Horizontal and vertical distribution of sea lice larvae (Lepeophtheirus salmonis) in and around salmon farms in the Bay of Fundy, Canada (original) (raw)
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Scientific reports, 2018
Growth in salmon aquaculture over the past two decades has raised concerns regarding the potential impacts of the industry on neighboring ecosystems and wild fish productivity. Despite limited evidence, sea lice have been identified as a major cause for the decline in some wild Pacific salmon populations on the west coast of Canada. We used sea lice count and management data from farmed and wild salmon, collected over 10 years (2007-2016) in the Muchalat Inlet region of Canada, to evaluate the association between sea lice recorded on salmon farms with the infestation levels on wild out-migrating Chum salmon. Our analyses indicated a significant positive association between the sea lice abundance on farms and the likelihood that wild fish would be infested. However, increased abundance of lice on farms was not significantly associated with the levels of infestation observed on the wild salmon. Our results suggest that Atlantic salmon farms may be an important source for the introduct...
Reviews in Fisheries Science, 2006
Contrary to several recent studies, a review (Brooks, 2005) of sea lice (Lepeophtheirus salmonis) interactions between wild and farm salmon in the Broughton Archipelago, British Columbia, Canada, concluded that there is little potential for sea lice transmission from farm to wild salmon. In this rebuttal, we show that this conclusion was based on a flawed interpretation of how salinity affects louse development, a misunderstanding of how the timing of salinity changes corresponds to the timing of the juvenile salmon migration, models of larval dispersion that overestimate the transport of louse larvae, and a selective and misleading assessment of the literature. We analyze and extend the current models of larval dispersion and demonstrate the (perhaps counter-intuitive) result that sustained high abundances of infectious larvae should be expected near liceinfested salmon farms. We also highlight important studies overlooked in Brooks (2005) and clarify some misinterpretations. Counter to the conclusions in Brooks (2005), the modeling and empirical work to date on sea lice interactions between wild and farm salmon are consistent and point to a strong association between salmon farming and recurrent infestations of wild juvenile salmon in the Broughton Archipelago.
Aquaculture
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.
Frontiers in Marine Science, 2021
The present article reports the densities of planktonic sea lice (Lepeophtheirus salmonis and Caligus elongatus) in three Atlantic salmon (Salmo salar) localities, and the relationship between the abundance of adult sea lice on the salmon and the densities of planktonic sea lice stages, during a complete production cycle followed by a fallowing period. Samples were taken downstream inside and immediately outside of cages, at one locality with lice skirts and two localities without lice skirts. There were no differences in densities of planktonic sea lice in samples taken from the inside or the outside of cages for any of the localities. However, the proportion-non-zero of planktonic sea lice samples taken from inside the cage was higher during months with a temperature above 9 • C (mean abundance: 0.40-2.5 individuals m −3) than months with temperature below 9 • C (mean abundance: 0.02-0.21 individuals m −3 , odds ratio of the proportion-non-zero: p < 0.01). Densities of planktonic sea lice correlated most strongly with temperature in the first year (τ = 0.44-0.57, p < 0.05). A significant correlation between the number of adult female lice on salmon and average density of plankton sea lice was found in the locality with lice skirts during the second year (τ = 0.43 inside cages, τ = 0.58 outside cages, both p values < 0.05). Background levels of planktonic sea lice in the succeeding fallowing period showed neither L. salmonis nor C. elongatus planktonic sea lice, suggesting that there was successful reduction of the densities of planktonic sea lice for this area during the fallowing period.
ICES Journal of Marine Science, 2018
Current sea louse models attempt to estimate louse burdens on wild and cultured salmon by predicting the production and distribution of lice larvae and estimating the risk of transmission. While physical characteristics of water bodies and weather can be accurately modelled, many aspects of sea lice biology require further parameterization. The aims of this review are (i) to describe current knowledge regarding the production, mortality, and infectivity of planktonic sea lice larvae and (ii) to identify gaps in knowledge and suggest research approaches to filling them. Several major gaps are identified, and those likely to have the greatest impact on infection levels are (i) egg production, viability and hatching success, (ii) predation in plankton and (iii) copepodid infectivity profiles. A key problem identified in current parameter estimates is that they originate from a number of sources and have been determined using a variety of experimental approaches. This is a barrier to th...
