Marine Aquaculture Site: Loch Alsh - Sepa
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Marine Aquaculture Site: Loch Alsh
ANNEX 1 : SEA LICE MANAG EMENT AND EFFICACY STATEM ENT
MARINE HARVEST ( SCOTLAND) LIMITED
WRITTEN BY RUTH PATERSON JULY 2018; REVIEWED SEPTEMBER 2018
Registered in Scotland No. 138843 Stob Ban House, Glen Nevis Business Park,
Registered Office, Fort William, PH33 6RX
1st Floor, Admiralty Park
Ruth. Paterson@marineharvest. com
Admiralty Road
Rosyth
Stob Ban House, Glen Nevis Business Park,
FIFE
Fort William, PH33 6RX
KY11 2YW http:// marineharvest. com
2 | 16
Table of Contents
Table of Contents ...........................................................................................................................................2
Table of Figures ..............................................................................................................................................2
1. Introduction ............................................................................................................................................
3
1 Policy and Legislation Framework ........................................................................................................
3
1.1 Code of Good Practice ................................................................................................................... 3
1.2 Aquaculture and Fisheries Scotland Act 2013 ............................................................................. 3
1.3 Current Compliance ...................................................................................................................... 4
2 Historic Sea Lice Challenges .................................................................................................................. 4
2.1 Marine Harvest Response to Rising Sea Lice Numbers ..............................................................5
3 Development of Lice Management Tools ..............................................................................................6
3.1 Cleaner Fish ...................................................................................................................................
6
3.2 Non-Medicinal Lice Treatments ...................................................................................................
7
3.2.1 Hydrolicer Units .......................................................................................................................
7
3.2.2 Thermolicer Units .....................................................................................................................
7
3.2.3 Freshwater Treatments ............................................................................................................
9
3.2.4 Pen Modifications ...................................................................................................................
10
3.3 Medicinal Treatments .................................................................................................................
10
3.4 Good Husbandry Practice ............................................................................................................11
4 Treatment Selection and Hierarchy ....................................................................................................
12
5 Conclusion ............................................................................................................................................12
Appendix 1 Example Treatment Plan: Loch Alsh .......................................................................................
13
6 References ............................................................................................................................................. 16
Table of Figures
Figure 1. Adult Female Lice Levels vs Marine Scotland Thresholds 2016-2018. ................... 4
Figure 2. Average monthly adult female levels 2014-2018. ................................................... 5
Figure 3. Marine Harvest cleaner fish deployment plan 2018-2022. ...................................... 6
Figure 4. Schematic of a thermolicer system used within Marine Harvest.............................. 8
Figure 5. Flusher results from 2016 to 2018 for adult female lice clearance levels. ............... 9
3 | 16
1. Introduction
Effective sea lice management is a critical requirement to protect the health and welfare of
farmed fish and to minimise the risk of potential impacts on wild salmonids. Marine Harvest
Scotland) Ltd. has incrementally introduced a suite of internal policies, targets, and capital
investment programmes1 to significantly improve sea lice management, in parallel with gradual
reduction of medicinal treatments.
The company is now equipped with an increased range and capacity of sea lice management
tools, not previously available up until early 2016. This document summarises these changes,
outlines the general efficacy of each treatment and illustrates how these can be applied in an
integrated manner to effectively manage sea lice issues.
In this document, Marine Harvest sets out its policies and aims on sea lice management and
details the operational approach and resources to target sites to meet regulatory and industry
guideline treatment thresholds for sea lice, but also importantly the stricter operational
intervention thresholds the company apply and aspire to meet. This document outlines how
the investment in sea lice management tools is being applied across Marine Harvest; the
efficacy that is being achieved with these new tools; and the declining levels of parasitic loading
that is now being seen as a result.
1 Policy and Legislation Framework
1.1 Code of Good Practice
In 2006, the Code of Good Practice for Scottish Finfish Aquaculture (CoGP)2 was introduced
covering the production of all types of finfish farmed in Scotland and the good practice stated
within underpins all aspects of fish farming operations ( CoGP, 2003). The National Treatment
Strategy for the Control of Sea Lice on Scottish Salmon Farms was subsequently revised and
incorporated into the CoGP, taking new initiatives on maximising the efficacy of sea lice
treatments and medicines, and minimising sea louse resistance. A primary objective of the
revised strategy is the target of zero adult female lice on farmed fish in the spring period when
wild salmonids are migrating, achieved by coordinated spring treatments, conducted by all
farms within defined management areas that are in their second year of production, or if lice
numbers are above the defined management threshold levels. These levels are as follows:
0.5 adult female lice per fish from February to June to minimise any potential for
interaction with the wild smolt run; and
One adult female per fish from July to January.
