Evaluation of water salinity effects on the sea lice Lepeophtheirus salmonis found on farmed Atlantic salmon in Muchalat Inlet, British Columbia, Canada

Abstract

The sea louse Lepeophtheirus salmonis is a major ectoparasite of both farmed and wild salmonids that causes substantial economic losses to the salmon industry worldwide. However, in British Columbia (BC) sea lice do not typically represent a significant health threat to farmed salmon. Sea lice patterns on Atlantic salmon farms in BC are not fully understood, but it is believed they are highly influenced by sea water salinity levels, which vary dramatically over the year. The objective of this investigation was to evaluate the effects of changes in water salinity on mobile L. salmonis found in farmed salmonids in the Muchalat Inlet, BC, while controlling for potential confounding factors. Using daily farm-based salinity measurements over a 13-year period, we built different salinity metrics to summarize salinity drops within specific periods of time prior to sea lice sampling events. Our results suggest that reduced salinity negatively impacted mobile sea lice in three different ways: first, a direct effect on mobile lice, lasting no more than 1 day; second, an effect mediated by detrimental impacts on pre-mobile lice stages; and third, an effect possibly associated with reduced fecundity of parents of that lice cohort. These findings confirm the important role of salinity on sea lice population dynamics in BC, and contribute new knowledge which is useful in understanding sea lice patterns and determinants in this region.

Evaluating the spatial range of the effect of synchronized antiparasitic treatments on the abundance of sea lice Caligus rogercresseyi (Boxshall & Bravo, 2000) in Chile

“…Weekly water temperature and salinity during the follow‐up period were included in the model building process, as these factors have been described as strong modulators of C. rogercresseyi 's life cycle in experimental (Bravo, Pozo & Silva, ; González & Carvajal, ) and observational settings (Kristoffersen et al., ; Yatabe, Arriagada, Hamilton‐West & Urcelay, ). Previous research into L. salmonis has found that salinity probably reduces the survival rates of the larval and sessile stages of L. salmonis (Arriagada, Vanderstichel, Stryhn, Milligan & Revie, ; Samsing et al., ; Tucker, Sommerville & Wootten, ). Consequently, in order to tackle these lice stages, we evaluated the effect of water salinity 1 and 2 weeks prior the sea lice assessment.…”

Comparison of Remotely-Sensed Sea Surface Temperature and Salinity Products With in Situ Measurements From British Columbia, Canada

“…Salinity and temperature measurements were taken at wild sites using either YSI R 85 or YSI R 6-series multi-parametric sondes (YSI Incorporated, www.ysi.com). At farm sites, these were measured using an RHS-10ATC refractometer (Huake Instrument Co, Guangdong, China), and an OxyGuard Handy Polaris portable meter (Arriagada et al, 2016). Farm measurements were taken at the surface (<20 cm) and at depths of 1, 5, 10, and 15 m, while wild site measurements were taken at the surface (<20 cm) and at depths of 1 and 5 m. Water temperature and salinity were recorded up to two decimal points in degrees Celsius and parts per thousand (ppt) respectively, daily, for the whole year, for each salmon farm site (when sites were active), at the same location and at approximately the same time each morning.…”

Association between sea lice (Lepeophtheirus salmonis) infestation on Atlantic salmon farms and wild Pacific salmon in Muchalat Inlet, Canada

“…The effects of salinity on the development of L. salmonis and local infestation levels in regions of BC for this parasite have been established 30 , 40 . In line with our study objective, to account for the potential confounding effects of salinity and temperature on the relationship between the overall load of lice from the farms and the prevalence of infestation on wild fish, we included the month fixed-effects as well as the year random effects in our final models.…”

“…Because the farming activity was limited to only one farm between 2004 and 2007, we initiated our study with the 2007 data. More details on sampling and lice counting procedures have been presented elsewhere 30 . For our statistical analyses, the data were aggregated at the farm level and each analytical unit was defined as a unique combination of farm-year-month.…”

“…Chum ( O. Keta ), in Muchalat Inlet provided an ideal setting for conducting our study of the host-parasite dynamics within this aquatic ecosystem. Two studies have been conducted previously by our group in collaboration with partners from the Muchalat Inlet on sea lice infestation and its associated determinants on farmed salmon 30 and wild juvenile salmon 29 , but neither of those studies looked at the potential transmission of sea lice between farmed and wild salmon. In addition, our access to high quality data over the last few years is another advantage that motivated us to conduct the current study.…”