Appendix 13 – Parasite Management (Sea Lice)

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Appendix 13 – Parasite Management (Sea Lice)

by Contact on 30 October 2026

This Appendix details:

Section

13.1 Introduction

13.2 Area-Based Management (ABM) scheme (Indicators 4.5.1 and 4.5.2)

13.3 Method for the collection of sea lice data on native salmonids (Indicator 4.5.4)

13.4 Method for on-site sea lice sampling (Indicator 4.5.6)

13.5 On-site sea lice thresholds for sensitive periods (Indicator 4.5.9)

13.6 Method for calculating the Weighted Number of Medicinal Treatments (WNMT) (Indicator 4.5.12)

13.1 Introduction

Effective sea lice management is essential to protect the health of both farmed and native salmonid populations. An element of management includes setting limits to the number of on-site sea lice to ensure the health and welfare of farmed fish and minimise the risk of sea lice from farmed fish origin affecting native populations, especially during sensitive periods such as the out-migration.

Effective management also includes the cooperation of multiple sites within a specific area to manage sea lice collectively. This Area-Based Management approach helps reduce the overall sea lice burden and mitigate the risk of infestation spreading between sites. Key elements of this cooperation include the coordination of activities, such as stocking, treatment and fallowing, and information sharing.

Parasiticide treatments are used to reduce the number of sea lice on farmed fish. However, relying heavily on these chemical treatments is not a sustainable long-term solution, as they pose challenges related to environmental impact, the development of resistance, and the health and welfare of the farmed fish. Addressing these challenges requires alternatives to chemical parasiticide treatments aiming to reduce their use and ultimately eliminate reliance on them.

13.2 Area-Based Management – ABM (Indicators 4.1.1.11.1, 4.5.1 and 4.5.2)

13.2.1 Attributes of the ABM (Indicator 4.1.1.11.1 and 4.5.1)

The purpose of the ABM scheme is to improve health and biosecurity management at the site, ultimately aiming to reduce potential negative impacts on native fish populations.

A. Definition of the ‘area’

The area covered by the ABM shall reflect a logical geographic scope, such as a fjord or a group of ecologically-connected fjords.

The boundaries of the area shall be defined considering:

  1. The zone where significant cumulative impacts on native fish may occur; and

  2. Hydrodynamic characteristics of the waterbody; and

  3. Other relevant aspects of ecosystem structure and function.

If an ABM is a regulatory requirement and its definition of ‘area’ aligns with these considerations, sites may use that definition for the requirements in Criterion 4.5.

B. Participation in the ABM

At least 80% of farmed salmonid production in the area, by weight, shall participate in the ABM.

Participation shall include all sites owned by ASC Certificate Holders, including those that are not ASC-certified, and ASC applicants.

C. Documentation

The ABM shall document the following:

  • The name of the companies and sites participating in the ABM; and

  • The name and contact details of the responsible person for each site participating in the ABM; and

  • The shared ABM objectives for disease management, related to understanding and minimising the risk of on-site disease transfer to native fish species.

The objectives shall be reviewed and revised as necessary based on new information, including substantiated concerns raised by communities or local native fish interest groups as part of engagement with stakeholders required by Indicator 3.13.4.

D. Information and Data Sharing

The ABM shall ensure the sharing of information and data amongst sites to facilitate effective coordination, including at least the following:

  • Plans for stocking and fallowing; and

  • Disease and parasite monitoring results, including sea lice levels (see Indicators 4.1.1.10, 4.5.4 and 4.5.6); and

  • Therapeutic treatments; and

  • Resistance monitoring results, including information on treatments that do not produce the expected efficacy (see Indicators 4.4.8, 4.4.9 and 4.5.14); and

  • Suspected presence of an unidentifiable transmissible pathogenic agent; and

  • Confirmed presence of a WOAH-notifiable disease (see Indicator 4.1.1.11.1).

E. Coordination

The ABM shall include coordination amongst sites regarding:

  • Stocking: It shall be demonstrated that:

    • all stocked fish in the ABM are of the same year; and

    • stocking is coordinated.