1.2 Aquaculture and Fisheries Scotland Act 2013
In 2007 the Scottish Parliament made provisions in relation to fish farms, specifically with
regards to the control of sea lice (amended in 2013) which put into regulatory context minimum
1
In the last 2 years, Marine Harvest has invested over £ 16 million in the acquisition and development of the latest available,
non-medicinal methods of sea lice control. These new non-medicinal treatments, only developed since late 2015 include
Hydrolicer” systems, “ Thermolicer” systems, and new Freshwater treatment systems
http://thecodeofgoodpra
2 http:// thecodeofgoodpractice. co.uk/
ctice.co.uk/
4 | 16
legal standards covering the health and welfare needs of farmed fish, including measures for
the prevention, control and reduction of parasites on fish farms.
In 2017 Marine Scotland significantly updated their guidance and monitoring to ensure that all
sea lice control measures being implemented on Scottish fish farms can be considered as
satisfactory. This new ( 2017) monitoring scheme includes a new mandatory reporting level
where any farm reaching an average of 3.0 adult female lice per fish requires to be reported
to the Fish Health Inspectorate ( FHI). If such a lice level is reached, increased monitoring by
the FHI is implemented and continued until the adult female lice count is reduced to below the
reporting level of 3.0. However, if a farm reaches a higher level, averaging 8.0 adult female
sea lice per fish, FHI requires the creation and implementation of an explicit action plan, agreed
with the FHI to effectively reduce and maintain the average number of adult female lice below
the reporting level of 3.0. These measures can include the requirement to harvest out the
affected fish stocks.
1.3 Current Compliance
The recent investments and advancements in better methods and strategies for controlling sea
lice have resulted in a trend of progressive improvement in compliance rates with Marine
Scotland sea lice reporting and intervention thresholds ( Figure 1).
Figure 1. Adult Female Lice Levels vs Marine Scotland Thresholds 2016-2018.
2 Historic Sea Lice Challenges
The years 2013-2015 and the beginning of 2016 were challenging for the aquaculture sector
as a whole. Elevated summer temperatures accelerated the life cycle of gill parasites and sea
lice resulting in higher levels of parasitic loading to the farmed stock (Murray, 2016). This was
5 | 16
during a period when there was a significantly lower cleaner fish capacity and when non-
medicinal treatment systems were still being developed.
Figure 2. Average monthly adult female levels 2014-2018.
2.1 Marine Harvest Response to Rising Sea Lice Numbers
A successful lice management strategy requires access to a range of effective, unrelated
active ingredients and tools, to maintain efficacy. There are presently five active ingredient
products available in various product formulations for use as sea lice medicines in Scotland;
the bath treatments: cypermethrin, azamethiphos, deltamethrin, and hydrogen peroxide; and
the in-feed treatment emamectin benzoate.
The company invested heavily in improving and developing new tools for better lice
management, resulting in a corresponding improvement in lice numbers. This included the
increased deployment of both existing, and proven preventative measures. These included
non-medical treatments options such as:
The first production versions of the new ‘flusher’ systems (Hydrolicer, Thermolicer);
The newly developed use of freshwater treatments; and
Investment to increase the capacity of biological controllers, such as cleaner fish
Ballan Wrasse, Lumpsuckers).
6 | 16
3 Development of Lice Management Tools
3.1 Cleaner Fish
The term ‘cleaner fish’ refers to fish, typically Ballan Wrasse and Lumpsuckers, that provide a
symbiotic ‘ cleaner’ service to other fish species by the removal of parasites ( Imsland et al.,
2014). The Scottish Salmon industry is increasingly stocking cleanerfish into marine salmon
farms and they have proven effective in reducing sea lice numbers, and significantly reducing
the need for medicinal treatments ( Deady et al., 1995; Leclercq et al., 2014). Currently 100%
of all Lumpsuckers deployed per annum in Marine Harvest sites are of farmed origin; however,
at present only 10% of the Ballan Wrasse used are of farmed origin.