North American Journal of Fisheries Management, 2007
Recent infestations of sea lice Lepeophtheirus salmonis on wild juvenile pink salmon Oncorhynchus gorbuscha and subsequent declines in the number of returning adult pink salmon have raised concern for the health of wild fish relative to salmon farming activities in the Broughton Archipelago, British Columbia. I used available (but limited) industry data to estimate sea louse egg production from Atlantic salmon Salmo salar farmed by Stolt Sea Farm (now Marine Harvest Canada, Inc., Campbell River, British Columbia) in 2003 and 2004. The 12 active farms contained between 1 and 5 million Atlantic salmon during the 2 years and about 800,000 fewer mature salmon at the start of 2003 than in 2004. Sea louse egg production peaked during winter-spring in both years prior to the seaward migration period of the area's small and vulnerable juvenile pink salmon and chum salmon O. keta. Marine Harvest Canada salmon hosted over 6 million gravid sea lice that produced 1.6 3 10 9 eggs during 2 weeks in the winter of 2003-2004. Only half as many eggs were produced from the fewer hosts present during this period in 2003. Sea lice on farmed fish were further reduced to near zero each year through multiple uses of emamectin benzoate (Slice). Fewer farmed Atlantic salmon and sea lice in 2003 coincided with lower abundance and prevalence of L. salmonis on juvenile pink salmon and chum salmon near farms. A recent agreement between industry and conservationists may help improve data quality, our understanding of the dynamics sea louse-salmon interactions, and our chances of conserving wild salmon.
ICES Journal of Marine Science, 2010
Morton, A., Routledge, R., McConnell, A., and Krkošek, M. 2011. Sea lice dispersion and salmon survival in relation to salmon farm activity in the Broughton Archipelago. – ICES Journal of Marine Science, 68: 144–156. The risk of salmon lice (Lepeophtheirus salmonis) transmission to wild juvenile Pacific salmon has spurred management change to reduce lice on salmon farms. We studied the abundance of planktonic lice preceding the juvenile salmon outmigration as well as the abundance of lice on juvenile pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon in two distinct migration routes, one containing only fallow farms and the other active farms that applied a parasiticide. Results indicate that fallowing reduces the abundance and flattens the spatial distribution of lice relative to that expected in areas without farms. Active farms remained the primary source of lice, but transmission was reduced 100-fold relative to previous epizootics in the study area. On the migrat...
A method of estimating in situ salmon louse nauplii production at fish farms
Aquaculture Environment Interactions, 2016
Abundance and depth distribution of planktonic sea lice were investigated in relation to hydrodynamics and diurnal solar insolation at a salmon farm in Sundalagið, Faroe Islands. Plankton surveys were conducted by surface tows with a plankton net around the farm and by using a plankton pump at 1, 4 and 6 m depth in a fish cage. The entire sample content was investigated under a stereomicroscope and sea lice were identified. Sea lice of the species Lepeophtheirus salmonis and Caligus elongatus were present at the farm. Nauplii dominated the planktonic stages (> 95%) while copepodids were absent from most samples. The highest observed copepodid density was 0.3 ind. m −3 , which is within the range found in open water. No diurnal vertical distribution pattern was observed for salmon lice nauplii in the net cages, which were most abundant in the top meter of the water column, and density decreased with depth. At 1 m depth, nauplii density was inversely proportional to the current speed at the same depth. From this relation, and the abundance of adult female sea lice on the farmed fish, the in situ nauplii production was calculated to be within 26−68 nauplii female −1 d −1. The lower end of this range is similar to production rates suggested by laboratory studies at similar temperatures (7.8°C).