  • Treatments: It shall be demonstrated that a coordinated treatment plan is implemented within the ABM. The plan shall consider the following:

    • rotation of treatments; and

    • monitoring cumulative use of antimicrobials, including antiparasitics, within the ABM, by chemical, annually, and by production cycle; and

    • assessing the potential risks to human health from the development of resistance by the cumulative use of antimicrobials listed as Highest Priority Critically Important Antimicrobials (HPCIA) or Critically Important Antimicrobials (CIA), or Highly Important Antimicrobials (HIA) by the World Health Organisation (WHO)155155https://www.who.int/publications/i/item/9789241515528. The use of antimicrobials listed as Highly Important for Human Medicine shall be considered a last resort.

  • Fallowing: It shall be demonstrated that fallowing between each production cycle is coordinated so there is a period when there are no farmed fish in the ABM.

13.2.2 Establishment, review and revision of ABM sea lice load and on-site sea lice levels (Indicator 4.5.2)

In areas with native salmonids, Indicator 4.5.2 requires the ABM to establish, review and potentially revise the maximum sea lice load. The purpose is to assess the potential cumulative infection pressure from on-site sea lice, expressed as the number of sea lice on all sites in the ABM. This maximum sea lice load provides accurate information on the potential risks to native salmonid populations.

  • The ABM shall initially establish the maximum total load based on the regulatory requirements applicable to the region or jurisdiction (i.e. the maximum on-site lice levels set by regulators during the sensitive period, multiplied by the number of farmed salmonids in the ABM).hOver time, the ABM shall demonstrate how the collected sea lice data on native salmonids required by Indicator 4.5.4 is used to review and potentially revise the maximum sea lice load for the ABM each year and/or production cycle. hrevisions to the ABM maximum sea lice load shall lead to corresponding limits on sea lice levels at individual sites during sensitive periods

    • if collected sea lice data on native salmonids demonstrates that the on-site sea lice thresholds for sensitive periods outlined in Table 1 are not protective of native salmonids, the sites shall establish a lower threshold in subsequent sensitive periods

    • conversely, data consistently demonstrating healthy native salmonid populations allows for a level higher than the established threshold. In this case, a Variance Request (VR)156156Variance Request (VR) Procedure shall be submitted to ASC to revise the threshold for the entire ABM.

  • the revision shall document how the ABM is being protective of native salmonids through the interpretation of sea lice data. Specifically, the review shall:

    • include a final recommendation and justification for maintaining or revising maximum sea lice loads in the ABM and the on-site sea lice thresholds; and

    • be documented and made available to the Conformity Assessment Body (CAB). Documentation shall include, as a minimum, the following:

      • the names of participating sites/companies, including responsible persons for each site; and

      • meeting minutes that include recommendations, justifications and actions.

13.3 Method for collecting sea lice data on native salmonids (Indicator 4.5.4)

The purpose is to clarify the correlation between sea lice occurrence in native and farmed salmonids through objective data. The collected data provides meaningful information for the ABM review of the maximum sea lice load (see Indicator 4.5.2 and Section 13.2.2).

Data collection shall conform with the following:

  • The monitoring, data collection and analysis of results demonstrate scientific rigour in the sampling size, location, species sampled, which shall be chosen based on relevance to the area (e.g. out-migrating salmon juveniles, coastal sea trout and Arctic char) and method; and

  • Monitoring is conducted yearly and is geographically relevant to the area where the site/ABM is located; and

  • Metrics include numbers of sea lice per fish, abundance and prevalence; and

  • The monitoring involves the participation of third parties, such as independent scientists.

An exception applies where:

  • Data is collected by regulators and made publicly available, in which case sites shall demonstrate the use of this data to revise the maximum sea lice load required by Indicator 4.5.2; or

  • Applicable legal requirements prohibit the handling of native salmonids, in which case sites shall provide evidence that populations are being monitored, though direct involvement in the monitoring is not required.