In response to the limited availability of farmed stocks of Ballan Wrasse, Marine Harvest has
also now committed to the development of in-house cleaner fish farming. The company has
invested significant financial and technical resources into the development of several
pioneering cleaner fish hatcheries at locations around the UK. Recently a new recirculation
plant was purchased to produce farmed Ballan Wrasse. This facility will be developed over the
next few years into a state of the art cleaner fish hatchery. The facility will aim to produce
Ballan Wrasse as a sustainable cleaner fish that will then be deployed into the company’s
salmon farms. When fully operational, by 2021, this facility will produce 100% of Ballan Wrasse
demand for Marine Harvest. In the intervening period there will be a steady transition towards
producing cleaner fish stocking requirements from hatchery sources with an annual
corresponding declining impact on sourcing these fish from the wild stocks.
The sector as a whole is in the process of developing knowledge of growing cleaner fish in
hatchery environments. The husbandry methods used to grow, handle and distribute cleaner
fish are evolving with the increased knowledge and expertise within this new area. In the
interim period, company policy states that wild juvenile Ballan Wrasse less than 12cm in length
or mature Ballan Wrasse greater than 22cm in length will not be removed from the wild to
ensure the sustainable continuation of viable breeding wild populations of the species.
Figure 3. Marine Harvest cleaner fish deployment plan 2018-2022.
7 | 16
3.2 Non-Medicinal Lice Treatments
Since late 2015, Marine Harvest Scotland has been developing and investing heavily in the
development of non-medicinal methods of sea lice control. Non-medicinal treatments
developed and adopted since 2015 include hydrolicer systems; thermolicer system and
freshwater treatments. These technologies are still emerging and are constantly being
developed, however to date they have demonstrated high treatment efficacies against lice
infection.
3.2.1 Hydrolicer Units
Hydrolicer systems work by using variable-pressure seawater to dislodge sea lice from the
salmon without any detrimental impact on the fish. The method is benign in that it only uses
seawater and fish are not exposed to physiological stress or deteriorating water quality.
Dislodged sea lice are removed from the used seawater by fine mesh filtration, collected and
disposed of by incineration on land. The first prototype hydrolicer unit in Marine Harvest was
brought into operation in late December 2015.
Given the success of the hydrolicer method, Marine Harvest has invested in developing and
expanding the number of hydrolicer units that it now operates. At present, there are three
operational hydrolicer units, fitted to the decks of workboats, enabling scheduled and
responsive treatments to be undertaken at seawater farm locations. Further development in
vessel technology will see hydrolicer units incorporated into the design of well boats or larger
dedicated service vessels, further optimising system performance.
Marine Harvest currently has the capacity to treat approximately 31,000t in 14 days with
mechanical tools i.e. hydrolicers and thermolicers. This equates to 2300t per day. This capacity
means the company’s complete standing biomass currently held in the sea can be treated in
less than 14 days with non-medicinal treatments.
3.2.2 Thermolicer Units
Thermolicers are an effective and safe option for the mechanical removal of sea lice. Sea lice
have a low tolerance to changes in body temperature ( Costello, 2006; Torrissen et al., 2013),
the system works by exposing the fish to lukewarm water for 30 seconds, which subsequently
dislodges sea lice due to the rapid temperature change. Due to the significant body mass of
the salmon, relative to the diminutive size of the sea lice, there is no measurable change to
body temperature of salmon but sea lice are sufficiently affected to detach from the salmon.
Figure 4 illustrates how the system operates.
8 | 16 Figure 4. Schematic of a thermolicer system used within Marine Harvest. The first thermolicer was brought into operation in 2016. Efficacy on all mobile stages of sea lice has generally been very good and fish rarely show negative signs that can be ascribed to the system itself. Recognising the success of this method, a second thermolicer unit was purchased and brought into action in November 2017. The efficacy of the hydro- and thermolicer systems to date are summarised in Figure 5.
9 | 16
Figure 5. Flusher results from 2016 to 2018 for adult female lice clearance levels.
3.2.3 Freshwater Treatments
Freshwater treatments have been recognised as an effective strategy for both sea lice and
Amoebic Gill Disease (AGD) control. In combination with other available technologies, such as
mechanical and biological control, freshwater treatments expand the available fish welfare
management tools for sea lice infestation and AGD.
Wellboats have been targeted as the optimum solution to deliver freshwater treatment
solutions to site, as this offers an opportunity to control conditions, facilitate fish movements,
and prevent any mixing of freshwater and seawater during treatment. The majority of
treatments are carried out with a holding time of twelve to sixteen hours with lice clearance
efficacy regularly high for all stages of sea lice development.
