Challenges

Salmon and trout farming entails a relatively higher level of host density compared to in the wild. Infection pressure of wild salmon stocks with sea lice from farmed salmon is one of the main challenges in terms of environmentally sustainable aquaculture.

Due to the host density in farming, Lerøy attempts to keep average numbers of mature female sea lice as low as possible throughout production. Controlling sea lice levels entails higher costs and have the highest priority in Lerøy.

Impacts 

Salmon lice live naturally in the sea and will be able to use our fish in aquaculture as host animals. It is important for Lerøy that we monitor the level of lice in the sea and on fish when the fish is under production. Undesirable quantities of lice will increase the risk that possibly escaped fish from our farms, and smolts that are migrating from the river and passes our farms to the sea, may be attacked by lice. If the lice surcharge becomes too high on our fish, it may exceed the limit values in Norwegian regulations and lead to increased costs for the company, fines, downgrading of fish, reduced fish welfare and, in worse case, fish mortality. Lice infestation on wild smolt could have a negative impact on this species.

Our ambitions in this area

The Group´s efforts to control salmon lice follow the principles of an IPM strategy to control salmon lice and keep the numbers at a low level in the long term. The overall goal is to reduce any negative impact on the environment and the need for active interventions.

The overall principles underlying this control strategy includes establishing acceptable levels (see details in Policy), preventive measures (as structural measures relating to use of locality, coordinated operations over larger geographical areas, zone collaboration, fallow periods in between production cycles, smolt quality and smolt weight as measures to reduce period of exposure, use of various types of physical barriers, (e.g. skirts), monitoring, biological control (i.e. cleaner fish) and active interventions.

We work to minimise levels of adult female lice per fish as close to zero as possible.

How we work in the area

We use targeted measures to reduce the number of lice by reducing exposure in the sea. To do so, we produce larger smolt using RAS technology so we can have shorter production periods in the sea. 

Additionally, to counter the burden of sea lice and its effect on fish 
health and welfare, Lerøy is implementing 
shielding technology at selected sites in Lerøy Midt 
and Lerøy Sjøtroll, as well as deploying optical 
delousing equipment in Lerøy Aurora.  While semi-closed solutions are employed at protected sites, submerged cages are 
rolled out at more exposed sites at greater depths. 
Semi-closed solutions have solid barriers in the form 
of steel skirts and/or impermeable tarpaulins 
physically separating the inside of the cages from the 
upper layers of the water column where sea lice are 
most abundant. Closed containment systems 
however, fully separate the fish and water within the 
cage from the surrounding body of water. Pumps 
inside the cages facilitate water flow, drawing water 
from below the “lice belt” while also ensuring proper 
circulation of water within the cage. Submerged 
cages resemble conventional cages and are open in 
the sense that water flow is not obstructed by any 
other barriers than nets. These cages are submerged, 
meaning that the fish are held at certain depth, below 
the “lice belt” with a net ceiling containing an air 
dome supplying the salmon with air to fill its swim 
bladder and exhibit natural behaviour.

Requirements from the authorities provide a definition, at any given time, of the upper maximum limit for fully grown female lice. Lerøy has also established their own limit values to provide guidelines for when to implement preventive and active measures to control sea lice levels.

The average values for lice in the facilities shall be reduced by more than 50% during the period from April to June when compared with the rest of the year. This is when wild salmon migrate as smolt from the rivers to the oceans.

How we measure our impact

Sea lice counts and registration are carried out at a minimum of every seven days for all cages in each facility. This is either done manually by catching the fish in a landing net or automatically by underwater camera technology. If done manually, the fish are anaesthetised in tanks and controlled individually. A representative selection of fish is taken from each cage. Lice are counted in the following categories in terms of stages:

1) Adult female (with and without egg strings)

2) Mobile pre-adults (including adult males)

3) Attached juveniles

An average figure is calculated by totalling the number of all lice from all fish (plus lice in the tank for counting) and dividing this number by the total number of fish studied. The weighted average for the farm is calculated based on sea lice counts and the number of fish in each pen.

Infestation of wild fish by lice from Norwegian fish farms is calculated regionally by the Institute of Marine Research, by counting lice on wild salmon and using modelling. To read the Institute's report for 2023, use the following link: Lakselus – risikovurdering og kunnskapsstatus 2023 | Havforskningsinstituttet (hi.no).

Target and results

Target 2025:

• reduction of sea lice treatments to 1 150

Limits for levels of adult female lice per fish set by the authorities varies throughout the year and differ depending on region. This is described in detail in the Group´s Policy for control of sea lice.

Norwegian regulations require that the average number of adult female lice per fish per farm must be below the maximum limit of 0,5 at any time. In addition, during spring where smolts typically migrate from the rivers to the ocean, the average number of female lice per fish per farm must be below 0,2.

This period is defined as:

Week 16 up to and including week 21 in Trøndelag County and further south.

Week 21 up to and including week 26 in Nordland County and further north.

The target of reducing number of sea lice treatments 
to 1 150, relates to the objectives of the fish health 
and fish welfare policy, which is to ensure the health 
and well-being of fish as it is a main driver behind 
reduced welfare in the Group’s farming operations. The 
target is absolute and is measured as the number of 
cages treated for lice during the reporting year. The 
scope of the target includes all Lerøy’s sea-based 
farming in Norway.

Action taken due to results

Lerøy’s efforts to control salmon sea lice shall continue to follow the principles of an IPM strategy to control salmon sea lice and keep the numbers at a low level in the long term. The goal is to reduce the negative impact on the environment and the need for active interventions. Below is a description of the overall principles underlying this control strategy.

Preventive measures: Prevention is the first line of defence, aiming to control the levels of salmon sea lice by making use of passive control mechanisms. The methods utilised depend on local prerequisites and entail use of one or more of the following measures: Structural measures relating to use of locality, zone collaboration, fallow periods in between production cycles, post smolt strategy and different types of physical barriers.

Biological control: cleaner fish represent a method for treatment prevention, and the goal is to reduce the need for active measures.

Non-medicinal methods: These methods are based on different types of measures that do not include the use of medicines. Lerøy makes use of methods within the categories for fresh water, flushing and temperate water.

Medicinal methods: These methods are based on the use of medicines. In cases where medicines are utilised, these shall be 1) prescribed by authorised fish health personnel and 2) evaluated with regards to the risk for fish welfare, food safety, environment and resistance, and 3) where only medicines approved by Norwegian medicines authorities can be used.

New semiclosed technology: Lerøy has made significant investments  in coastal production technology recently. A combination of submersible and semi-closed cages is now being rolled out at selected locations in Lerøy Midt and Lerøy Sjøtroll . We believe this will have a positive impact on fish health, and reduce the lice load. This is because the cages are lowered below lice level in the sea, thus protecting the fish from lice.

Policy: Control of salmon lice