13.4 Method for on-site sea lice sampling (Indicator 4.5.6)

The on-site sea lice sampling shall conform with the following:

  • Frequency: weekly sampling during the sensitive period. Monthly sampling during the rest of the year.

  • An exception applies where deviation from the sampling frequency during the sensitive period is justified by a registered veterinarian or aquatic animal health professional for any of the following reasons:

  • immediately after smolting and stocking; or

  • environmental conditions that affect the welfare of the fish; or

  • fish undergoing a disease event and/or being treated, in which case the maximum deviation shall be two weeks; or

  • adherence to anaesthetic withdrawal periods associated with planned harvests.

  • The reason for any deviation shall be recorded.

  • Number of cages: at least 50% of cages sampled over a 2-week period, with the entire site sampled over at least a 6-week period.

  • Number of fish per cage: a minimum of 10 fish samples per cage.

  • Sea lice stage: at a minimum, provide data on mobiles (i.e. pre-adult and adult sea lice males) and adult female sea lice.

  • Sites shall ensure that sea lice detached from the fish while sampling are included in the final sampling count.

  • Sites shall conduct on-site sea lice sampling during the month prior to the sensitive period for the purpose of achieving sea lice levels below the thresholds for sensitive periods outlined in Section 13.5 at the time of the first sampling event within the sensitive period.

13.5 On-site sea lice thresholds for sensitive periods (Indicator 4.5.9)

Indicator 4.5.9 requires that on-site sea lice levels remain below the thresholds outlined in Table 1 during sensitive periods.

Table 1 Sea lice thresholds and sensitive period per region

Region

Sea Lice Thresholds (L. salmonis)*

Sensitive Period**

Canada (West Coast)

3 motile***

1st March to 30th June

Faroe Islands

0.5 adult female

1st May to 31st July

Iceland

0.5 mature female

Not established

Ireland

0.3 ovigerous female

1st March to 31st May

Norway

0.2 adult female

  • Nord-Trøndelag and southwards: weeks 16 to 21

  • Nordland, Troms and Finnmark: week 21 to 26

Scotland

0.5 adult female

1st February to 30th June

* In regions where a threshold is not established, 0.2 adult females apply.

**In regions where a sensitive period is not established, the length and timing should be specified according to a defined criterion (e.g. when juveniles are in proximity to cages) and using the latest knowledge.

***Motile includes adult L. salmonis females (with or without egg strings) and other motile L. salmonis (including adult males and preadults). Mobile is considered a synonym of motile.

13.6 Method for calculating the Weighted Number of Medicinal Treatments (WNMT) (Indicator 4.5.12)

The Weighted Number of Medicinal Treatments (WNMT) is the total number of medicinal parasiticide treatments applied on a site over the production cycle157157Hydrogen peroxide (H2O2) is considered a medicinal parasiticide treatment.. Indicator 4.5.12 requires sites to meet an Entry Level (EL) that expresses an initial WNMT to conform with, after which a 25% reduction needs to be achieved until the WNMT meets a defined Global Level (GL) (see Indicator 4.5.13). Table 2 shows the EL and GL per region.

Table 2 Entry Level and Global Level per region

Region*

Entry Level (EL)**

Global Level (GL)**

Canada (West Coast)

1

3***

Canada (East Coast)

9

Chile

9

Faroe Islands

6

Iceland

6

Ireland

3

Norway

5

Scotland

9

*In regions not listed, an EL of 6 and GL of 3 shall apply.

**Partial treatments (i.e. treatments applied to some cages from the total number of cages in use) should be counted as a proportion of the cages treated.

*** An exception applies where two times a ‘coupled treatment158158A “coupled treatment” is defined as a bath treatment applied in two treatment events (i.e., one treatment at t1 and a follow-up treatment at t2). Each treatment (t1 and t2) shall be included in the calculation of the WNMT.’ is given (counted as 2+2 = 4 WNMT), in which case a GL of 4 applies. Additional treatments applied will result in an exceedance of GL=4.