Sourcing freshwater abstraction sites for direct fill to well boats is an important element in
ensuring the success of this strategy. Currently, the most effective option for freshwater supply
is via abstraction from natural freshwater bodies ( burns or lochs). All abstractions require a
license from SEPA and the relevant planning authority; to ensure that the rate of abstraction
from individual waterbodies is controlled and to ensure good environmental flow standards in
the watercourse, maintaining the ecological quality of the watercourse. The abstracted water
is then pumped or gravity fed by pipe for containment in enclosed tarpaulins within pens held
in seawater, usually located near the abstraction source.
In addition to freshwater abstraction, Marine Harvest has invested in a new wellboat,
specifically designed to undertake freshwater treatments at seawater farms using the process
of desalination. This boat can also, if required, obtain water from a natural freshwater
abstraction sources as highlighted above.
At present, Marine Harvest have brought into operation five active freshwater abstraction
locations and storage pen infrastructure, enabling direct fill of freshwater to wellboats to
facilitate sea lice and AGD treatments. There is currently a fleet of three wellboats in Scotland
10 | 16
capable of carrying out freshwater treatments. Several other freshwater abstraction locations
in strategic locations to Marine Harvest farms have been identified and relevant permissions
are in the process of being secured.
3.2.4 Pen Modifications
Research has shown a negative correlation between the swimming depth of fish, and lice
prevalence and number within the water column ( Bui et al., 2016; Frenzl et al., 2014).
Accordingly, a “deep-strategy” concept has been under development with the aim of keeping
fish away from the higher densities of the infective stages of sea lice in the surface layer for
most parts of the day, while protecting fish when they need to ascend, e.g. to fill the swim
bladder. Such a strategy has the potential to significantly reduce the need for lice treatments,
thereby reducing the risk of resistance and improving general fish welfare. There are various
aspects to this strategy and different combinations are in place across existing farms, with
further research ongoing to optimising effectiveness.
Sea Lice Skirts
The highest concentrations of sea lice are typically found in the upper parts of the water column
and preventing this water from passing through the salmon pens has been found to reduce
salmon lice infestation ( Frenzl et al., 2014; Hevrøy et al., 2003). A lice skirt is a 6m deep
tarpaulin which is placed into the water around a fish pen to a depth of 5m sub surface; 1m of
the tarpaulin is retained above the surface of the sea.
Lice skirts have been widely implemented by Marine Harvest since 2016. The deployment of
tarpaulin skirts has been shown to delay the start of the next “first pen” infection. quality within
pens utilising lice skirts is a subject area of ongoing research by Marine Harvest.
Deep Feeding and Deep Lights
The use of deep feeding equipment that has high capacity and spreads the feed spatially at
depth, promoting deep feeding behaviours by salmon and its efficacy as a lice prevention
measure is presently the subject of developing research internally. Prior research has also
demonstrated that the behaviour of salmon, including swimming depth in sea pens, shows
seasonal variations dependent upon a range of environmental factors including light conditions
Bui et al., 2016; Frenzl et al., 2014; Hevrøy et al., 2003). During periods of high light intensity,
salmon typically swim deeper than in periods of low light intensity where the salmon tend to
swim shallower. Marine Harvest are therefore undertaking further research trials on the
potential for behavioural manipulation of salmon, and the subsequent lice prevalence and the
efficacy against infection by utilising measures such as deep feeding and deep lights.
3.3 Medicinal Treatments
The industry adopts a range of measures to control fish health, including good husbandry and
management, natural feed additives, site fallowing, mechanical tools and biological tools such
as cleaner fish and, where necessary, veterinary medicines.
There are presently five active ingredients available (in various product formulations) for use
as sea lice medicines in Scotland: the bath treatments: cypermethin, azamethiphos,11 | 16
deltamethrin, and hydrogen peroxide; and the in-feed treatment emamectin benzoate. All
medicines are prescribed by the company veterinarian and their use is regulated by the
Veterinary Medicine Directorate ( VMD) as well as SEPA. There are also strict criteria and
procedures for monitoring medicinal residues in farmed salmon under food safety regulations
as is the case with terrestrial farmed animals.
3.4 Good Husbandry Practice
Marine Harvest Scotland’ s goal is to rear healthy fish and maximise the welfare on fish stocks.
Fish are tended to under conditions that satisfy their biological needs for food, clean water and
space, and it is ensured that the fish obtain the necessary nutrients for good health throughout
production. The fish are stocked at densities that balance welfare and enhance performance.
