production Cycle

“…One of the localities had an early increase in the number of C. elongatus after salmon deployment; this first increase was slow, followed by a steeper increase 7 weeks later. The same pattern of variation was apparent also for the total number of L. salmonis in the area (Jevne and Reitan, 2019). A slow increase was followed by a steeper increase after the appearance of adult female salmon lice on the salmon.…”

“…In 2017, the measured densities of planktonic sea lice at the NoskirtA locality did not correlate with the predicted nauplius production for the cages they were sampled from, but the average density correlated moderately with the predicted nauplius production of the management area, whereas the mean abundance correlated moderately with the locality's own predicted nauplius production. The NoskirtA locality was located closer to the center of the management zone than the other two localities, which were both located further upstream in the main water current (Jevne and Reitan, 2019). NoskirtA might therefore have been more exposed to planktonic sea lice from the surrounding localities.…”

“…At all localities in this study, sea lice were counted by the company's employees on 20 salmon per cage. The total number of attached salmon lice for the study area was based on data described in Jevne and Reitan (2019).…”

“…Salmon lice are often a more prominent problem for the farmed salmon during the second year of the production cycle (Heuch et al, 2003;Jevne and Reitan, 2019). Among the methods of sea lice control, salmon farming areas in Norway are regulated by means of a coordinated fallowing period at the end of the production cycle.…”

Salmon Louse (Lepeophtheirus salmonis (Krøyer)) Control Methods and Efficacy in Atlantic Salmon (Salmo salar (Linnaeus)) Aquaculture: A Literature Review

“…The efficacy of a chemical treatment is lessened at high fish densities, with high intensities of treatments, and by the development of resistance to treatments by lice over time [12]. Increased fish density leads to a higher host availability, which can result in a higher parasite abundance [6,[13][14][15]. Concerns have been raised about potential negative impacts of chemical treatments on farmed fish and non-target species that may occur in the area close to the aquaculture facilities [16].…”