Coordinated fallowing and synchronised production are integral components of Marine
Harvest’s farming practices, which reduce biological risk. Under the supervision of fish health
professionals, Marine Harvest continuously apply good farming practices and high standards
of biosecurity to optimize the health and welfare of stocks. By adhering to stringent veterinary
health plans and recognized fish welfare standards, such as Royal Society for the Prevention
of Cruelty to Animals ( RSPCA), and vaccinating 100% of our fish, we reduce biological and
health risks.
Interventions, such as biological control, medicinal treatments, and thermic/ physical removal
of sea lice are only part of an integrated control strategy and would not be successful without
a firm foundation of good fish welfare, husbandry and other preventative measures which
include fallow periods, single year class sites, regular lice counting, etc.
Fallow Periods
The aim is to deprive sea lice of available hosts through fallow periods, i.e. no farmed
salmonids in a farm area for at least four weeks, is highly effective in re-setting the level of sea
lice, as free-swimming juvenile infective stages will die within one week if they can’t find hosts
Torrissen et al., 2013). Current policy states that each site is fallowed for at least six weeks
between production cycles.
Single year class sites
This is linked to fallow period and requires all sites to be stocked with new smolts within a
defined period which allows all to be harvested out again in time for the agreed fallow. New
smolts should not be introduced to a site that still holds harvest sized fish from the previous
generation.
Regular lice counting on farms
The Code of Good Practice requires farms to collect representative lice data at least once a
week from all stocked farms to monitor and actively manage sea lice levels in their stock
CoGP, 2003). Marine Harvest views this as critical to success and dedicates extensive
resource to gathering this data at an even higher level of resolution (more fish counted, from
more pens) than required by the COGP.12 | 16
Communication between companies
Marine Harvest strongly believes that communication with the Health Teams of neighbouring
farms and companies is important, and has a policy of non competative business transparency
in this regard.
4 Treatment Selection and Hierarchy
The criteria defining treatments selected for a particular site is determined on the basis of a
number of decision criteria. Physical systems, i.e. lice treatment skirts are typically installed
throughout the production cycle. Specific strategic treatments are applied to achieve defined
levels of protection, for example the in-feed treatment emamectin benzoate is frequently
applied at the beginning of the wild smolt migration season to maximum protection against
infection during this sensitive period. Decisions regarding the use of other measures are based
on a series of principals to ensure a diverse range or treatments are applied to ensure
continued treatment efficacy, the type of treatment last applied and level of efficacy achieved,
and the availability and capacity of specific treatment options etc. Given the level of
responsiveness required by a lice treatment plan, a defined treatment strategy is unlikely to be
as effective and could lead to the inefficient or unnecessary use of management tools.
Therefore, an example of a treatment plan for the proposed site is provided in Appendix 1 of
this document.
5 Conclusion
Effective sea lice management is important for the health and welfare of farmed fish, and also
to reduce the risk of fish farms on wild salmonids. The company has invested heavily, and
continues to invest, in the management and advancement of tools and methodologies to
combat the occurrence of sea lice on its farms. Measures implemented include cleaner fish,
hydrolicers, thermolicers and freshwater treatments. These new measures are in parallel with
new internal policies
An example treatment plan for the site is provided illustrating the typical timing, nature and
range of treatments implemented during a production cycle to demonstrate the extent of the
potential tools available to ensure sea lice levels meet internal and external targets.13 | 16
Appendix 1 Example Treatment Plan: Loch Alsh
Ten 120m Circle Pens
2500 tonne Maximum Standing Biomass
Note: The company promotes proactive sealice control, as well as monitoring and intervention as part of a reactive approach. This
document is purely an example of how lice levels could be managed based on the current company budget, experience, and
guidance such as the National Treatment Strategy. The need for intervention, the method used, and the timing is dependent on site
conditions and thus subject to change following the results of regular monitoring. Further resource could be made available in
response to fish health.
Available Treatments Colour Code
Lice Skirts
In-Feed
Bath
Cleaner Fish
Mechanical
Production
Year Calander Cycle Treatment
Quarter Week Week Type
1 1 Lice Skirts/ Cleaner Fish
2 2
3 3
4 4
5 5
6 6
19 Q1 7 7
8 8
9 9
10 10
11 11
12 12
13 13
14 14
15 15
16 16
17 17
18 18
19 19
19 Q2 20 20
21 21 In-feed
22 22
23 23 Cleanerfish
24 24
25 25
26 26
27 27 Bath
28 28
19 Q3 29 29
30 30
31 3114 | 16
32 32
33 33
34 34
35 35
36 36 Mechanical
37 37
38 33
39 34
40 35
41 36
42 37
43 38
44 39
45 40
19 Q4 46 41
47 42
48 43
49 44
50 45
51 46
52 47
53 48
54 49
55 50
56 51
57 52
58 53
20 Q1 59 54
60 55
61 56
62 57
63 58
64 59
65 60 Bath
66 61
67 62
68 63
69 64
70 65
71 66
20 Q2 72 67
73 68 Mechanical
74 69
75 70
76 71
77 72
78 73
79 74
80 75
81 76
82 77 Mechanical
20 Q3
83 78
84 79
85 80
86 81
87 8215 | 16
88 83 Mechanical
89 84
90 85
91 86
92 87
93 88
94 89
95 90
96 91
97 92
20 Q4 98 93
99 94
100 95
101 96
102 97
103 98
104 9916 | 16
6 References
Bui, S., Oppedal, F., Stien, L., Dempster, T., 2016. Sea lice infestation level alters salmon
swimming depth in sea-pens. Aquac. Environ. Interact. 8, 429–435. doi:10.3354/aei00188
CoGP, 2003. Code of Good Practice: Chapter 4 Seawater Lochs.
http://thecodeofgoodpractice. co.uk/chapters/ chapter- 4-seawater- lochs/ 2003.
Costello, M.J., 2006. Ecology of sea lice parasitic on farmed and wild fish. Trends Parasitol.
22, 475–483. doi:10.1016/j.pt.2006.08.006
Deady, S., Varian, S.J.A., Fives, J.M., 1995. The use of cleaner- fish to control sea lice on two
Irish salmon (Salmo salar) farms with particular reference to wrasse behaviour in salmon
pens. Aquaculture 131, 73–90. doi:10.1016/0044-8486(94)00331-H
Frenzl, B., Stien, L.H., Cockerill, D., Oppedal, F., Richards, R.H., Shinn, A.P., Bron, J.E.,
Migaud, H., 2014. Manipulation of farmed Atlantic salmon swimming behaviour through
the adjustment of lighting and feeding regimes as a tool for salmon lice control.
Aquaculture 424–425, 183–188. doi:10.1016/j.aquaculture.2013.12.012
Hevrøy, E.M., Boxaspen, K., Oppedal, F., Taranger, G.L., Holm, J.C., 2003. The effect of
artificial light treatment and depth on the infestation of the sea louse Lepeophtheirus
salmonis on Atlantic salmon ( Salmo salar L.) culture. Aquaculture 220, 1–14.
doi:10.1016/S0044-8486(02)00189-8
Imsland, A.K., Reynolds, P., Eliassen, G., Hangstad, T.A., Foss, A., Vikingstad, E., Elvegård,
T.A., 2014. The use of lumpfish ( Cyclopterus lumpus L.) to control sea lice
Lepeophtheirus salmonis Krøyer) infestations in intensively farmed Atlantic salmon
Salmo salar L.). Aquaculture 424–425, 18–23. doi:10.1016/j.aquaculture. 2013.12.033
Leclercq, E., Davie, A., Migaud, H., 2014. Delousing efficiency of farmed ballan wrasse (Labrus
bergylta) against Lepeophtheirus salmonis infecting Atlantic salmon (Salmo salar) post-
smolts. Pest Manag. Sci. 70, 1274–1282. doi:10.1002/ps.3692
Murray, A.G., 2016. A note on sea lice abundance on farmed Atlantic salmon in Scotland 2011-
2013: Significant regional and seasonal variation. Aquac. Res. 47, 961–968.
doi:10.1111/are.12554
Powell, M.D., Reynolds, P., Kristensen, T., 2015. Freshwater treatment of amoebic gill disease
and sea-lice in seawater salmon production: Considerations of water chemistry and fish
welfare in Norway. Aquaculture 448, 18–28. doi:10.1016/j.aquaculture. 2015.05.027
Torrissen, O., Jones, S., Asche, F., Guttormsen, A., Skilbrei, O.T., Nilsen, F., Horsberg, T.E.,
Jackson, D., 2013. Salmon lice - impact on wild salmonids and salmon aquaculture. J.
Fish Dis. 36, 171–194. doi:10.1111/jfd.12061You can also read
